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Sheahan Diamond Literature Technical Reference Compilation 2020


The Sheahan Diamond Literature Reference Compilation
The Sheahan Diamond Literature Reference Compilation is compiled by Patricia Sheahan who publishes on a monthly basis a list of new scientific articles related to diamonds as well as media coverage and corporate announcementscalled the Sheahan Diamond Literature Service that is distributed as a free pdf to a list of followers. Pat has kindly agreed to allow her work to be made available as an online digital resource at Kaiser Research Online so that a broader community interested in diamonds and related geology can benefit. The references are for personal use information purposes only; when available a link is provided to an online location where the full article can be accessed or purchased directly. Reproduction of this compilation in part or in whole without permission from the Sheahan Diamond Literature Service is strictly prohibited. Return to Diamond Resource Center
Sheahan Diamond Literature Reference Compilation - Scientific Articles by Author for all years
A-An Ao+ B-Bd Be-Bk Bl-Bq Br+ C-Cg Ch-Ck Cl+ D-Dd De-Dn Do+ E F-Fn Fo+ G-Gh Gi-Gq Gr+ H-Hd He-Hn Ho+ I J K-Kg Kh-Kn Ko-Kq Kr+ L-Lh
Li+ M-Maq Mar-Mc Md-Mn Mo+ N O P-Pd Pe-Pn Po+ Q R-Rh Ri-Rn Ro+ S-Sd Se-Sh Si-Sm Sn-Ss St+ T-Th Ti+ U V W-Wg Wh+ X Y Z
Sheahan Diamond Literature Reference Compilation - Media/Corporate References by Name for all years
A B C D-Diam Diamonds Diamr+ E F G H I J K L M N O P Q R S T U V W X Y Z
Tips for Users
Posted/Published Reference CodesThe SDLRC provides 3 types of references identified in the reference code. DS for scientific article, DM for a media article, and DC for a corporate announcement. Consider DS0512-0001. The DS stands for "diamond scientific". 05 stands for 2005, the year the reference was posted. 12 represents the month the reference was posted. For all years prior to 2015 the default month is 12. -0001 is the reference's identifier and it does not mean anything. The number below the refence code, ie 2015, is the year the article was published. Note that the posted year may sometimes be later than the published year.
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Most RecentIf the reference code is highlighted yellow, the reference was made available through the most recent monthly compilation of new literature. Use this to check out new references. When new references are posted, we make it our priority to track down an online link and obtain an abstract. With regard to older references, tracking down an abstract and an online link is a work in progress.
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Monthly Sheahan Diamond Newsletters for 2020
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April 2020 August 2020 December 2020
2020 Technical Reference Compilation
Posted/
Published
AuthorTitleSourceRegionKeywords
DS202005-0717
2020
Abdel Halim, A.H., Helmy, H.H., Elhaddad, M.A., El-Mahallawi, M., Mogessie, A.Petrology of a Neoproteroxoic mantle peridotite-chromitite association from Abu Dahr area, eastern Egypt Desert, Egypt: infiltration of boninitic melt in highly depleted harzburgite.Journal of African Earth Sciences, Vol. 165, 18p. PdfAfrica, EgyptBoninite

Abstract: Peridotites of Abu Dahr represent the main litho-unit of a Neoproterozoic dismembered ophiolite sequence and are among the best-preserved and well-exposed mantle rocks in South Eastern Desert of Egypt. Here, we present new geochemical and mineral chemical data for peridotites and associated pyroxenites and for chromitites and their platinum-group minerals to constrain their petrogenesis and geotectonic setting. The Abu Dahr ophiolite mantle section consists mainly of harzburgites, cut by pyroxenite dykes and containing dunite-chromitite lenses. The harzburgites are composed of olivine, orthopyroxene, spinel and minor clinopyroxene (?1.0 vol %) and amphibole. Olivine from harzburgites is highly magnesian (Fo 91-93) and Cr-spinel shows a wide-range of Cr2O3 and Al2O3 contents. The enstatite component of orthopyroxene decreases from harzburgite (En = 90-91) to orthopyroxenite (En = 84-87). Amphiboles are represented by magnesiohornblende and tschermakite. The chromitites are massive to disseminated and composed of magnesiochromite with high Cr# (83-93) and Mg# (66-79), and low TiO2 (<0.1 wt%) content. Solid inclusions in chromite include olivine, orthopyroxene and hornblende. Laurite (RuS2) is the most common PGM detected in the investigated chromitite samples and forms micrometer-size inclusions in fresh chromite. Various Ni-sulfides are found both in fresh chromite and along serpentine veinlets. Harzburgites have a refractory composition with a very low Al2O3 (0.4-0.8 wt%) and CaO (0.2-1.6 wt%) contents and high bulk-rock Mg# (89-92). Geochemical data suggest that the Abu Dahr peridotites are highly depleted SSZ peridotites formed in a forearc mantle wedge setting by high degrees of hydrous partial melting and emplaced as a result of the collision of the intra-oceanic arc with the Beitan gneisses. The podiform chromitites and orthopyroxenites were formed due to impregnation of mantle wedge harzburgites by boninitic melt. The highly depleted nature of the harzburgite is responsible for the small reserves of chromite ore at Abu Dahr and in the South Eastern Desert in general.
DS202007-1120
2020
Abe, N., Surour, A.A., Madani, A.A., Arai, S.Metasomatized peridotite xenoliths from the Cretaceous rift related Natash volcanics and their bearing on the nature of the lithospheric mantle beneath the southern part of the eastern desert of Egypt.Lithos, in press available , 47p. PdfAfrica, Asia, Egyptperidotites

Abstract: Highly carbonated mantle xenoliths have been found in rift-related alkaline basalts at the Wadi Natash area in the southern part of the Eastern Desert of Egypt. Although all olivine and most orthopyroxene was replaced by carbonate and/or quartz, textural and mineral chemical features show that they are plagioclase-free spinel peridotites (lherzolite to harzburgite). Cr and Mg numbers (Cr#, Mg#) of Cr-spinel vary from 0.06 to 0.45 and 0.73 to 0.81, respectively. The correlation between Cr# and Mg# of the Cr-spinel in the studied xenoliths is weakly negative and its TiO2 content is slightly higher than in abyssal peridotite that was not affected by melt injection. The chemistry of ortho- and clinopyroxene suggests enstatite and chromian diopside compositions, respectively, with distinct signatures of a sub-continental mantle source. In particular, the Na2O contents (>1.0?wt%) and AlVI/AlIV ratios (1.2-2.6) of chromian diopside suggest such an origin. Two-pyroxene geothermometry indicates a temperature of about 900?°C, which is slightly lower than that of ordinary spinel peridotite xenoliths from other rift zones. It is evident that the studied peridotite xenoliths had experienced mantle processes (e.g. decompression melting, magma upwelling and metasomatism) at higher pressure than abyssal peridotites. The trace-element chemistry of clinopyroxene, e.g. high LREE/HREE ratios {(Ce/Yb)n?=?7}, high LREE contents (>3.6?ppm and up to 30.0?ppm Ce) and high Sr between >85.6?ppm and 466?ppm, indicates metasomatic alteration of the peridotite. Clinopyroxene in one sample has very low Ti/Eu and high LREE/HREE ratios. Clinopyroxene with (Ce/Yb)n higher than 3-4 and Ti/Eu ratio lower than 1500 may have experienced carbonatite or carbonate-rich melt metasomatism prior to their incorporation into the host basalt. The basalt itself is almost devoid of any carbonatization and hence the studied mantle peridotites were carbonatized before the generation of the basaltic magma but following an earlier event of K-metasomatism as indicated by the presence of phlogopite. The studied peridotites from the Wadi Natash area were altered by a carbonate-rich melt during a rifting stage. The results of the present paper indicate that the Natash basalts with their peridotite xenoliths extruded along transversal fractures of the NW-trending Nuqra-Kom Ombo-Kharit continental rift on its western shoulder in the south Eastern Desert of Egypt.
DS202003-0329
2020
Abersteiner, A., Kamenetsky, V.S., Goemann, K.A genetic study of olivine crystallization in the Mark kimberlite ( Canada) revealed by zoning and melt inclusions.Lithos, In press available 46p. pdf.Canada, Northwest Territoriesdeposit - Mark

Abstract: Elucidating the composition of primary kimberlite melts is essential to understanding the nature of their source, petrogenesis, rheology, transport and ultimately the origin of diamonds. Kimberlite rocks are typically comprised of abundant olivine (~2560 vol%), which occurs as individual grains of variable size and morphology, and includes xenocrysts and zoned phenocrysts. Zoning patterns and inclusions in olivine can be used to decipher the petrogenetic history of kimberlites, starting from their generation in the mantle through to emplacement in the crust. This study examines well-preserved, euhedral, zoned olivine crystals from the Mark kimberlite (Lac de Gras, Canada). Olivine typically consists of xenocrystic cores, which are homogeneous in composition but vary widely between grains (Fo88.193.6). These cores are in turn surrounded by (in order of crystallisation) magmatic rims and Mg-rich rinds (Fo95.398.1). In addition, we document a new type of olivine zone (‘outmost rind’) that overgrows Mg-rich rinds. Crystal and melt/fluid inclusions are abundant in olivine and preserve a record of kimberlite melt evolution. For the first time in the studies of kimberlite olivine, we report primary melt inclusions hosted in Mg-rich olivine rinds. In addition, we observe that pseudosecondary melt/fluid inclusions are restricted to interior olivine zones (cores, rims) and are considered to have formed prior to rind formation. Pseudosecondary melt/fluid inclusions are inferred to have been entrapped at depth, as evidenced by measured densities in thermometric experiments of CO2 and decrepitation haloes, indicating a minimum entrapment pressure of ~200450 MPa (or ~615 km). Both primary and pseudosecondary melt inclusions in olivine have daughter minerals dominated by CaMg and K-Na-Ba-Sr-bearing carbonates, K-Na-chlorides along with subordinate silicates (e.g., phlogopite, monticellite), Fe-Mg-Al-Ti-spinel, perovskite, phosphates and sulphates/sulphides and periclase. In addition to phases reported in primary melt inclusions, pseudosecondary melt inclusions contain more diverse and exotic daughter mineral assemblages, where they contain phases such as tetraferriphlogopite Ba- or K-sulphates, kalsilite and Na-phosphates. The daughter mineral assemblages are consistent with a silica-poor, alkali dolomitic carbonatite melt. We demonstrate that the different types of inclusions in olivine can assist in constraining the timing of multi-stage olivine growth and the composition of the crystallising melt. The large variance in olivine zoning patterns, morphologies and Ni distribution (i.e. both coupling with and decoupling from Fo) indicates that olivine in the studied Mark kimberlite samples represent an accumulation of olivine, where olivine was derived from successive stages of the ascending magma and/or from multiple, but related pulses of magma. Primary and pseudosecondary melt/fluid inclusions in olivine indicate that a variably differentiated silica-poor, halogen-bearing, alkali-dolomitic melt crystallised and transported olivine in the Mark kimberlite.
DS202008-1365
2020
Abersteiner, A., Kamenetsky, V.S., Goemann, K., Kjarsgaard, B.A., Fedortchouk, Y., Ehrig, K., Kamenetsky, M.Evolution of kimberlite magmas in the crust: a case study of groundmass and mineral hosted inclusions in the Mark kimberlite ( Lac de Gras, Canada).Lithos, in press available, 55p. PdfCanada, Northwest Territoriesdeposit - Mark

Abstract: Kimberlites are the surface manifestation of deeply-derived (>150 km) and rapidly ascended magmas. Fresh kimberlite rocks are exceptionally rare, as most of them are invariably modified by pervasive deuteric and/or post-magmatic fluids that overprint the original mineralogy. In this study, we examined fresh archetypal kimberlite from the Mark pipe (Lac de Gras, Canada), which is characterised by well-preserved olivine and groundmass minerals. The sequence of crystallisation of the parental melt and its major compositional features, including oxygen fugacity, were reconstructed using textural relationships between magmatic minerals, their zoning patterns and crystal/melt/fluid inclusions. Crystal and multiphase primary, pseudosecondary and secondary melt/fluid inclusions in olivine, Cr-diopside, spinel, perovskite, phlogopite/kinoshitalite, apatite and calcite preserve a record of different stages of kimberlite melt evolution. Melt/fluid inclusions are generally more depleted in silica and more enriched in alkalis (K, Na), alkali-earth (Ba, Sr) and halogens (Cl, F) relative to the whole-rock composition of the Mark kimberlite. These melt/fluid inclusion compositions, in combination with presence of elevated CaO (up to 1.73 wt%), in Mg-rich olivine rinds, crystallisation of groundmass kinoshitalite, carbonates (calcite, Sr-Ba-bearing) and alkali-enriched rims around apatite suggest that there was progressive enrichment in CO2, alkalis and halogens in the evolving parental melt. The Mark kimberlite groundmass is characterised by the following stages of in-situ crystallisation: (1) olivine rims around xenocrystic cores + Cr-spinel/TIMAC. (2) Mg-rich olivine rinds around olivine rims/cores + MUM-spinel (followed by pleonaste and Mg-magnetite) + monticellite (+ partial resorption of olivine, along with the formation of ferropericlase and CO2 as a result of decarbonation reactions) + perovskite + apatite. (3) Olivine outmost rinds, which are coeval with phlogopite/kinoshitalite + apatite + sulphides + carbonate (calcite, Ba-Sr-Na-bearing varieties). In addition, oxygen fugacity of the Mark kimberlite was constrained by olivine-chromite, perovskite and monticellite oxygen barometry and showed that the parental melt became progressively more oxidised in response to fractional crystallisation. (4) Deuteric (i.e. late-stage magmatic) and/or post-magmatic (i.e. external fluids) alteration of magmatic minerals (e.g., olivine, monticellite, ferropericlase) and crystallisation of mesostasis serpentine, K-bearing chlorite and brucite (i.e. replacement of ferropericlase). The absence of any alkali (Na, K) and halogen (F, Cl) rich groundmass minerals in the Mark kimberlite may be attributed to these elements becoming concentrated in the late-stage melt where they potentially formed unstable, water-soluble carbonates (such as those observed in melt inclusions). Consequently, these minerals were most likely removed from the groundmass by deuteric and/or post-magmatic alteration.
DS202007-1121
2020
Abramov, S.S., Rass, I.T., Kononkova, N.N.Fenites of the Miaskite carbonatite complex in the Vishnevye Mountains, southern Urals, Russia: origin of the metasomatic zoning and thermodynamic simulations of the processes.Petrology, Vol. 28, 3, pp. 298-323. pdfRussia, Uralscarbonatite

Abstract: Mineral zoning in fenites around miaskite intrusions of the Vishnevye Mountains complex can be interpreted as a magmatic-replacement zonal metasomatic aureole (in D.S. Korzhinskii’s understanding): the metasomatic transformations of the fenitized gneisses under the effect of deep alkaline fluid eventually resulted in the derivation of nepheline syenite eutectic melt. Based on the P-T-fO2 parameters calculated from the composition of minerals coexisting in the successive zones, isobaric-isothermal fO2-aSiO2 and µNa2O-µAl2O3 sections were constructed with the Perplex program package to model how the fenites interacted with H2O-CO2 fluid (in the Na-K-Al-Si-Ca-Ti-Fe-Mg-O-H-C system). The results indicate that the fluid-rock interaction mechanisms are different in the outer (fenite) and inner (migmatite) parts of the zonal aureole. Its outer portion was dominated by desilication of rocks, which led, first, to quartz disappearance from these rocks and then to an increase in the Al# of the coexisting minerals (biotite and clinopyroxene). In the inner part of the aureole, fenite transformations into biotite-feldspathic metasomatic rocks and nepheline migmatite were triggered by an increase in the Na and Al activities in the system alkaline H2O-CO2 fluid-rock. As a consequence, the metasomatites were progressively enriched in Al2O3 and alkalis, and these transformations led to the development of biotite in equilibrium with K-Na feldspar and calcite at the sacrifice of pyroxene. The further introduction of alkalis led to the melting of the biotite-feldspathic metasomatites and the origin of nepheline migmatites. The simulated model sequence of metasomatic zones that developed when the gneiss was fenitized and geochemical features of the successive zones (differences in the LILE and REE concentrations in the rocks and minerals of the fenitization aureole and the Sm-Nd isotope systematics of the rocks of the alkaline complex) indicate that the source of the fluid responsible for the origin of zonal fenite-miaskite complexes may have been carbonatite, a derivative of mantle magmas, whereas the miaskites were produced by metasomatic transformations of gneisses and subsequent melting under the effect of fluid derived from carbonatite magmas.
DS202010-1824
2020
Abramov, S.S., Rass, I.T., Kononkova, N.N.Fenites of the Miasite-carbonatite complex in the Vishevye Mountains, southern Urals, Russia: origin of the metasomatic zoning and thermodynamic simulations of the processes.Petrology, Vol. 28, 3, pp. 263-286.Russia, Uralscarbonatite

Abstract: Mineral zoning in fenites around miaskite intrusions of the Vishnevye Mountains complex can be interpreted as a magmatic-replacement zonal metasomatic aureole (in D.S. Korzhinskii’s understanding): the metasomatic transformations of the fenitized gneisses under the effect of deep alkaline fluid eventually resulted in the derivation of nepheline syenite eutectic melt. Based on the P-T-fO2 parameters calculated from the composition of minerals coexisting in the successive zones, isobaric-isothermal fO2-aSiO2 and µNa2O-µAl2O3 sections were constructed with the Perplex program package to model how the fenites interacted with H2O-CO2 fluid (in the Na-K-Al-Si-Ca-Ti-Fe-Mg-O-H-C system). The results indicate that the fluid-rock interaction mechanisms are different in the outer (fenite) and inner (migmatite) parts of the zonal aureole. Its outer portion was dominated by desilication of rocks, which led, first, to quartz disappearance from these rocks and then to an increase in the Al# of the coexisting minerals (biotite and clinopyroxene). In the inner part of the aureole, fenite transformations into biotite-feldspathic metasomatic rocks and nepheline migmatite were triggered by an increase in the Na and Al activities in the system alkaline H2O-CO2 fluid-rock. As a consequence, the metasomatites were progressively enriched in Al2O3 and alkalis, and these transformations led to the development of biotite in equilibrium with K-Na feldspar and calcite at the sacrifice of pyroxene. The further introduction of alkalis led to the melting of the biotite-feldspathic metasomatites and the origin of nepheline migmatites. The simulated model sequence of metasomatic zones that developed when the gneiss was fenitized and geochemical features of the successive zones (differences in the LILE and REE concentrations in the rocks and minerals of the fenitization aureole and the Sm-Nd isotope systematics of the rocks of the alkaline complex) indicate that the source of the fluid responsible for the origin of zonal fenite-miaskite complexes may have been carbonatite, a derivative of mantle magmas, whereas the miaskites were produced by metasomatic transformations of gneisses and subsequent melting under the effect of fluid derived from carbonatite magmas.
DS202005-0718
2020
Afanasiev, V.P., Pokhilenko, N.P., Egorova, E.O., Lindenblot, E.S.The most ancient diamond crystals of the Siberian platform. Lamproites Morgogor Creek .. Ebelyakh River.Doklady Earth Sciences, Vol. 489, 2, pp. 1409-1412. pdf Russia, Siberiadiamond alluvials

Abstract: Based on a study of diamond grains from placers of the northeastern Siberian Platform, it is shown that certain types of diamonds (rounded dodecahedroids, diamonds of the II and V?VII varieties, according to the classification by Yu.L. Orlov) could have originated from Precambrian sources. “Ancient” diamonds also differ in terms of their sedimentological history: those of varieties V?VII, despite the maximum abrasion resistance, have the maximum degree of rounding, reflecting their more long-term sedimentological history, and, therefore, their ore bodies were likely the most ancient.
DS202006-0908
2020
Afanasiev, V.P., Pokhilenko, N.P., Grinenko, V.S., Kostin, A.V., Malkovets, V.G., Oleinikov, O.B.Kimberlitic magmatism in the south western flank of the Vilui basin. ( pyrope from Kenkeme River catchment) Jurassic-Cretaceous barren kimberlites.Doklady Earth Science, Vol. 490, 2, pp. 51-54.Russiageochronology

Abstract: We have analyzed 141 grains of pyrope from Neogene sediments in a quarry of construction materials, in the Kenkeme River catchment, along its left-side tributary (Chakiya River), about 60 km northwest of Yakutsk city. The mineral chemistry patterns of pyropes are typical of Jurassic-Cretaceous barren kimberlites, like the pipes of Obnazhennaya or Muza, but are uncommon to diamondiferous Middle Paleozoic kimberlites. The results allow identifying the magmatic event and placing time constraints on kimberlite magmatism in the southeastern flank of the Vilui basin, which was part of the Late Jurassic-Early Cretaceous tectonic-magmatic event in northeastern Asia.
DS202005-0719
2020
Agashev, A.M., Chervyakovskaya, M.V., Serov, I.V., Tolstov, A.V., Agasheva, E.V., Votyakov, S.L.Source rejuvenation vs. re-heating: constraints on Siberian kimberlite origin from U-Pb and Lu-Hf isotope compositions and geochemistry of mantle zircons. ( Silurian, Devonian, Triassic, Jurassic)Lithos, Vol. 364-365, 10p. PdfRussia, Siberiadeposit - Druzhba, Choumurdakh

Abstract: We have studied a suite of mantle zircons from several differently aged pipes of the Siberian kimberlite province via UPb and LuHf isotope analyses and trace element compositions. The UPb ages we obtained confirmed four main episodes (Silurian, Devonian, Triassic and Jurassic) of kimberlite activity on the Siberian craton. The Druzhba pipe had two populations of zircons dating from the Silurian and Devonian, respectively. The geochemical features of our suite of mantle zircons show low concentrations of U, Th and heavy rare earth elements (REEs), positive Ce anomalies, and weak or absent Eu anomalies, which is in accord with the mantle-derived nature of the zircon. Despite having broadly similar geochemistry, zircons from differently aged kimberlites had some clear differences arising from variations in the composition of the protokimberlite metasomatic melt and from peculiarities of fractional crystallization. The Th/U ratios were highest in the Silurian zircons and sharply decreased toward the Devonian. The Triassic zircons had elevated and highly variable Ce/Nb ratios with low and nearly constant Th/U ratios. Zircons from Siberian kimberlites with different UPb ages showed systematic variations in their initial Hf isotope compositions. The oldest Silurian kimberlite field, Chomurdakh, had two zircon populations: Silurian zircons, with ?Hft values in the range of +2.8 to +5.9 units, and Devonian zircons, with ?Hft values in the range of +1.6 to +2.0 units. Zircons from the Devonian field kimberlites were in the range of +5.6 to +9.6 ?Hft units. The Triassic kimberlitic zircons had the most juvenile Hf isotope composition, at +9.3 to +11.2 ?Hft units, while the Jurassic zircons had +6.9 ?Hft units. The combination of the UPb and LuHf isotope data suggests a periodic rejuvenation of the lithospheric mantle roots by low-volume melts from the asthenospheric mantle, resulting shortly after in kimberlite emplacements. Some Devonian and Jurassic kimberlites may have been melted by re-heating the Silurian and Triassic age sources, respectively, about 60 Myr after they were formed.
DS202009-1605
2020
Amsellem, E., Moynier, F., Bertrand, H., Bouyon, A., Mata, J., Tappe, S., Day, J.M.D.Calcium isotopic evidence for the mantle sources of carbonatites. ( Oldoinyo Lengai)Science Advances, Vol. 6, eaba3269 June 3, 7p. PdfGlobal, Africa, Tanzaniacarbonatites

Abstract: The origin of carbonatites-igneous rocks with more than 50% of carbonate minerals-and whether they originate from a primary mantle source or from recycling of surface materials are still debated. Calcium isotopes have the potential to resolve the origin of carbonatites, since marine carbonates are enriched in the lighter isotopes of Ca compared to the mantle. Here, we report the Ca isotopic compositions for 74 carbonatites and associated silicate rocks from continental and oceanic settings, spanning from 3 billion years ago to the present day, together with O and C isotopic ratios for 37 samples. Calcium-, Mg-, and Fe-rich carbonatites have isotopically lighter Ca than mantle-derived rocks such as basalts and fall within the range of isotopically light Ca from ancient marine carbonates. This signature reflects the composition of the source, which is isotopically light and is consistent with recycling of surface carbonate materials into the mantle.
DS202007-1122
2020
Amsellem, E., Moynier, F., Betrand, H., Bouyon, A., Mata, J., Tappe, S., Day, J.M.D.Calcium isotopic evidence for the mantle source of carbonatites.Science Adavances, Vol. 6, 63 eaba3269 6p. PdfMantlecarbonatite

Abstract: The origin of carbonatites—igneous rocks with more than 50% of carbonate minerals—and whether they originate from a primary mantle source or from recycling of surface materials are still debated. Calcium isotopes have the potential to resolve the origin of carbonatites, since marine carbonates are enriched in the lighter isotopes of Ca compared to the mantle. Here, we report the Ca isotopic compositions for 74 carbonatites and associated silicate rocks from continental and oceanic settings, spanning from 3 billion years ago to the present day, together with O and C isotopic ratios for 37 samples. Calcium-, Mg-, and Fe-rich carbonatites have isotopically lighter Ca than mantle-derived rocks such as basalts and fall within the range of isotopically light Ca from ancient marine carbonates. This signature reflects the composition of the source, which is isotopically light and is consistent with recycling of surface carbonate materials into the mantle.
DS202011-2026
2020
Anenburg, M.Rare earth mineral diversity controlled by REE pattern shapes.Mineralogical Magazine, doi.10.1180/mgm.2020.70 11p. PdfMantleREE

Abstract: The line connecting rare earth elements (REE) in chondrite-normalised plots can be represented by a smooth polynomial function using ? shape coefficients as described by O'Neill (2016). In this study, computationally generated ? combinations are used to construct artificial chondrite-normalised REE patterns that encompass most REE patterns likely to occur in natural materials. The dominant REE per pattern is identified, which would lead to its inclusion in a hypothetical mineral suffix, had this mineral contained essential REE. Furthermore, negative Ce and Y anomalies, common in natural minerals, are considered in the modelled REE patterns to investigate the effect of their exclusion on the relative abundance of the remainder REE. The dominant REE in a mineral results from distinct pattern shapes requiring specific fractionation processes, thus providing information on its genesis. Minerals dominated by heavy lanthanides are rare or non-existent, even though the present analysis shows that REE patterns dominated by Gd, Dy, Er and Yb are geologically plausible. This discrepancy is caused by the inclusion of Y, which dominates heavy REE budgets, in mineral name suffixes. The focus on Y obscures heavy lanthanide mineral diversity and can lead to various fractionation processes to be overlooked. Samarium dominant minerals are known, even though deemed unlikely by the computational model, suggesting additional fractionation processes that are not well described by ? shape coefficients. Positive Eu anomalies only need to be moderate in minerals depleted in the light REE for Eu to be the dominant REE, thus identifying candidate rocks in which the first Eu dominant mineral might be found. Here, I present an online tool, called ALambdaR that allows interactive control of ? shape coefficients and visualisation of resulting REE patterns.
DS202010-1825
2020
Anenburg, M., Mavrogenes, J.A., Bennett, V.C.The fluorapatite P-REE-Th vein deposit at Nolans Bore: genesis by carbonatite metasomatism.Journal of Petrology, Vol. 61, 1, egaa003 42p. PdfAustralia, Northern Territorydeposit - Nolans Bore

Abstract: Nolans Bore is a rare earth element (REE) ore deposit in the Reynolds Range, Aileron Province, Northern Territory, Australia. It consists primarily of fluorapatite and alteration products thereof, surrounded by a diopside-dominated selvage. Previously considered to form via hydrothermal fluids, we now suggest that the deposit formed by a metasomatic reaction between a mantle-derived carbonatite and granulite-facies felsic host rocks, after peak metamorphism. REE patterns of fluorapatite are strongly light REE (LREE) enriched, convex with maxima at Ce to Nd, and contain a weak negative Eu anomaly. Textural and geochemical properties of the fluorapatite are consistent with its formation from a carbonatite liquid. Sinusoidal REE patterns in diopside along with strong Yb-Lu enrichment relative to coexisting titanite are suggestive of derivation from a Ca-rich carbonatite. Likewise, hyalophane present in the selvages forms by reaction of a BaCO3 component in the carbonatite with K-feldspar in the silicate host rocks. The overall morphology of Nolans Bore is consistent with carbonatite-silicate reaction experiments, with the carbonatite itself migrating elsewhere owing to the open-system nature of Nolans Bore. Ekanite veins in massive fluorapatite zones and allanite-epidote crusts on fluorapatite in contact with the diopside selvages formed by hydrothermal fluids exsolved from the carbonatite. Minor interstitial calcite was not igneous but was the last mineral to crystallize from the carbonatite-exsolved fluid. Y/Ho ratios qualitatively trace the transition from mantle-dominated igneous minerals to later low-temperature hydrothermal minerals. Rb-Sr and Sm-Nd analyses of unaltered minerals (fluorapatite, allanite, calcite) show that the carbonatite had homogeneous initial 87Sr/86Sr???0•7054 and ?Nd???-4 at 1525?Ma, the best age estimate of the mineralization. Fluorapatite-allanite Sm-Nd dating results in an age of 1446?±?140?Ma, consistent with forming soon after the end of the Chewings Orogeny. Neodymium depleted mantle model ages are older than 2?Ga, indicating the presence of recycled crustal material within the source. We suggest that the carbonatite was sourced from a mantle enriched by subduction of LREE-rich oceanic crustal rocks, marine sediments, and phosphorites, potentially from the south, or the Mount Isa area to the east. Nolans Bore represents the root zone of a now-eroded carbonatite. Other Nolans-type deposits (Hoidas Lake, Canada and Kasipatnam, India) are similarly hosted within siliceous granulite-facies rocks in regions with a long tectonic history, suggesting common processes that led to the formation of all three deposits. The REE-rich compositions of the mid-crustal Nolans Bore fluorapatite are the cumulates hypothesized to cause REE depletion in some unmineralized carbonatites. The rocks at Nolans Bore demonstrate that carbonatites, previously thought to be mostly unreactive, can undergo modification and modify the composition of the silicate rocks which they encounter, forming an ‘antiskarn’. At igneous temperatures, the resulting mineral assemblage (other than fluorapatite) consists of diopside and titanite, both of which are common in granulite-facies rocks. Therefore, carbonatite metasomatism can remain unnoticed if the resulting assemblage does not contain distinctively carbonatitic minerals.
DS202011-2027
2020
Anenburg, M., Mavrogenes, J.A., Frigo, C., Wall, F.Rare earth element mobility in and around carbonatites controlled by sodium, potassium, and silica.Science Advances, Vol. 6, 11p. 10.1126/sciadv.abb6570 pdfGlobalcarbonatites, REE

Abstract: Carbonatites and associated rocks are the main source of rare earth elements (REEs), metals essential to modern technologies. REE mineralization occurs in hydrothermal assemblages within or near carbonatites, suggesting aqueous transport of REE. We conducted experiments from 1200°C and 1.5 GPa to 200°C and 0.2 GPa using light (La) and heavy (Dy) REE, crystallizing fluorapatite intergrown with calcite through dolomite to ankerite. All experiments contained solutions with anions previously thought to mobilize REE (chloride, fluoride, and carbonate), but REEs were extensively soluble only when alkalis were present. Dysprosium was more soluble than lanthanum when alkali complexed. Addition of silica either traps REE in early crystallizing apatite or negates solubility increases by immobilizing alkalis in silicates. Anionic species such as halogens and carbonates are not sufficient for REE mobility. Additional complexing with alkalis is required for substantial REE transport in and around carbonatites as a precursor for economic grade-mineralization.
DS202009-1606
2020
Anzolini, C., Marquardt, K., Stagno, V., Nestola, F.Evidence for complex iron oxides in the deep mantle from FeNi(Cu) inclusions in superdeep diamondsProceedings of the National Academy of Sciences, pnas.org/cgi/doi.10.1073 /pnas.2004269117 7p. PdfMantlediamond inclusions

Abstract: The recent discovery in high-pressure experiments of compounds stable to 24-26 GPa with Fe4O5, Fe5O6, Fe7O9, and Fe9O11 stoichiometry has raised questions about their existence within the Earth’s mantle. Incorporating both ferric and ferrous iron in their structures, these oxides if present within the Earth could also provide insight into diamond-forming processes at depth in the planet. Here we report the discovery of metallic particles, dominantly of FeNi (Fe0.71Ni0.24Cu0.05), in close spatial relation with nearly pure magnetite grains from a so-called superdeep diamond from the Earth’s mantle. The microstructural relation of magnetite within a ferropericlase (Mg0.60Fe0.40)O matrix suggests exsolution of the former. Taking into account the bulk chemistry reconstructed from the FeNi(Cu) alloy, we propose that it formed by decomposition of a complex metal M oxide (M4O5) with a stoichiometry of (Fe3+2.15Fe2+1.59Ni2+0.17Cu+0.04)? = 3.95O5. We further suggest a possible link between this phase and variably oxidized ferropericlase that is commonly trapped in superdeep diamond. The observation of FeNi(Cu) metal in relation to magnetite exsolved from ferropericlase is interpreted as arising from a multistage process that starts from diamond encapsulation of ferropericlase followed by decompression and cooling under oxidized conditions, leading to the formation of complex oxides such as Fe4O5 that subsequently decompose at shallower P-T conditions.
DS202007-1123
2020
Anzolini, C., Siva-Jothy, W., Locock, A.J., Nestola, F., Balic-Zunic, T., Alvaro, M., Stachel, T., Pearson, D.G.Heamanite-(Ce) (K0.5Ce0.5)Ti03 Mineralogical Magazine reports CNMNC Newsletter , No. 55, Vol. 84, https://doi.org/ 10.1180/mgm. 2020.39Canada, Northwest Territoriesdeposit - Gahcho Kue
DS202011-2028
2020
Apen, F.E., Rudnick, R.L., Cottle, J.M., Kylander-Clark, A.R.C., Blondes, M.S., Piccoli, P.M., Seward, G.Four dimensional thermal evolution of the East African Orogen: accessory phase petrochronology of crustal profiles through the Tanzanian Craton and Mozambique belt, northeastern Tanzania.Contributions to Mineralogy and Petrology, Vol. 175, 97, 30p. PdfAfrica, Tanzaniacraton

Abstract: U-Pb petrochronology of deep crustal xenoliths and outcrops across northeastern Tanzania track the thermal evolution of the Mozambique Belt and Tanzanian Craton following the Neoproterozoic East African Orogeny (EAO) and subsequent Neogene rifting. At the craton margin, the upper-middle crust record thermal quiescence since the Archean (2.8-2.5 Ga zircon, rutile, and apatite in granite and amphibolite xenoliths). The lower crust of the craton documents thermal pulses associated with Neoarchean ultra-high temperature metamorphism (ca. 2.64 Ga,?>?900 °C zircon), the EAO (600-500 Ma rutile), and fluid influx during rifting (?650 °C (above Pb closure of rutile and apatite) at the time of eruption. Zoned titanite records growth during cooling of the lower crust at 550 Ma, followed by fluid influx during slow cooling and exhumation (0.1-1 °C/Myr after 450 Ma). Permissible lower-crustal temperatures for the craton and orogen suggest variable mantle heat flow through the crust and reflect differences in mantle lithosphere thickness rather than advective heating from rifting.
DS202010-1826
2020
Armistead, S.E., Collins, A.S., Redaa, A., Jepson, G., Gillespie, J., Gilbert, S., Blades, M.L., Foden, J.D., RazakMnN, T.Structural evolution and medium temperature thermochronology of central Madagascar: implications for Gondwana amalagamation.Journal of the Geological Society, Vol. 177, pp. 784-798.Africa, Madagascargeothermometry

Abstract: Madagascar occupied an important place in the amalgamation of Gondwana and preserves a record of several Neoproterozoic events that are linked to orogenesis of the East African Orogen. In this study, we integrate remote sensing, field data and thermochronology to unravel complex deformation in the Ikalamavony and Itremo domains of central Madagascar. The deformation sequence comprises a gneissic foliation (S1), followed by south- to SW-directed, tight to isoclinal, recumbent folding (D2). These are overprinted by north-trending upright folds that formed during an approximately east-west shortening event (D3). Together these produced type 1 and type 2 fold interference patterns throughout the Itremo and Ikalamavony domains. We show that the Itremo and Ikalamavony domains were deformed together in the same orogenic system, which we interpret as the c. 630 Ma collision of Azania with Africa along the Vohibory Suture in southwestern Madagascar. In eastern Madagascar, deformation is syn- to post-550 Ma, and probably formed in response to final closure of the Mozambique Ocean along the Betsimisaraka Suture that amalgamated Madagascar with the Dharwar Craton of India. Apatite U-Pb and novel laser ablation triple quadrupole inductively coupled plasma mass spectrometry (LA-QQQ-ICP-MS) muscovite and biotite Rb-Sr thermochronology indicates that much of central Madagascar cooled through c. 500°C at c. 500 Ma.
DS202009-1607
2020
Arnould, M., Coltice, N., Flament, N., Mallard, C.Plate tectonics and mantle controls on plume dynamics.Earth and Planetary Science Letters, Vol. 547, 15p. PdfMantlegeodynamics

Abstract: Mantle plumes provide valuable information about whole-mantle convection: they originate at the core-mantle boundary, cross Earth's mantle and interact with the lithosphere. For instance, it has been proposed that the mobility/stability of plumes depends on plume intrinsic properties, on how slabs interact with the basal boundary layer, on mantle flow, or on their proximity to mid-ocean ridges. Here, we use 3D-spherical models of mantle convection generating self-consistent plate-like behaviour to investigate the mechanisms linking tectonics and mantle convection to plume dynamics. Our models produce fully-dynamic mantle plumes that rise vertically with deflection and present excess temperatures, rising speeds, buoyancy and heat fluxes comparable to observations. In the absence of plate tectonics, plumes are stable and their lifetime exceeds hundreds of million years. With plate tectonics, plumes are more mobile, and we identify four physical mechanisms controlling their stability. 1/ Fixed plumes are located at saddle points of basal mantle flow. 2/ Plumes moving at speeds between 0.5-1 cm yr?1 are slowly entrained by passive mantle flow. 3/ Fast plume motions between 2-5 cm yr?1 lasting several tens of million years are caused by slab push. 4/ Plumes occasionally drift at speeds >5 cm yr?1 over <10 Myr through plume merging. We do not observe systematic anchoring of plumes to mid-oceanic ridges. Independent of the presence of a dense basal layer, plate-like regimes decrease the lifetime of plumes compared to stagnant-lid models. Plume age, temperature excess or buoyancy flux are not diagnostic of plume lateral speed. The fraction of plumes moving by less than 0.5 cm yr?1 is >25%, which suggests that fixed hotspot reference frames can be defined from carefully selected hotspot tracks.
DS202008-1366
2020
Artyushkov, E.V., Kolka, V.V., Chekhovich, P.A.The occurrence of lower viscosity layer in the crust of old cratons as a cause of the strongly differentiated character of postglacial uplift.Doklady Earth Sciences, Vol. 492, pp. 351-355.Europe, Fennoscandia, Kola Peninsula, Karelia, Canadacraton

Abstract: Rapid glacio-isostatic rebound in Fennoscandia and Canada that is nonuniform in time and space indicates that there is a layer with strongly decreased viscosity at shallow crustal depths. The upper boundary of the layer is near the depth of 15 km, which corresponds to the maximum depth of earthquake hypocenters in the Precambrian cratons of the Kola Peninsula and Karelia. The position of the lower boundary is less distinct; however, most likely it is located near the base of the crust. The formation of such a layer in the Pliocene-Quaternary occurred due to infiltration of a large volume of mantle fluids into the crust. In many regions, this has led to retrograde metamorphism with rock expansion and a strong decrease in rocks viscosity.
DS202009-1608
2019
Arzamastev, A., Stepanova, A.V., Samsonov, A.V., Erofeev, K.G.Mafic magmatism of northeastern Fennoscandia ( 2.06-1.86 Ga) geochemistry of volcanic rocks and correlation with dike complexes.Stratigraphy and Geological Correlation, Vol. 28, 1, pp. 1-34.Europe, Fennoscandiamagmatism

Abstract: The comprehensive geochemical and isotopic-geochronological study of Early Proterozoic volcanic rocks in structure of the Polmak-Pechenga-Imandra-Varzuga belt and dikes and sills of the Murmansk and Kola-Norwegian terranes is conducted. Abundant swarms of mafic dikes (2.06-1.86 Ga) are established in the northwestern frame of the belt, including swarms of metadolerites (2060 ± 6 Ma), ferropicrites and gabbronorites (1983 ± 5 Ma), and poikilophitic dolerites (1860 ± 4 Ma). The comparison of volcanic rocks of the Pechenga and Imandra-Varzuga structures shows asynchronous change in volcanism style, with a significant time lapse. The geochemical features of volcanic rocks of the Tominga Formation are typical of those of continental magmatism and can hardly be correlated with those of the Pilguyarvi Formation. According to isotopic-geochronological data, depleted mantle melts in the Pechenga and Imandra-Varzuga zones intruded at 2010-1970 and 1970-1980 Ma, respectively. The analysis of the conditions of formation of volcanic series shows that Neoarchean lithospheric mantle, which produced melts with low Zr/Nb ratios, was a source for primary melts of the Kuetsjarvi Formation of the Pechenga structure and their homologs of the Imandra-Varzuga structure. In contrast, the volcanic rocks of the Kolasjoki Formation, which were weakly contaminated with crustal material, and the related Ilmozero Formation, as well as the metadolerite dikes of the Kirkenes region, were sourced mostly from asthenosphere with separation of melt above the garnet stability depth. The formation of the volcanic rocks of the Pilguyarvi Formation is related, judging from the geochemical data, to two asthenospheric sources different in depth, which produced tholeiitic and ferropicritic melts.
DS202010-1827
2020
Ashchepkov, I., Medvedev, N., Vladykin, N., Ivanov, A., Downes, H.Thermobarometry and geochemistry of mantle xenoliths from Zapolyarnaya pipe, Upper Muna field, Yakutia: implications for mantle layering, interaction with plume melts and diamond grade.Minerals, Vol. 10, 9, 740 10.3390/ min10090755 29p. PdfRussia, Yakutiadeposit - Zapplyarnaya

Abstract: Minerals from mantle xenoliths in the Zapolyarnaya pipe in the Upper Muna field, Russia and from mineral separates from other large diamondiferous kimberlite pipes in this field (Deimos, Novinka and Komsomolskaya-Magnitnaya) were studied with EPMA and LA-ICP-MS. All pipes contain very high proportions of sub-calcic garnets. Zapolyarnaya contains mainly dunitic xenoliths with veinlets of garnets, phlogopites and Fe-rich pyroxenes similar in composition to those from sheared peridotites. PT estimates for the clinopyroxenes trace the convective inflection of the geotherm (40-45 mW•m?2) to 8 GPa, inflected at 6 GPa and overlapping with PT estimates for ilmenites derived from protokimberlites. The Upper Muna mantle lithosphere includes dunite channels from 8 to 2 GPa, which were favorable for melt movement. The primary layering deduced from the fluctuations of CaO in garnets was smoothed by the refertilization events, which formed additional pyroxenes. Clinopyroxenes from the Novinka and Komsomolskaya-Magnitnaya pipes show a more linear geotherm and three branches in the P-Fe# plot from the lithosphere base to the Moho, suggesting several episodes of pervasive melt percolation. Clinopyroxenes from Zapolyarnaya are divided into four groups according to thermobarometry and trace element patterns, which show a stepwise increase of REE and incompatible elements. Lower pressure groups including dunitic garnets have elevated REE with peaks in Rb, Th, Nb, Sr, Zr, and U, suggesting mixing of the parental protokimberlitic melts with partially melted metasomatic veins of ancient subduction origin. At least two stages of melt percolation formed the inclined PT paths: (1) an ancient garnet semi-advective geotherm (35-45 mW•m?2) formed by volatile-rich melts during the major late Archean event of lithosphere growth; and (2) a hotter megacrystic PT path (Cpx-Ilm) formed by feeding systems for kimberlite eruptions (40-45 mW•m?2). Ilmenite PT estimates trace three separate PT trajectories, suggesting a multistage process associated with metasomatism and formation of the Cpx-Phl veinlets in dunites. Heating associated with intrusions of protokimberlite caused reactivation of the mantle metasomatites rich in H2O and alkali metals and possibly favored the growth of large megacrystalline diamonds.
DS202010-1828
2011
Ashchepkov, I.V.Program of the mantle thermometers and barometers: usage for reconstructions and calibration of PT methods.Vestnik Otdelenia nauk o Zemle RAN *** ENG, Vol. 3, doi:10.2205/2011NZ000138, 5p. Pdf * note dateMantlegeobarometry, peridotites

Abstract: Original monomineral thermobarometers for mantle peridotites for clinopyroxene, garnet, chromite and ilmenites for the mantle peridotites were statistically calibrated on the PT estimates for mantle peridotites [Ashchepkov et al., 2010] were tested using the mineral phases obtained in high pressure experiments with the natural peridotites (380 runs) [Brey et al.,1990; 2008 etc] and eclogites (240 runs)[Dasgupta et al., 2006 etc]. In the original program of that written on FORTRAN are assembled the most reliable methods of mineral thermometers (45) and barometers (36) and oxybarometers (5), including original monomineral and methods [Ashchepkov, 2003 Ashchepkov et al., 2008; 2009; 2010; 2011] for the mantle peridotites bases on the compositions of on clinopyroxene, garnet, chromite and ilmenite. Program reads the text files, which converted from Excel. Original data include standard silicate compositions for 12 components in standard order. The text file includes 15 columns of 8 symbols. The first is file name which is the same for all the minerals in the association. The second is indicator symbol for phases. E- enstatite, D - diopside, O-olivine, S-spinel, G- garnet, I -ilmenite, A- amphibole, F - phlogopite, P-plagioclase, L- liquid, R- bulk rock. Then follow oxides: SiO2, TiO2, Al2O3, Cr2O3, FeO, MnO, MgO, CaO, Na2O, K2O, NiO, V2O3 written with 2-3 decimals. The last column may contain description of the mineral or association up to 64 symbols. Monomineral methods use calculated values for Fe#Ol or Fe#Cpx. The input from console includes file name (8 symbols) (A8), then amount of PT pairs of numbers thermometers and barometers (2I2) and one for FO2 method. Program allows input of the iteration numbers (to 25 by default). It allow to choose whether to use the calculated Fe3+ for the minerals and also. It is possible also to put fixed values of T and P (default 1000o C and 40 kbar ).
DS202011-2029
2001
Ashchepkov, I.V., Afanasiev, V.P., Pokhilenko, N.P., Sobolev, N.V., Vladykin, N.V., Saprykin, A.I., Khmelnikova, O.S., Anoshin, G.N.Small note on the composition of Brazilian mantle. *** NOTE DATERevista Brasileira de Geociencas*** ENG, Vol. 31, 4, pp. 653-660. pdfSouth America, Brazilkimberlites

Abstract: Garne ts from couc eru ratc from the vargcm l kimberl ite pipe show a long compos itional range and reveallong lincar tre nds within the lherzolite field in a Cr~Ol - CaO% dia gram (Sobolcv et til. 1974) (lip (0 11% MgO). fon ned by grains of different dimensions with fcw deviations to harzburg itcs . Larger grains (fraction +3) arc higher in CaO with less Cr~01 (to 5.5%). TIle Cr20 1 freq uen cy reduc es in hyperbo lic function for each fraction . IImenites reve;1142-56% Ti0 2l..'Olllpositionai range with linear FeO - MgO correhuions but 3(4) separate groups for A I ~01 suggest different proport ion of co-prccipimted gimlet , probably due to polybn ric Irncnonanon. lncreasing Cr~O l nnd r"t..-Q% conte nt (fractionation uegn:e ) with red ucing TiO~ is in accord with Ar c mod el.. Ganict xenolith fnnnldnin II pipe with large Ga r- Cpxgrains and fine Mica-Curb bearing mat rix refer to 60 kbcr and 35 mv/m2 gcothcrm . 11displays enr iched trace c lement pat ter ns but not completely equilibrated compositions for Ga r anti Cpx. sugges ting low degree me lting of rela tively fertile mantle. St udied uuuc rinlmay s uggcsrmcrasomu tized, relat ively fertile and irre gularly heated mantle bene ath Sombcrn Bra zil as found by (Carvalho & Lccnnrdos 1997).
DS202010-1829
2013
Ashchepkov, I.V., Alymova, N.V., Loginova, A.M., Vladykin, N.V., Kuligin, S.S., Mityukhin, S.I., Stegnitsky, Y.B., Prokopiev, S.A., Salikhov, R.F., Palessky, V.S., Khmelnikova, O.S.Picroilmenites in Yakutian kimberlites: variations and genetic models. Solid Earth Discussions, Vol. 5, pp. 1-75. pdf * note dateRussia, Yakutiapicroilmenites

Abstract: Major and trace element variations in picroilmenites from Late Devonian kimberlite pipes in Siberia reveal similarities within the region in general, but show individual features for ilmenites from different fields and pipes. Empirical ilmenite thermobarometry (Ashchepkov et al., 2010), as well as common methods of mantle thermobarometry and trace element geochemical modeling, shows long compositional trends for the ilmenites. These are a result of complex processes of polybaric fractionation of protokimberlite melts, accompanied by the interaction with mantle wall rocks and dissolution of previous wall rock and metasomatic associations. Evolution of the parental magmas for the picroilmenites was determined for the three distinct phases of kimberlite activity from Yubileynaya and nearby Aprelskaya pipes, showing heating and an increase of Fe# (Fe# = Fe / (Fe + Mg) a.u.) of mantle peridotite minerals from stage to stage and splitting of the magmatic system in the final stages. High-pressure (5.5-7.0 GPa) Cr-bearing Mg-rich ilmenites (group 1) reflect the conditions of high-temperature metasomatic rocks at the base of the mantle lithosphere. Trace element patterns are enriched to 0.1-10/relative to primitive mantle (PM) and have flattened, spoon-like or S- or W-shaped rare earth element (REE) patterns with Pb > 1. These result from melting and crystallization in melt-feeding channels in the base of the lithosphere, where high-temperature dunites, harzburgites and pyroxenites were formed. Cr-poor ilmenite megacrysts (group 2) trace the high-temperature path of protokimberlites developed as result of fractional crystallization and wall rock assimilation during the creation of the feeder systems prior to the main kimberlite eruption. Inflections in ilmenite compositional trends probably reflect the mantle layering and pulsing melt intrusion during melt migration within the channels. Group 2 ilmenites have inclined REE enriched patterns (10-100)/PM with La / Ybn ~ 10-25, similar to those derived from kimberlites, with high-field-strength elements (HFSE) peaks (typical megacrysts). A series of similar patterns results from polybaric Assimilation + fractional crystallization (AFC) crystallization of protokimberlite melts which also precipitated sulfides (Pb < 1) and mixed with partial melts from garnet peridotites. Relatively low-Ti ilmenites with high-Cr content (group 3) probably crystallized in the metasomatic front under the rising protokimberlite source and represent the product of crystallization of segregated partial melts from metasomatic rocks. Cr-rich ilmenites are typical of veins and veinlets in peridotites crystallized from highly contaminated magma intruded into wall rocks in different levels within the mantle columns. Ilmenites which have the highest trace element contents (1000/PM) have REE patterns similar to those of perovskites. Low Cr contents suggest relatively closed system fractionation which occurred from the base of the lithosphere up to the garnet-spinel transition, according to monomineral thermobarometry for Mir and Dachnaya pipes. Restricted trends were detected for ilmenites from Udachnaya and most other pipes from the Daldyn-Alakit fields and other regions (Nakyn, Upper Muna and Prianabarie), where ilmenite trends extend from the base of the lithosphere mainly up to 4.0 GPa. Interaction of the megacryst forming melts with the mantle lithosphere caused heating and HFSE metasomatism prior to kimberlite eruption.
DS202007-1124
2020
Ashchepkov, I.V., Vladykin, N.V., Kalashnyk, H.A., Medvedev, N.S., Saprykin, A.I., Downes, H., Khmelnikova, O.S.Incompatible element enriched mantle lithosphere beneath kimberlitic pipes in Priazovie Ukrainian shield: volatile enriched focused melt flow and connection to mature crust?International Geology Review, in press available 24p. PdfEurope, Ukrainedeposit - Priazovie

Abstract: Major, minor and trace element compositions of mantle xenocrysts from Devonian kimberlite pipes in the Priazovie give an insight into the mantle structure beneath the SE Ukranian Shield and its evolution. Garnets yield low temperature conditions as determined by monomineral thermobarometry. The mantle lithosphere is sharply divided at 4.2 GPa, marked by a high temperature Cpx-Ilm-Phl trend, eclogites and changes in pyrope geochemistry. Seven layers are detected: Ist layer at 2.5-1 GPa is enriched mantle (Fe#Ol ~ 0.11 ? 0.14) with Gar- pyroxenites and Sp peridotites; IInd at 2.5-3.2 GPa - Gar-Sp (Fe#Ol 0.08 ? 0.10) peridotite. IIId at 4.3-3.2 GPa is formed of Archaean- Proterozoic peridotites with Fe#Ol ~0.07 ? 0.095. IVth at 3.2-5 GPa- contains pyroxenitic Gar with higher Ca, eclogites, Chr and Cpx (Fe#Ol ~0.10 ? 0.125); Vth at 5.8 ? 5 GPa is marked by sub-Ca garnets, Cr-rich chromites and Mg-Cr ilmenites; VIth layer at 5.8-6.8 GPa contains Fe-enriched pyropes, almandines and Cr-Mg ilmenites near the lithosphere base; VIIth layer > 6.8 GPa consists of ‘hot’ Fe-rich garnets. Garnets show increasing enrichment in LREE, LILE, Hf, Zr with decreasing pressure. Primitive garnets have round REE patterns; depleted ones have S-type patterns inflected at Nd. Garnets from 6.5 to 3 GPa show increasing La/Ybn, Zr-Hf, LILE. Peridotitic clinopyroxenes have inclined linear trace element patterns rounded from La to Pr with high LILE and HFSE levels. The Fe-rich group (reacted with eclogites) shows bell-shaped irregular patterns with LILE close to the LREE levels. A possible reason for LILE (HFSE and) enrichment of the upper part of the mantle is subduction metasomatsm in Archaean times (with participation of mature continental sediments) activated by plumes at 1.8 Ga and earlier which produced pervasive focused melt flow with remelting of mica-amphibole metasomatites giving continuous REE and LILE enrichment in mantle lithologies from 5.8 to 2.5 GPa.
DS202004-0497
2020
Ashfold, M.N.R., Goss, J.P., Green, B., May, P.W., Newton, M.E., Peaker, C.V.Nitrogen in diamond.Chemical Reviews, Vol. 120, 4, 10.1021/ acs.chemrev.9b00578 50p. PdfGlobalHPHT, CVD, synthetics

Abstract: Nitrogen is ubiquitous in both natural and laboratory-grown diamond, but the number and nature of the nitrogen-containing defects can have a profound effect on the diamond material and its properties. An ever-growing fraction of the supply of diamond appearing on the world market is now lab-grown. Here, we survey recent progress in two complementary diamond synthesis methods: high pressure high temperature (HPHT) growth and chemical vapor deposition (CVD), how each is allowing ever more precise control of nitrogen incorporation in the resulting diamond, and how the diamond produced by either method can be further processed (e.g., by implantation or annealing) to achieve a particular outcome or property. The burgeoning availability of diamond samples grown under well-defined conditions has also enabled huge advances in the characterization and understanding of nitrogen-containing defects in diamond alone and in association with vacancies, hydrogen, and transition metal atoms. Among these, the negatively charged nitrogen-vacancy (NV-) defect in diamond is attracting particular current interest in account of the many new and exciting opportunities it offers for, for example, quantum technologies, nanoscale magnetometry, and biosensing.
DS202001-0001
2019
Ashwal, L.D.Wandering continents of the Indian ocean.South African Journal of Geology, Vol. 122, 4, pp. 397-420.IndiaGondwana

Abstract: On the last page of his 1937 book "Our Wandering Continents" Alex Du Toit advised the geological community to develop the field of "comparative geology", which he defined as "the study of continental fragments". This is precisely the theme of this paper, which outlines my research activities for the past 28 years, on the continental fragments of the Indian Ocean. In the early 1990s, my colleagues and I were working in Madagascar, and we recognized the need to appreciate the excellent geological mapping (pioneered in the 1950s by Henri Besairie) in a more modern geodynamic context, by applying new ideas and analytical techniques, to a large and understudied piece of continental crust. One result of this work was the identification of a 700 to 800 Ma belt of plutons and volcanic equivalents, about 450 km long, which we suggested might represent an Andean-type arc, produced by Neoproterozoic subduction. We wondered if similar examples of this magmatic belt might be present elsewhere, and we began working in the Seychelles, where late Precambrian granites are exposed on about 40 of the >100 islands in the archipelago. Based on our new petrological, geochemical and geochronological measurements, we built a case that these ~750 Ma rocks also represent an Andean-type arc, coeval with and equivalent to the one present in Madagascar. By using similar types of approaches, we tracked this arc even further, into the Malani Igneous Province of Rajasthan, in northwest India. Our paleomagnetic data place these three entities adjacent to each other at ~750 Ma, and were positioned at the margins, rather than in the central parts of the Rodinia supercontinent, further supporting their formation in a subduction-related continental arc. A widespread view is that in the Neoproterozoic, Rodinia began to break apart, and the more familiar Gondwana supercontinent was assembled by Pan-African (~500 to 600 Ma) continental collisions, marked by the highly deformed and metamorphosed rocks of the East African Orogen. It was my mentor, Kevin Burke, who suggested that the present-day locations of Alkaline Rocks and Carbonatites (called "ARCs") and their Deformed equivalents (called "DARCs"), might mark the outlines of two well-defined parts of the Wilson cycle. We can be confident that ARCs formed originally in intracontinental rift settings, and we postulated that DARCs represent suture zones, where vanished oceans have closed. We also found that the isotopic record of these events can be preserved in DARC minerals. In a nepheline syenite gneiss from Malawi, the U-Pb age of zircons is 730 Ma (marking the rifting of Rodinia), and that of monazites is 522 Ma (marking the collisional construction of Gondwana). A general outline of how and when Gondwana broke apart into the current configuration of continental entities, starting at about 165 Ma, has been known for some time, because this record is preserved in the magnetic properties of ocean-floor basalts, which can be precisely dated. A current topic of active research is the role that deep mantle plumes may have played in initiating, or assisting, continental fragmentation. I am part of a group of colleagues and students who are applying complementary datasets to understand how the Karoo (182 Ma), Etendeka (132 Ma), Marion (90 Ma) and Réunion (65 Ma) plumes influenced the break-up of Gondwana and the development of the Indian Ocean. Shortly after the impingement of the Karoo plume at 182 Ma, Gondwana fragmentation began as Madagascar + India + Antarctica separated from Africa, and drifted southward. Only after 90 Ma, when Madagascar was blanketed by lavas of the Marion plume, did India begin to rift, and rapidly drifted northward, assisted by the Marion and Deccan (65 Ma) plumes, eventually colliding with Asia to produce the Himalayas. It is interesting that a record of these plate kinematics is preserved in the large Permian - Eocene sedimentary basins of western Madagascar: transtensional pull-apart structures are dextral in Jurassic rocks (recording initial southward drift with respect to Africa), but change to sinistral in the Eocene, recording India’s northward drift. Our latest work has begun to reveal that small continental fragments are present in unexpected places. In the young (max. 9 Ma) plume-related, volcanic island of Mauritius, we found Precambrian zircons with ages between 660 and 3000 Ma, in beach sands and trachytic lavas. This can only mean that a fragment of ancient continent must exist beneath the young volcanoes there, and that the old zircons were picked up by ascending magmas on their way to surface eruption sites. We speculate, based on gravity inversion modelling, that continental fragments may also be present beneath the Nazareth, Saya de Malha and Chagos Banks, as well as the Maldives and Laccadives. These were once joined together in a microcontinent we called “Mauritia”, and became scattered across the Indian Ocean during Gondwana break-up, probably by mid-ocean ridge “jumps”. This work, widely reported in international news media, allows a more refined reconstruction of Gondwana, suggests that continental break-up is far more complex than previously perceived, and has important implications for regional geological correlations and exploration models. Our results, as interesting as they may be, are merely follow-ups that build upon the prescient and pioneering ideas of Alex Du Toit, whose legacy I appreciatively acknowledge.
DS202004-0498
2019
Ashwal, L.D.Wandering continents of the Indian Ocean. DARC's.South African Journal of Geology, Vol. 122, 4, pp. 397-420.Indiaalkaline, carbonatites

Abstract: On the last page of his 1937 book “Our Wandering Continents” Alex Du Toit advised the geological community to develop the field of “comparative geology”, which he defined as “the study of continental fragments”. This is precisely the theme of this paper, which outlines my research activities for the past 28 years, on the continental fragments of the Indian Ocean. In the early 1990s, my colleagues and I were working in Madagascar, and we recognized the need to appreciate the excellent geological mapping (pioneered in the 1950s by Henri Besairie) in a more modern geodynamic context, by applying new ideas and analytical techniques, to a large and understudied piece of continental crust. One result of this work was the identification of a 700 to 800 Ma belt of plutons and volcanic equivalents, about 450 km long, which we suggested might represent an Andean-type arc, produced by Neoproterozoic subduction. We wondered if similar examples of this magmatic belt might be present elsewhere, and we began working in the Seychelles, where late Precambrian granites are exposed on about 40 of the >100 islands in the archipelago. Based on our new petrological, geochemical and geochronological measurements, we built a case that these ~750 Ma rocks also represent an Andean-type arc, coeval with and equivalent to the one present in Madagascar. By using similar types of approaches, we tracked this arc even further, into the Malani Igneous Province of Rajasthan, in northwest India. Our paleomagnetic data place these three entities adjacent to each other at ~750 Ma, and were positioned at the margins, rather than in the central parts of the Rodinia supercontinent, further supporting their formation in a subduction-related continental arc. A widespread view is that in the Neoproterozoic, Rodinia began to break apart, and the more familiar Gondwana supercontinent was assembled by Pan-African (~500 to 600 Ma) continental collisions, marked by the highly deformed and metamorphosed rocks of the East African Orogen. It was my mentor, Kevin Burke, who suggested that the present-day locations of Alkaline Rocks and Carbonatites (called “ARCs”) and their Deformed equivalents (called “DARCs”), might mark the outlines of two well-defined parts of the Wilson cycle. We can be confident that ARCs formed originally in intracontinental rift settings, and we postulated that DARCs represent suture zones, where vanished oceans have closed. We also found that the isotopic record of these events can be preserved in DARC minerals. In a nepheline syenite gneiss from Malawi, the U-Pb age of zircons is 730 Ma (marking the rifting of Rodinia), and that of monazites is 522 Ma (marking the collisional construction of Gondwana). A general outline of how and when Gondwana broke apart into the current configuration of continental entities, starting at about 165 Ma, has been known for some time, because this record is preserved in the magnetic properties of ocean-floor basalts, which can be precisely dated. A current topic of active research is the role that deep mantle plumes may have played in initiating, or assisting, continental fragmentation. I am part of a group of colleagues and students who are applying complementary datasets to understand how the Karoo (182 Ma), Etendeka (132 Ma), Marion (90 Ma) and Réunion (65 Ma) plumes influenced the break-up of Gondwana and the development of the Indian Ocean. Shortly after the impingement of the Karoo plume at 182 Ma, Gondwana fragmentation began as Madagascar + India + Antarctica separated from Africa, and drifted southward. Only after 90 Ma, when Madagascar was blanketed by lavas of the Marion plume, did India begin to rift, and rapidly drifted northward, assisted by the Marion and Deccan (65 Ma) plumes, eventually colliding with Asia to produce the Himalayas. It is interesting that a record of these plate kinematics is preserved in the large Permian - Eocene sedimentary basins of western Madagascar: transtensional pull-apart structures are dextral in Jurassic rocks (recording initial southward drift with respect to Africa), but change to sinistral in the Eocene, recording India’s northward drift. Our latest work has begun to reveal that small continental fragments are present in unexpected places. In the young (max. 9 Ma) plume-related, volcanic island of Mauritius, we found Precambrian zircons with ages between 660 and 3000 Ma, in beach sands and trachytic lavas. This can only mean that a fragment of ancient continent must exist beneath the young volcanoes there, and that the old zircons were picked up by ascending magmas on their way to surface eruption sites. We speculate, based on gravity inversion modelling, that continental fragments may also be present beneath the Nazareth, Saya de Malha and Chagos Banks, as well as the Maldives and Laccadives. These were once joined together in a microcontinent we called "Mauritia", and became scattered across the Indian Ocean during Gondwana break-up, probably by mid-ocean ridge "jumps". This work, widely reported in international news media, allows a more refined reconstruction of Gondwana, suggests that continental break-up is far more complex than previously perceived, and has important implications for regional geological correlations and exploration models. Our results, as interesting as they may be, are merely follow-ups that build upon the prescient and pioneering ideas of Alex Du Toit, whose legacy I appreciatively acknowledge.
DS202008-1367
2020
Aulbach, S.Temperature dependent rutile solubility in garnet and clinopyroxene from mantle eclogite: implications for continental crust formation and V-based oxybarometry. ( kimberlite)Journal of Petrology, , https://doi.org/10. 1093/petrology/egaa065Mantleoxygen fugacity

Abstract: Despite its accessory mineral status in metabasaltic rocks, rutile controls the whole-rock Ti, Nb and Ta budget. These are key elements used to trace fluid- and melt-mediated mass transfer across the mantle-crust boundary. Rutile also contains significant amounts of the redox-sensitive element V, which is increasingly used to estimate oxygen fugacity. Kimberlite-borne mantle eclogite xenoliths, which are frequently rutile-bearing, have been interpreted as residues from the extraction of silicic partial melt similar in composition to the average continental crust. Published mineral compositions for eclogite xenoliths from various cratons combined with geothermobarometrical calculations show that TiO2 contents in garnet and clinopyroxene increase with increasing temperature of last residence in the lithospheric mantle, while apparent clinopyroxene-garnet distribution coefficients decrease. This implies that (1) increasing TiO2 contents in eclogitic garnet or clinopyroxene are not a signature of increasing metasomatism with depth, (2) whole-rock eclogites reconstructed without rutile will increasingly underestimate TiO2, Nb and Ta contents with decreasing temperature, and (3) low-temperature eclogites are more likely to contain free rutile. Only about a third of the ?250 samples considered here would have whole-rock TiO2 contents (reconstructed with calculated rutile modes) required for rutile saturation during subduction and partial melting. If there is a role for subducting oceanic crust now sampled as mantle eclogite, the characteristic Ti-Nb-Ta depletion in continental crust may require fluid-dominated processes, where these elements are not efficiently mobilised.
DS202009-1609
2020
Aulbach, S.Temperature-dependent rutile solubility in garnet and clinopyroxene from mantle eclogite: implications for continental crust formation and V-based oxybarometer.Journal of Petrology, in press available, 89p. PdfMantleeclogite

Abstract: Despite its accessory mineral status in metabasaltic rocks, rutile controls the whole-rock Ti, Nb and Ta budget. These are key elements used to trace fluid- and melt-mediated mass transfer across the mantle-crust boundary. Rutile also contains significant amounts of the redox-sensitive element V, which is increasingly used to estimate oxygen fugacity. Kimberlite-borne mantle eclogite xenoliths, which are frequently rutile-bearing, have been interpreted as residues from the extraction of silicic partial melt similar in composition to the average continental crust. Published mineral compositions for eclogite xenoliths from various cratons combined with geothermobarometrical calculations show that TiO2 contents in garnet and clinopyroxene increase with increasing temperature of last residence in the lithospheric mantle, while apparent clinopyroxene-garnet distribution coefficients decrease. This implies that (1) increasing TiO2 contents in eclogitic garnet or clinopyroxene are not a signature of increasing metasomatism with depth, (2) whole-rock eclogites reconstructed without rutile will increasingly underestimate TiO2, Nb and Ta contents with decreasing temperature, and (3) low-temperature eclogites are more likely to contain free rutile. Only about a third of the ?250 samples considered here would have whole-rock TiO2 contents (reconstructed with calculated rutile modes) required for rutile saturation during subduction and partial melting. If there is a role for subducting oceanic crust now sampled as mantle eclogite, the characteristic Ti-Nb-Ta depletion in continental crust may require fluid-dominated processes, where these elements are not efficiently mobilised.
DS202004-0499
2020
Aulbach, S., Masuyeau, M., Gerdes, A., Garber, J.M.Ultramafic carbonated melt- and-auto -metasomatism in mantle eclogites: compositional effects and geophysical consequences.Geochemistry, Geophysics, Geosystems, in press available, 41p. PdfMantleeclogites
DS202006-0909
2020
Aulbach, S., Symes, C., Chacko, T.Elemental and radiogenic isotope perspective on formation and transformation of cratonic lower crust: Central Slave craton ( Canada).Geochimica et Cosmochimica Acta, Vol. 278, pp. 78-83.Canada, Northwest Territorieskimberlites

Abstract: Kimberlite-borne granulite xenoliths provide rare insights into the age, chemical composition and tectonothermal evolution of the otherwise largely inaccessible deep cratonic crust. The formation and transformation of the lower continental crust (LCC) beneath the central Slave craton (Canada) is here illuminated using whole-rock trace-element and Sr-Nd isotope compositions of nine metabasaltic (MBG), one gabbroic (MGG) and two metasedimentary/hybrid (MSG) granulite xenoliths. On the one hand, published sulphide Re-Os and a few zircon U-Pb data indicate that at least a portion of the LCC beneath the central Slave craton has a Palaeoarchaean origin (?3.3?Ga), which apparently coincides with a period of juvenile crust and deep lithospheric mantle formation during plume impingement beneath the pre-existing cratonic nucleus. On the other hand, enrichment in Li, Sr, LREE, Pb and Th, but relative depletion in Ti, Hf and HREE, suggest formation of (picro)basaltic protoliths by partial melting of a subduction-modified garnet-bearing source, Crystallisation in the crust after fractionation of plagioclase is inidicated by their Sr and Eu negative anomalies, which are complementary to the positive anomalies in the MGG. Samarium-Nd isotopes in MBG and MGG show large scatter, but fall on Neo- or Mesoarchaean age arrays. These elemental systematics are suggested to fingerprint deserpentinisation fluids plus small amounts of sedimentary melt as the main contaminants of the mantle source, supporting the operation of at least regional and transient subduction at 3.3?Ga. Evidence for quasi-coeval plume impingement and subduction beneath the central Slave craton in the Mesoarchaean is reconcilable in a dynamic regime where vertical tectonics, though waning, was still active and plate interactions became increasingly important. Unradiogenic 87Sr/86Sr (down to 0.7017) is consistent with significant loss of Rb and probably other heat-producing elements (K, Th, U) plus H2O during Neoarchaean metamorphism, which helped to enhance LCC viscosity and stabilise the cratonic lithosphere.
DS202006-0910
2020
Aulbach, S., Viljoen, K.S., Gerdes, A.Diamondiferous and barren eclogites and pyroxenites from the western Kaapvaal craton record subduction processes and mantle metasomatism respectively.Lithos, in press available 52p. PdfAfrica, South Africadeposit - Doomkloof-Sover

Abstract: Mineral major and trace elements combined with Sr isotopes of clinopyroxene are used to unravel the origins and evolution of mantle eclogite and pyroxenite xenoliths from the Doornkloof-Sover orangeite dike (western Kaapvaal craton), and to investigate the generation and destruction of diamond in these rocks. Two different eclogite types are present: (1) MgO-poor eclogites (MgO?=?7.3 to 14.5?wt%; n?=?43) with accessory diamond ± corundum and kyanite; garnet grossular content (median Ca#?=?0.25) and clinopyroxene jadeite content (0.39). Reconstructed bulk rocks are LREE-depleted (median La 0.29?ppm) and have low median Cr2O3 (0.06?wt%) and incompatible trace-element contents (e.g. Sr, Zr, Ba, Pb, Th), and high Li and transition metal abundances. Some are characterised by stepped REE patterns or steep slopes in the MREE, similar to eclogites affected by interaction with dehydration fluids generated in subduction zones. These fluids may also have deposited diamond in typically reducing eclogite assemblages at diamond-stable pressures. (2) MgO-rich eclogites and pyroxenites (MgO?=?14.0 to 20.0?wt%; n?=?29), which are barren and enriched in LREE (median La 1.39?ppm), Cr2O3 (0.25?wt%) and incompatible trace elements, with lower Li and transition metal abundances than the MgO-poor group. These are typical signatures of carbonated ultramafic melt metasomatism in the mantle lithosphere. Strontium isotopic compositions vary widely in both groups, but high Cr2O3 and Ba contents are dominantly associated with 87Sr/86Sr?>?0.7055. This reflects interaction with metasomatic agents remobilised from ancient lithospheric metasomes, which eventually gave rise to regional orangeite magmatism. The presence of strong positive Eu anomalies in both groups, including two pyroxenites, requires low-pressure igneous protoliths, presumably derived from a ca. 3?Ga spreading ridge, as reported for other eclogite materials from the western Kaapvaal craton. Based on the proportions of MgO-poor and -rich eclogites and pyroxenites, approximately 40% of the diamond inventory were destroyed by mantle metasomatism centred at ~135?±?15?km depth, overlapping a low-velocity anomaly (mid-lithospheric discontinuity). Two diamondiferous orangeites ?20?km from Doornkloof-Sover contain significantly different eclogite xenolith populations: At Newlands, MgO-poor diamondiferous eclogites are present in addition to barren MgO-rich ones and pyroxenite, suggesting that the host orangeite sampled a source region equally affected by diamond-destructive mantle metasomatism, whereas at Bellsbank, all eclogites are MgO-poor and LREE-depleted. This may explain higher diamond grades reported for this locality compared to Newlands or Doornkloof-Sover.
DS202008-1368
2019
Aulbach, S., Woodand, A.B., Stern, R.A., Vasileyev, P., Heaman, L.M., Viljoen, K.S.Evidence for a dominantly reducing Archean ambient mantle from two redox proxies, and low oxygen fugacity of deeply subducted oceanic crust. Nature Research Scientific Reports, Vol. 9:20190 doir.org/10.38 /s41598-019-55743-1, 11p. PdfMantleeclogite

Abstract: Oxygen fugacity (ƒO2) is an intensive variable implicated in a range of processes that have shaped the Earth system, but there is controversy on the timing and rate of oxidation of the uppermost convecting mantle to its present ƒO2 around the fayalite-magnetite-quartz oxygen buffer. Here, we report Fe3+/?Fe and ƒO2 for ancient eclogite xenoliths with oceanic crustal protoliths that sampled the coeval ambient convecting mantle. Using new and published data, we demonstrate that in these eclogites, two redox proxies, V/Sc and Fe3+/?Fe, behave sympathetically, despite different responses of their protoliths to differentiation and post-formation degassing, seawater alteration, devolatilisation and partial melting, testifying to an unexpected robustness of Fe3+/?Fe. Therefore, these processes, while causing significant scatter, did not completely obliterate the underlying convecting mantle signal. Considering only unmetasomatised samples with non-cumulate and little-differentiated protoliths, V/Sc and Fe3+/?Fe in two Archaean eclogite suites are significantly lower than those of modern mid-ocean ridge basalts (MORB), while a third suite has ratios similar to modern MORB, indicating redox heterogeneity. Another major finding is the predominantly low though variable estimated ƒO2 of eclogite at mantle depths, which does not permit stabilisation of CO2-dominated fluids or pure carbonatite melts. Conversely, low-ƒO2 eclogite may have caused efficient reduction of CO2 in fluids and melts generated in other portions of ancient subducting slabs, consistent with eclogitic diamond formation ages, the disproportionate frequency of eclogitic diamonds relative to the subordinate abundance of eclogite in the mantle lithosphere and the general absence of carbonate in mantle eclogite. This indicates carbon recycling at least to depths of diamond stability and may have represented a significant pathway for carbon ingassing through time.
DS202002-0161
2019
Aulbach, S., Woodland, A.B., Stern, R.A., Vasilyev, P., Heaman, L.M., Viljoen, K.S.Evidence for a dominantly reducing Archaean ambient mantle from two redox proxies, and low oxygen fugacity of deeply subducted oceanic crust.Nature Research Scientific Reports, https://doi.org/10.1038/ s41598-019-55743-1 11p. PdfMantlemelting, redox

Abstract: Privacy Policy. You can manage your preferences in 'Manage Cookies'. Oxygen fugacity (fO2) is an intensive variable implicated in a range of processes that have shaped the Earth system, but there is controversy on the timing and rate of oxidation of the uppermost convecting mantle to its present fO2 around the fayalite-magnetite-quartz oxygen buffer. Here, we report Fe3+/?Fe and ƒf2 for ancient eclogite xenoliths with oceanic crustal protoliths that sampled the coeval ambient convecting mantle. Using new and published data, we demonstrate that in these eclogites, two redox proxies, V/Sc and Fe3+/?Fe, behave sympathetically, despite different responses of their protoliths to differentiation and post-formation degassing, seawater alteration, devolatilisation and partial melting, testifying to an unexpected robustness of Fe3+/?Fe. Therefore, these processes, while causing significant scatter, did not completely obliterate the underlying convecting mantle signal. Considering only unmetasomatised samples with non-cumulate and little-differentiated protoliths, V/Sc and Fe3+/?Fe in two Archaean eclogite suites are significantly lower than those of modern mid-ocean ridge basalts (MORB), while a third suite has ratios similar to modern MORB, indicating redox heterogeneity. Another major finding is the predominantly low though variable estimated fO2 of eclogite at mantle depths, which does not permit stabilisation of CO2-dominated fluids or pure carbonatite melts. Conversely, low-fO2 eclogite may have caused efficient reduction of CO2 in fluids and melts generated in other portions of ancient subducting slabs, consistent with eclogitic diamond formation ages, the disproportionate frequency of eclogitic diamonds relative to the subordinate abundance of eclogite in the mantle lithosphere and the general absence of carbonate in mantle eclogite. This indicates carbon recycling at least to depths of diamond stability and may have represented a significant pathway for carbon ingassing through time.
DS202004-0500
2020
Ba, M.H., Ibough, H., Lo, K., Youbi, N., Jaffal, M., Ernst, R.E., Niang, A.J., Dia, I., Abdeina, E.H., Bensalah, M.K., Boumehdi, M.A., Soderlund, U.Spatial and temporal distribution patterns of Precambrian mafic dyke swarms in northern Mauritania ( West African Craton): analysis and results fro remote sensing interpretation, geographical information systems ( GIS), Google Earth TM images, and regionaArabian Journal of Geosciences, Vol. 13, , 209 orchid.org/ 0000-002-3287-9537Africa, Mauritaniacraton

Abstract: We used remote sensing, geographical information systems, Google Earth™ images, and regional geology in order to (i) improve the mapping of linear structures and understand the chronology of different mafic dyke swarms in the Ahmeyim area that belongs to the Archean Tasiast-Tijirit Terrane of the Reguibat Shield, West African craton, NW Mauritania. The spatial and temporal distributions with the trends of the dyke swarms provide important information about geodynamics. The analysis of the mafic dyke swarms map and statistical data allow us to distinguish four mafic dyke swarm sets: a major swarm trending NE-SW to NNE-SSW (80%) and three minor swarms trending EW to ENE-WSW (9.33%), NW-SE to WNW-ESE (9.06%), and NS (1.3%). The major swarms extend over 35 km while the minor swarms do not exceed 13 km. The Google Earth™ images reveal relative ages through crossover relationships. The major NE-SW to NNE-SSW and the minor NS swarms are the oldest generations emplaced in the Ahemyim area. The NW-SE-oriented swarm dykes which are cutting the two former swarms are emplaced later. The minor E-W to WSW-ENE swarms are probably the youngest. A precise U-Pb baddeleyite age of 2733?±?2 Ma has been obtained for the NNE-SSW Ahmeyim Great Dyke. This dyke is approximately 1500 m wide in some zone and extends for more than 150 km. The distinct mafic dyke swarms being identified in this study can potentially be linked with coeval magmatic events on other cratons around the globe to identify reconstructed LIPs and constrain continental reconstructions.
DS202003-0330
2019
Badukhinov, L.D., Spetius, Z.V.. Kislov, E.V., Ivanov, A.S., Monkhorov, R.V.Parageneses of garnet inclusions in diamonds from Yakutia kimberlites based on Raman and IR spectroscopy data. Udachnaya, Zapolyarnaya, Komolskaya, Yuibeyana, Aikhal, Mir, Mayskaya.Geology of Ore Deposits, Vol. 61, 7, pp. 606-612. pdfRussia, Yakutiadiamond inclusions
DS202001-0002
2019
Ball, P.Black diamonds.Nature Materials, Vol. 18, pp. 1266-1277.Globalnanodiamond
DS202002-0162
2020
Barras, C.New signs of a shielding magnetic field found in Earth's oldest rock crystals ( zircons) Tarduno researcherScience, doi:101126/science.aba9499Mantlegeophysics - magnetics
DS202001-0003
2019
Barron, L.M., Barron, B.J., Sutherland, F.L.Re-appraisal of published nitrogen aggregation results in diamonds from Copeton, New South Wales.Australian Journal of Earth Sciences, Vol. 67, 1, pp. 151-152.Australia, New South Walesdeposit - Copeton
DS202009-1610
2020
Bassoo, R., Befus, K.S., Liang, P., Forman, S.L., Sharman, G.Deciphering the enigmatic origin of Guyana's diamonds.The American Mineralogist, in press available 59p. PdfSouth America, Guyanadiamond crystallography

Abstract: Diamonds have long been mined from alluvial terrace deposits within the rainforest of Guyana, South America. No primary kimberlite deposits have been discovered in Guyana, nor has there been previous studies on the mineralogy and origin of the diamonds. Paleoproterozoic terranes in Guyana are prospective to diamond occurrences because the most productive deposits are associated spatially with the eastern escarpment of the Paleoproterozoic Roraima Supergroup. Geographic proximity suggests that the diamonds are detrital grains eroding from the <1.98 Ga conglomerates, metamorphosed to zeolite and greenschist facies. The provenance and paragenesis of the alluvial diamonds are described using a suite of placer diamonds from different locations across the Guiana Shield. Guyanese diamonds are typically small, and those in our collection range from 0.3 to 2.7 mm in diameter; octahedral and dodecahedral, with lesser cubic and minor macle forms. The diamonds are further subdivided into those with abraded and non-abraded surfaces. Abraded diamonds show various colors in cathodoluminescence whereas most non-abraded diamonds appear blue. In all populations, diamonds are predominantly colorless, with lesser brown to yellow and very rare white. Diamonds are predominantly Type IaAB and preserve moderate nitrogen aggregation and total nitrogen concentrations ranging from trace to ~1971 ppm. The kinetics of nitrogen aggregation indicate mantle-derived residence temperatures of 1124 ± 100 ºC, assuming residence times of 1.3 Ga and 2.6 Ga for abraded and non-abraded diamonds respectively. The diamonds are largely sourced from the peridotitic to eclogitic lithospheric upper mantle based on both ?13C values of -5.82 ± 2.45‰ (VPDB-LSVEC) and inclusion suites predominantly comprised of forsterite, enstatite, Cr-pyrope, chromite, rutile, clinopyroxene, coesite, and almandine garnet. Detrital, accessory minerals are non-kimberlitic. Detrital zircon geochronology indicates diamondiferous deposits are predominantly sourced from Paleoproterozoic rocks of 2079 ± 88 Ma.
DS202012-2204
2020
Bassoo, R., Refus, K.S.Finders Keepers: Crater of Diamonds Gems & Gemology, Vol. 56, 2, summer pp. 311-314. United States, Arkansasdeposit - Crater of diamonds

Abstract: There’s only one place on earth where the general public can prospect for diamonds directly from a primary kimberlite pipe: Crater of Diamonds State Park. This park is nestled among the pines, 100 miles off the interstate near the town of Murfreesboro, Arkansas. It boasts a network of scenic walking trails, picnic sites, and campsites. At its Diamond Discovery Center, visitors can learn about the local geology. Staff are also on hand to identify any minerals that are taken home, per their "finders, keepers" policy. The park is an ideal spot for a field trip. The state also hosts many other unusual igneous rocks, including carbonatite, lamprophyre, and lamproite. With this in mind, our university petrology class piled into a van to visit Arkansas and learn about mantle-derived magmas and associated volcanism. As a side quest, we wanted to try prospecting.
DS202005-0720
2019
Bateman , M.The Handbook of Luminescence Dating. ...dating techniques, including optically and infrared simulated luminescence and thermoluminescence applications.Whiitles Publishing Dunbeith Scotland ( Reviewed in Geoscience Canada Vol. 46, pp. 195-196., 416p. $ 163.00 GlobalLuminescence

Abstract: Luminescence dating is now widely applied by scientists working in Quaternary geology and archaeology to obtain ages for events as diverse as past earthquakes, desertification and cave occupation sites. Using quartz or feldspar minerals found in almost ubiquitous sand and finer sediments, luminescence can provide ages from over 500,000 years ago to modern. Written by some of the foremost experts in luminescence dating from around the world, this book takes a new approach. It explains what luminescence can and can’t do, what and where to sample, types of measurements available and how to interpret and analyse ages once they are measured. It is accordingly for scientists who require luminescence ages for their research rather than those scientists developing the luminescence technique or making their own luminescence measurements. The background to the technique is explained in simple terms so that the range of potential applications, limits and issues can be understood. The book helps scientists plan where and what to sample to optimise the successful application of luminescence and stemming from that the chronologies that can be constructed. The Handbook sets out the challenges and limitations when applying luminescence dating in different environmental and archaeological settings and gives practical advice on how issues might be avoided in sampling, or mitigated by requesting different laboratory measurement approaches or analysis. Guidance is provided on how luminescence ages can be interpreted and published as well as how they can be used within chronological frameworks. With luminescence dating continuing to develop, information on more experimental approaches is given which may help expand the range of chronological challenges to which luminescence dating can be routinely applied
DS202006-0911
2020
Baudouin, C., France, L., Boulanger, M., Dalou, C., Devidal, J-L.Trace element partitioning between clinopyroxene and alkaline magmas: parametrization and role of M1 site on HREE enrichment in clinopyroxenes.Contributions to Mineralogy and Petrology, Vol. 175, 15p. PdfAfrica, Tanzaniadeposit - Oldoinyo Lengai

Abstract: Trace element partitioning between minerals and liquids provides crucial constraints on igneous processes. We quantified trace element concentrations in clinopyroxene (Cpx) phenocrysts and their phonolite melt inclusions from the 2007-08 eruption of Oldoinyo Lengai (Tanzania), and report Cpx-melt partition coefficients (D) and corresponding partitioning equations for rare earth elements (REE) and high field strength elements (HFSE) in alkaline magmas. Heavy REE (HREE: Er, Tm, Yb, Lu) are enriched relative to middle REE in alkaline Cpx and display a specific partitioning behavior that is characteristic of alkaline systems. HFSE (Ti, Zr, Hf) and HREE have similar D values (DHf?=?0.25; DLu?=?0.4) that are significantly higher than MREE (DSm?=?0.06). High DHREE/DMREE are strongly correlated with the high values of DZr and DHf relative to the low DMREE values. In this study, REE partitioning between phonolite melt and Cpx is not consistent with standard models assuming incorporation of all REE in the Cpx M2 site, but rather highlights HREE substitution in both the M1 and M2 sites. Here we highlight the preferential incorporation of HREE in the VI-coordinated M1 site, whereas light REE and MREE remain mostly distributed in the VIII-coordinated M2 site. REE partitioning is strongly dependent on Cpx chemistry: the ideal ionic radius and HREE incorporation in the M1 site increase with increasing Fe3+ content and decrease with increasing Mg2+ and AlVI content. In our study, we focus on alkaline evolved magmas, and update existing models to obtain adequate DHREE for alkaline evolved melts. We provide equations to quantify REE and HFSE partitioning, and HREE enrichment in Cpx that are based on Cpx major element composition and temperature. We propose a new model based on the lattice strain approach that predicts HREE partitioning between Cpx and alkaline magmas. The knowledge of the melt composition or of the trace element contents is not required to obtain DREE from the new model. An improved parameterization of HFSE partitioning between Cpx and phonolite and trachy-phonolite melts is also provided herein. We discuss the potential implications of the new data on our understanding of REE deposits that are commonly associated with igneous alkaline complexes.
DS202005-0721
2020
Bauer, A.M., Reimink, J.R., Chacko, T., Foley, B.J., Shirey, S.B., Pearson, D.G.Hafnium isotopes in zircons document the gradual onset of mobile-lid tectonics. ( Pilbara, Zimbabwe, Slave, Singhbhum, Rae, Wyoming, Jack HillsGeochemical Perspectives Letters, Vol. 14, pp. 1-6.GlobalTectonics

Abstract: The tectonic regime of the early Earth has proven enigmatic due to a scarcity of preserved continental crust, yet how early continents were generated is key to deciphering Earth’s evolution. Here we show that a compilation of data from 4.3 to 3.4 Ga igneous and detrital zircons records a secular shift to higher 176Hf/177Hf after ~3.8-3.6 Ga. This globally evident shift indicates that continental crust formation before ~3.8-3.6 Ga largely occurred by internal reworking of long-lived mafic protocrust, whereas later continental crust formation involved extensive input of relatively juvenile magmas, which were produced from rapid remelting of oceanic lithosphere. We propose that this secular shift in the global hafnium isotope record reflects a gradual yet widespread transition from stagnant-lid to mobile-lid tectonics on the early Earth.
DS202004-0501
2020
BBC NewsDiamond samples in Canada reveal size of lost continent. Chidliak and UBC Kopylovabbc.com, March 20, 1/2p.Canada, Baffin Islandcraton
DS202002-0163
2019
Beard, C.D., van Hinsberg, V.J., Stix, J., Wilke, M.Clinopyroxene melt trace element partitioning in sodic alkaline magmas.Journal of Petrology, in press available 92p. PdfEurope, Canary IslandsREE

Abstract: Clinopyroxene is a key fractionating phase in alkaline magmatic systems, but its impact on metal enrichment processes, and the formation of REE + HFSE mineralisation in particular, is not well understood. To constrain the control of clinopyroxene on REE + HFSE behaviour in sodic (per)alkaline magmas, a series of internally heated pressure vessel experiments was performed to determine clinopyroxene-melt element partitioning systematics. Synthetic tephriphonolite to phonolite compositions were run H2O-saturated at 200?MPa, 650-825?C with oxygen fugacity buffered to log f O2 ? ?QFM + 1 or log f O2 ? ?QFM +5. Clinopyroxene-glass pairs from basanitic to phonolitic fall deposits from Tenerife, Canary Islands, were also measured to complement our experimentally-derived data set. The REE partition coefficients are 0.3-53, typically 2-6, with minima for high-aegirine clinopyroxene. Diopside-rich clinopyroxenes (Aeg5-25) prefer the MREE and have high REE partition coefficients (DEuup to 53, DSmup to 47). As clinopyroxene becomes more Na- and less Ca-rich (Aeg25-50), REE incorporation becomes less favourable, and both the VIM1 and VIIIM2 sites expand (to 0.79 Å and 1.12 Å), increasing DLREE/DMREE. Above Aeg50 both M sites shrink slightly and HREE (VIri? 0.9 Å ? Y) partition strongly onto the VIM1 site, consistent with a reduced charge penalty for REE3+ ? Fe3+ substitution. Our data, complemented with an extensive literature database, constrain an empirical model that predicts trace element partition coefficients between clinopyroxene and silicate melt using only mineral major element compositions, temperature and pressure as input. The model is calibrated for use over a wide compositional range and can be used to interrogate clinopyroxene from a variety of natural systems to determine the trace element concentrations in their source melts, or to forward model the trace element evolution of tholeiitic mafic to evolved peralkaline magmatic systems.
DS202002-0164
2020
Belley, P.M., Groat, L.A.Metamorphosed carbonate platforms and controls on the genesis of sapphire, gem spinel, and lapis Lazuli: insight from the Lake Harbour Group, Nunavut, Canada and implications for gem exploration.Ore Geology Reviews, Vol. 116, 10p. PdfCanada, Nunavutgemstones

Abstract: Baffin Island's Lake Harbour Group (LHG), a Paleoproterozoic granulite facies metasedimentary sequence rich in carbonates, contains occurrences of the gemstones sapphire (corundum), spinel (including vivid blue, cobalt-enriched spinel), and lapis lazuli (haüyne-bearing rock). Most occurrences of these gem minerals are uniquely metasedimentary (carbonates and calc-silicate rock), while a few spinel occurrences formed from metasomatic reactions between Si-Al-rich rock (syenogranite or gneiss) and marble. The metasedimentary corundum, spinel, and haüyne occurrences have similar protoliths: primarily dolomitic marls with a high Al/Si relative abundance (interpreted as sandy mud to clay siliciclastic fraction in the protolith). Kimmirut-type sapphire deposits formed via a multi-step metamorphic process under three different and specific P-T conditions. Lapis lazuli formation required the presence of evaporites to provide Na and possibly S for the blue mineral haüyne. In addition to high Al/Si calc-silicate rocks, spinel also occurs in impure dolomitic marbles with very low K/Al. Potential for Kimmirut-type sapphire deposits is expected to be restricted to metacarbonate sequences proximal to the thrust fault separating the LHG from the Narsajuaq Arc, where retrograde upper amphibolite facies mineralization is most pervasive. Spinel and Kimmirut-type sapphire deposits are expected to be found in dolomitic marble sequences rich in calc-silicate layers. The potential occurrence of lapis lazuli is more difficult to predict but deposits could be identified thanks to large geographical footprints and their color. Similar gem occurrences or deposits to those in the LHG may be found in other metacarbonate-bearing terranes with similar metamorphic conditions (and for Kimmirut-type sapphire, a similar metamorphic history). Aerial hyperspectral and photographic surveys are well-suited to gemstone exploration on southern Baffin Island thanks to excellent rock exposure with minimal sediment or plant/lichen cover. Spectral mapping of dolomite-, diopside-, phlogopite-, and scapolite-rich domains in LHG metacarbonate sequences using airborne hyperspectral data is expected to provide exploration targets. Remote sensing exploration could be used in other metacarbonate-bearing, upper amphibolite to granulite facies metamorphic terranes found in polar climates, arid climates, or at high elevation in mountainous regions where such rocks are well exposed with minimal vegetative cover.
DS202008-1369
2020
Benoaouda, R., Kraemer, D., Sitnikova, M., Goldmann, S., Schwarz-Schampera, U., Errami, A., Mouttaqi, A., Bau, M.Discovery of high grade REE-Nb-Fe mineralization associated with calcio-carbonatite in south Morocco.Ore Geology Reviews, in press available, 43p. PdfAfrica, Moroccocarbonatite

Abstract: The recently discovered REE and Nb mineralization in the Twihinat area in the western part of the Oulad Dlim Massif (Adrar Souttouf) in South Morocco is linked to a Cretaceous calciocarbonatite intrusion which was likely formed in an intracontinental rift setting and crops out locally within a ring structure that mainly consists of massive Fe-oxide mineralization and silica breccia. The carbonatite shows intensively metasomatized zones, which contain bastnaesite and pyrochlore-group minerals as the main REE and Nb ore minerals. They are usually associated with apatite, quartz and Fe-oxides, or trapped in calcite voids, suggesting a secondary ore formation. Within the associated Fe-oxide mineralization, pyrochlore and monazite-(Ce) are the main ore minerals occurring closely associated with quartz and magnetite or hematite. The silica breccia also shows significant subsequent infill of barite, bastnaesite-(Ce) and hydrated ceriopyrochlore, which was identified by EPMA and Raman spectroscopy. Bastnaesite commonly forms prismatic aggregates whereas pyrochlore and ceriopyrochlore usually display subhedral grains along tiny fractures. Structural and textural relationships clearly indicate epigenetic ore formation induced by multiple stages of hydrothermal fluid flow and fracturing. Ore precipitation likely resulted from interaction between low-pH mineralizing hydrothermal fluids and the wall-rock. The latter efficiently buffered the acidity of the fluids and allowed significant amounts of REE and Nb ore minerals to precipitate. Trace element ICP-MS analyses show very high REE and Nb concentrations of up to 0.76 wt% ?REE and 0.21 wt% Nb in carbonatite and up to 3 wt% ?REE and 1.3 wt% Nb in the associated silica and Fe-oxide mineralization. The results clearly demonstrate that the Twihinat REE-Nb deposits are significant and represent a potential new high-grade resource for these critical metals.
DS202007-1125
2020
Berkesi, M., Bali, E., Bodnar, R.J., Szabo, A., Guzmics, T.Carbonatite and highly peralkaline nephelinitie melts from Oldoinyo Lengai volcano, Tanzania: the role of natrite-normative fluid degassing.Gondwana Research, Vol. 85, pp. 76-83. pdfAfrica, Tanzaniadeposit - Oldoinyo Lengai

Abstract: Oldoinyo Lengai, located in the Gregory Rift in Tanzania, is a world-famous volcano owing to its uniqueness in producing natrocarbonatite melts and because of its extremely high CO2 flux. The volcano is constructed of highly peralkaline [PI = molar (Na2O + K2O)/Al2O3 > 2-3] nephelinite and phonolites, both of which likely coexisted with carbonate melt and a CO2-rich fluid before eruption. Results of a detailed melt inclusion study of the Oldoinyo Lengai nephelinite provide insights into the important role of degassing of CO2-rich vapor in the formation of natrocarbonatite and highly peralkaline nephelinites. Nepheline phenocrysts trapped primary melt inclusions at 750-800 °C, representing an evolved state of the magmas beneath Oldoinyo Lengai. Raman spectroscopy, heating-quenching experiments, low current EDS and EPMA analyses of quenched melt inclusions suggest that at this temperature, a dominantly natritess-normative, F-rich (7-14 wt%) carbonate melt and an extremely peralkaline (PI = 3.2-7.9), iron-rich nephelinite melt coexisted following degassing of a CO2 + H2O-vapor. We furthermore hypothesize that the degassing led to re-equilibration between the melt and liquid phases that remained and involved 1/ mixing between the residual (after degassing) alkali carbonate liquid and an F-rich carbonate melt and 2/ enrichment of the coexisting nephelinite melt in alkalis. We suggest that in the geological past similar processes were responsible for generating highly peralkaline silicate melts in continental rift tectonic settings worldwide.
DS202002-0165
2019
Bezada, M.J., Smale, J.Lateral variations in lithospheric mantle structure control the location of intracontinental seismicity in Australia.Geophysical Research Letters, Vol. 46, 22, pp. 12862-12869.Australiageophysics - seismic

Abstract: Despite decades of study, the mechanisms that lead to the localization of intracontinental seismicity remain vigorously debated. We find a very strong correlation between the attenuation of teleseismic P waves and the occurrence of intraplate seismicity in Australia. The regions with the highest attenuation host ~2 orders of magnitude more earthquakes per unit of area than the least attenuating regions. We argue that the attenuation we observe is produced by lateral variations in the thickness and/or viscosity of the lithospheric mantle and further suggest that the correlation we document implies that lithospheric mantle structure exerts first?order controls on the localization of intraplate seismicity.
DS202005-0722
2020
Bhaskar Rao, Y.J., Kumar, T.V., Screeenivas, B., Babu, E.V.S.S.K.A review of Paleo- to Neoarchean crust evolution in the Dharwar craton, southern India and the transition towards a plate tectonic regime.Episodes ( IUGS), Vol. 43, 1, pp. 51-68.Indiacraton

Abstract: An emerging view is that Earth’s geodynamic regime witnessed a fundamental transition towards plate tectonics around 3.0 Ga (billion years). However, the manifestations of this change may have been diachronous and craton-specific. Here, we review geological, geophysical and geochronological data (mainly zircon U-Pb age-Hf isotope compositions) from the Dharwar craton representing over a billion year-long geologic history between ~3.5 and 2.5 Ga. The Archean crust comprises an oblique section of ~12 km from middle to deep crust across low- to mediumgrade granitegreenstone terranes, the Western and Eastern Dharwar Cratons (WDC and EDC), and the highgrade Southern Granulite Terrain (SGT). A segment of the WDC preserving Paleo- to Mesoarchean gneisses and greenstones is characterised by ‘dome and keel’ structural pattern related to vertical (sagduction) tectonics. The geology of the regions with dominantly Neoarchean ages bears evidence for convergent (plate) tectonics. The zircon U-Pb age-Hf isotope data constrain two major episodes of juvenile crust accretion involving depleted mantle sources at 3.45 to 3.17 Ga and 2.7 to 2.5 Ga with crustal recycling dominating the intervening period. The Dharwar craton records clear evidence for the operation of modern style plate tectonics since ~2.7 Ga.
DS202009-1611
2020
Bhaskar Rao, Y.J., Kumar, T.V., Sreenivas, B., Babu, E.V.S.S.K.A review of Paleo to Neoarchean crustal evolution in the Dharwar craton, southern Indian and the transition towards a plate tectonic regime.Episodes, Vol. 43, 1, pp. 51-68.Indiacraton

Abstract: An emerging view is that Earth’s geodynamic regime witnessed a fundamental transition towards plate tectonics around 3.0 Ga (billion years). However, the manifestations of this change may have been diachronous and craton-specific. Here, we review geological, geophysical and geochronological data (mainly zircon U-Pb age-Hf isotope compositions) from the Dharwar craton representing over a billion year-long geologic history between ~3.5 and 2.5 Ga. The Archean crust comprises an oblique section of ~12 km from middle to deep crust across low- to mediumgrade granitegreenstone terranes, the Western and Eastern Dharwar Cratons (WDC and EDC), and the highgrade Southern Granulite Terrain (SGT). A segment of the WDC preserving Paleo- to Mesoarchean gneisses and greenstones is characterised by ‘dome and keel’ structural pattern related to vertical (sagduction) tectonics. The geology of the regions with dominantly Neoarchean ages bears evidence for convergent (plate) tectonics. The zircon U-Pb age-Hf isotope data constrain two major episodes of juvenile crust accretion involving depleted mantle sources at 3.45 to 3.17 Ga and 2.7 to 2.5 Ga with crustal recycling dominating the intervening period. The Dharwar craton records clear evidence for the operation of modern style plate tectonics since ~2.7 Ga.
DS202009-1612
2020
Bidgood, A.K., Parsons, A.J., Lloyd, G.E., Wtares, D.J., Goddard, R.M.EBSD-based criteria for coesite-to-quartz transformation.Journal of Metamorphic Geology, doi.org/10/111/jmg.12566Mantlecoesite

Abstract: Ultrahigh?pressure (UHP) metamorphism observed in continental terranes implies that continental crust can subduct to ~40 kbar before exhuming to the surface. This process is one of the least understood and widely debated parts of the orogenic cycle. The dominantly felsic composition of UHP continental terranes means that many petrology?based techniques for determining peak pressures and temperatures are often not possible. In such cases, the detection of UHP conditions depends on the preservation of coesite, a rarely preserved mineral in exhumed UHP terranes as it rapidly transforms to quartz on decompression. Consequently, the qualitative identification of palisade quartz microstructures that form during the retrograde transformation of coesite to quartz is often used to identify UHP terranes. In this study, we conduct EBSD and misorientation analysis of palisade quartz inclusions in the coesite?bearing pyrope quartzite from the Dora Maira massif in the Alps, and matrix?scale palisade quartz in the Polokongka La granite from Tso Morari in the Ladakh Himalaya, in order to quantitatively define crystallographic characteristics of quartz after coesite. The repeatability of our observations in two unrelated occurrences of UHP rocks supports our interpretation that the following features provide a systematic and predictable set of criteria to identify the coesite to quartz transition: (1) Quartz crystallographic orientations define spatially and texturally distinct subdomains of palisade quartz grains with ‘single crystal’ orientations defined by distinct c?axis point?maxima. (2) Adjacent subdomains are misorientated with respect to each other by a misorientation angle/axis of 90°/. (3) Within each subdomain, palisade quartz grain boundaries commonly have intra? and inter?granular misorientations of 60°/[0001], consistent with the dauphiné twin law. Our observations imply that the coesite?to?quartz transformation is crystallographically controlled by the epitaxial nucleation of palisade quartz on the former coesite grain, specifically on potential coesite twin planes such as (101) and (021).
DS202012-2205
2020
Blaine, J.Kalahari meanderings The Falcinbridge diamond exploration story Botswana 1975-1988. https://youtu.be /07lKCVFT7LE , Oct. ppt presentationAfrica, BotswanaFalconbridge history

Abstract: 22 October 2020 Overberg Geoscientists Group talk by John Blaine
DS202002-0166
2019
Blundy, J.Carbon - beautiful, essential, deadly.Elements, Vol. 15, p. 367 1p.Globalcarbon
DS202006-0912
2020
Bodnar, R.J., Frezzotti, M.L.Microscale chemistry: raman analysis of fluid and melt inclusions.Elements, Vol. 16, pp. 93-98.Mantlemelt inclusions

Abstract: Raman spectroscopy is a commonly applied nondestructive analytical technique for characterizing fluid and melt inclusions. The exceptional spatial resolution (~1 µm) and excellent spectral resolution (?1 cm?1) permits the characterization of micrometer-scale phases and allows quantitative analyses based on Raman spectral features. Data provided by Raman analysis of fluid and melt inclusions has significantly advanced our understanding of complex geologic processes, including preeruptive volatile contents of magmas, the nature of fluids in the deep crust and upper mantle, the generation and evolution of methane-bearing fluids in unconventional hydrocarbon reservoirs. Anticipated future advances include the development of Raman mass spectroscopy and the use of Raman to monitor reaction progress in synthetic and natural fluid inclusion microreactors.
DS202002-0167
2019
Bohm, C.O., Hartlaub, R.P., Heaman, L.M., Cates, N., Guitreau, M., Bourdon, B., Roth, A.S.G., Mojzsis, S.J., Blichert-Toft, J.The Assean Lake Complex: ancient crust at the northwestern margin of the Superior craton, Manitoba, Canada. ( not specific to diamonds)Earth's Oldest Rocks, Chapter 28, 20p. Pdf.Canada, Manitobacraton
DS202012-2206
2020
Borisova, A.Y., Bindeman, I.N., Toplis, M.J., Zagrtdenov, N.R., Guignard, J., Safonov, O.G., Bychkov, A.Y., Shcheka, S., Melnik, O.E., Marcelli, M., Fehrenbach, J.Zircon survival in shallow asthenosphere and deep lithosphere.American Mineralogist, Vol. 105, pp. 1662-1671. pdfMantlemelting

Abstract: Zircon is the most frequently used mineral for dating terrestrial and extraterrestrial rocks. However, the system of zircon in mafic/ultramafic melts has been rarely explored experimentally and most existing models based on the felsic, intermediate and/or synthetic systems are probably not applicable for prediction of zircon survival in terrestrial shallow asthenosphere. In order to determine the zircon stability in such natural systems, we have performed high-temperature experiments of zircon dissolution in natural mid-ocean ridge basaltic and synthetic haplobasaltic melts coupled with in situ electron probe microanalyses of the experimental products at high current. Taking into account the secondary fluorescence effect in zircon glass pairs during electron microprobe analysis, we have calculated zirconium diffusion coefficient necessary to predict zircon survival in asthenospheric melts of tholeiitic basalt composition. The data imply that typical 100 micron zircons dissolve rapidly (in 10 hours) and congruently upon the reaction with basaltic melt at mantle pressures. We observed incongruent (to crystal ZrO2 and SiO2 in melt) dissolution of zircon in natural mid-ocean ridge basaltic melt at low pressures and in haplobasaltic melt at elevated pressure. Our experimental data raise questions about the origin of zircons in mafic and ultramafic rocks, in particular, in shallow oceanic asthenosphere and deep lithosphere, as well as the meaning of the zircon-based ages estimated from the composition of these minerals. Large size zircon megacrysts in kimberlites, peridotites, alkali basalts and other magmas suggest the fast transport and short interaction between zircon and melt.The origin of zircon megacrysts is likely related to metasomatic addition of Zr into mantle as any mantle melting episode should obliterate them.
DS202011-2030
2012
Borst, A.M.The formation and modification of the sub-cratonic lithospheric mantle beneath Botswana. A petrological, geochemical and isotopic study of peridotite xenoliths from the Letlhakane kimberlite mine. *** note dateMsc. Thesis VRIJE University Amsterdam, 166p. Academia available pdfAfrica, Botswanadeposit - Letlhakane

Abstract: The Letlhakane kimberlite pipes are emplaced in the Proterozoic Makondi Fold Belt, Botswana. They belong to a cluster of kimberlite diatremes that also includes the Orapa diamond mine, approximately 40 km to the northwest. In a previous geochemical study on Letlhakane xenoliths it was proposed that the Makondi Fold Belt is underlain by Archaean mantle that belongs to the Zimbabwe Craton. This implies the Letlhakane Kimberlites were sourced from the edge of Zimbabwe cratonic mantle and ascended through Proterozoic Makondi crust, explaining their rather anomalous tectonic setting. In this study we aim to verify the Archaean nature of the lithospheric mantle beneath Letlhakane and assess the origin and extent of metasomatic modifications in comparison to the Kaapvaal and Zimbabwe Cratons. We present an extensive petrological, geochemical and isotopic dataset on a selection of 38 peridotite xenoliths from Letlhakane in order to characterize the mantle that underlies northern Botswana. Whole rock and mineral major and trace elements were measured by electron microprobe (EMP), laser ablation ICPMS and XRF. Sm-Nd and Lu-Hf isotope analyses were performed on garnet, cpx and amphibole separates from 12 selected samples. The sample suite includes spinel harzburgites, spinel lherzolites, a spinel dunite, a wehrlite, a garnet websterite, garnet harzburgites, garnet lherzolites and amphibole bearing garnet lherzolites. The samples are categorized into four groups based on garnet chemistry and modal compositions: I) garnet free samples, II) garnet harzburgites, II) garnet lherzolites and IV) amphibole-bearing garnet lherzolites. Whole rock major elements and olivine magnesium numbers suggest that the SCLM experienced 20 to 60% melt depletion between 5 and 3 GPa. Reconstructed whole rock HREE concentrations and Lu-Yb systematics indicate that up to 20% melting occurred in the absence of garnet, leading to strong fractionation of HREE. The data suggest a shallow decompressional melting regime, consistent with Archaean cratonic genesis models. Preliminary Re-Os data suggest melt depletion occurred at ~2.7 Ga. All samples experienced various amounts of metasomatic re-enrichment expressed by high modal abundances of garnet, opx, clinopyroxene and amphibole. Silica enrichment occurred to a lesser extent than observed in the Kaapvaal, but the Letlhakane samples show significantly more opx-rich assemblages than reported for the Zimbabwe Craton. Sm-Nd and Lu-Hf isotope signatures of garnet harzburgites suggest LREE enrichment occurred around ~2.0 Ga, possibly related to major tectono-magmatic activity associated with accretion of the Makondi Fold Belt to the Zimbabwe Craton. Cpx from the garnet lherzolites show major isotopic interaction and re-equilibration with Group I Kimberlites, which probably crystallized from pre-cursor kimberlitic melts prior to the Letlhakane eruption at ~93 Ma. Trace elements and Nd-Hf istope systematics of the amphibole bearing samples suggest amphibole metasomatism occurred from a LREE, Na, Ka, Ca and Al enriched hydrous melt around 500 to 600 Ma, possibly associated with Pan-African magmatic activity in northern Botswana. The overall lack of negative Nb-Ta anomalies suggests that metasomatic melts were generated in a within-plate geodynamical environment, rather than a subduction related setting.
DS202006-0913
2020
Boxer, G.Grant is teaching workshops for geologists on how to use QGIS - free GIS program - great for students to learn GIS."https://qgisforgeos .thinkific.com/"., GIS programGlobalGIS on line
DS202008-1370
2020
Bracco Gartner, A.J.J., Davies, G.R., Koornneef, J.M.Sub-nanogram Pb isotope analysis of individual melt inclusions.Goldschmidt 2020, 1p. AbstractMantlemagmatism

Abstract: Precise analysis of 20xPb/204Pb ratios is challenging when the amount of Pb is limited by sample volume or elemental concentration. The current precision impedes meaningful analyses of analytes with sub-nanogram Pb contents, such as individual melt inclusions with typical diameters (<100 µm). Decreasing this lower limit whilst maintaining precision and accuracy is crucial for studies aiming to understand the composition and heterogeneity of melt source regions, and the effects of magma transport from the Earth’s interior. The preferred method for precise analysis of sub-nanogram Pb samples combines miniaturised ion-exchange separation, a Pb double spike, and thermal ionisation mass spectrometry (TIMS) with 10^13 ? amplifier technology. This approach allows for interference-free, instrumental mass fractionation-corrected isotope measurements, and therefore provides precision superior to in situ measurements. As a result, reliable analyses can be conducted on samples which contain only a few hundred picograms of Pb. The principal obstacle at the lower limit is the analytical blank, which usually adds a few pg Pb—and thus up to a few percent—to the sample of interest. This contribution may differ for the 207Pb-204Pb-spiked and unspiked runs of one sample, which in turn convolutes the algebraic inversion of the spike. It is therefore imperative to evaluate the magnitude, isotope composition, and homogeneity of the blanks, and constrain how the uncertainty and potential variability within these parameters affect the inversion. Here, we describe the optimised analytical techniques, and discuss the present feasibility and limitations in obtaining precise Pb isotope compositions of rock reference materials and olivine-hosted melt inclusions with sub-nanogram Pb contents. In addition, we discuss the effect of different blank contributions on double-spike analyses using numerical simulations, and evaluate the potential of accurate blank corrections. We find that the optimised technique allows accurate Pb analyses to be conducted on melt inclusions with >200 pg Pb, which will ultimately help to better constrain mantle heterogeneity beneath mid-ocean ridges, oceanic islands, and volcanic arcs.
DS202012-2207
2020
Bradby, J.Diamond bling made within minutes.Sciencetimes.com, https://www.cnn.com /2020/11/19/world/ diamonds-room- temperature-scli -intl-scn/index.html Australiacarbon
DS202002-0168
2020
Braunger, S., Marks, M.A.W., Wenzel, T., Chmyz, L., Azzone, R.G., Markl, G.Do carbonatites and alkaline rocks reflect variable redox conditions in their upper mantle source? ( metasomatism)Earth and Planetary Science Letters, Vol. 533, 11p. PdfMantlecarbonatite

Abstract: A detailed investigation on seven carbonatites and associated alkaline rock complexes (Kaiserstuhl, Sokli, Kovdor, Palabora, Oka, Magnet Cove, Jacupiranga), together with a world-wide comparison between carbonatites, alkaline silicate rocks and mantle xenoliths, implies peculiar redox conditions for carbonatite-bearing alkaline complexes: Carbonatites and associated alkaline rocks in continental settings crystallize from relatively oxidized magmas, on average 1.4 log units () and 1.3 log units () above the synthetic fayalite-magnetite-quartz (FMQ) buffer. In contrast, alkaline rocks in continental settings that lack associated carbonatites reveal rather reduced conditions (mean ; ). The calculated redox conditions for carbonatites and associated silicate rocks demonstrate that these crystallize from relatively oxidized mantle-derived melts compared to the general range found for alkaline rocks in continental settings.
DS202012-2208
2020
Breeding, C.M., Eaton-Magana, S., Shigley, J.E.Naturallly colored yellow and orange gem diamonds: the nitrogen factor.Gems & Gemology, Vol. 56. 2. summer pp. 194-219. pdfGlobalnitrogen

Abstract: Natural yellow gem diamonds are the most common of the fancy-color diamonds, while orange diamonds are among the rarest when they have unmodified hues. Both categories owe their coloration to atomic-level lattice defects associated with nitrogen impurities in the diamond structure. Four major groups of defects are responsible for the color in nearly all yellow and orange diamonds: cape defects (N3 and associated absorptions), isolated nitrogen defects, the 480 nm visible absorption band, and H3 defects. Nitrogen-bearing diamonds are thought to incorporate isolated nitrogen during growth by substitution for carbon, meaning that natural diamonds start out with yellow to orange color. However, only the very rare type Ib diamonds maintain that original color. With time at high temperatures deep in the earth, the nitrogen atoms in most diamonds aggregate, resulting in either near-colorless stones or yellow diamonds colored by cape defects. Yellow and orange diamonds can be grown in a laboratory or created by color treatments, so a thorough understanding of the defects responsible for color in the natural stones is critical for identification. Yellow diamonds serve as the best ambassador to the colored diamond world due to their abundance and may be the only colored diamond many people will ever see in a jewelry store.
DS202009-1613
2020
Brenker, F.E., Nestola, F., Brenker, L., Peruzzo, L., Harris, J.W.Origin, properties and structure of breyite: the second most abundant mineral inclusion in super-deep diamonds. The American Mineralogist, in press available, 21p. PdfMantlebreyite
DS202008-1371
2018
Brook, M.C.The Botswana pipeline - "prospecting to jewellery"Botswana Journal of Earth Sciences, Vol. 7, pp. 43-57. pdfAfrica, Botswanaprospecting, markets

Abstract: In this paper I describe the different components that make up the Botswana Diamond Pipeline today, which means the supply chain of diamonds, that ranges from diamond prospecting to mining, to diamond processing and recovery, to rough diamond sorting, valuation, sales and marketing, to diamond polishing and cutting, and finally to diamond jewellery manufacturing and retail. In Botswana, we can now truly witness the journey of the diamond from “Rough to Finger” or from “Mine to Store” (Fig. 1). Today, Botswana is the world’s second largest producer of diamonds by value and volume after Russia, and there are currently twelve known kimberlite fields (Fig. 2) and eight operating diamond mines. Botswana’s diamonds are cut and polished into beautiful diamond jewellery locally and across the globe.
DS202003-0331
2020
Brooks, K.Perovskite.Geology Today, Vol. 36, 1, pp. 33-38. pdfMantleperovskite

Abstract: How many people, even those interested in the Earth sciences, have heard of perovskite? Yet minerals with the perovskite structure are the most abundant minerals on the Earth with a corresponding importance for our understanding of the origin, development and functioning of our planet. Furthermore, they play important roles in modern technology, including the storage of nuclear waste, in solar cells and as superconductors.
DS202011-2031
2020
Brooks, K.Lithium mineralsGeology Today, Vol. 6, 5, pp. 192-197.Globallithium

Abstract: Lithium is a critical element in modern technology, and lithium minerals will play a key role in the fight against climate change. However, the demand for lithium?ion batteries is dependent on an expanding supply of primary resources. Lithium occurs in limited amounts on the Earth in a surprising diversity of mineral species, from pyroxenes to amphiboles, phyllosilicates to phosphates. This article examines the principal mineral groups likely to be a target for future exploitation.
DS202003-0332
2020
Broom-Fendley, S., Smith, M.P., Andrade, M.B., Ray, S., Banks, D.A., Loye, E., Antencio, D., Pickles, J.P., Wall, F.Sulfur bearing monzazite (Ce) from the Eureka carbonatite, Namibia: oxidation state, substitution mechanism, and formation conditions.Mineralogical Magazine, pp. 1-14, pdfAfrica, Namibiacarbonatite, REE

Abstract: Sulfur-bearing monazite-(Ce) occurs in silicified carbonatite at Eureka, Namibia, forming rims up to ~0.5 mm thick on earlier-formed monazite-(Ce) megacrysts. We present X-ray photoelectron spectroscopy data demonstrating that sulfur is accommodated predominantly in monazite-(Ce) as sulfate, via a clino-anhydrite-type coupled substitution mechanism. Minor sulfide and sulfite peaks in the X-ray photoelectron spectra, however, also indicate that more complex substitution mechanisms incorporating S2 and S4+ are possible. Incorporation of S6+ through clino-anhydrite-type substitution results in an excess of M2+ cations, which previous workers have suggested is accommodated by auxiliary substitution of OH for O2. However, Raman data show no indication of OH, and instead we suggest charge imbalance is accommodated through F substituting for O2. The accommodation of S in the monazite-(Ce) results in considerable structural distortion that may account for relatively high contents of ions with radii beyond those normally found in monazite-(Ce), such as the heavy rare earth elements, Mo, Zr and V. In contrast to S-bearing monazite-(Ce) in other carbonatites, S-bearing monazite-(Ce) at Eureka formed via a dissolutionprecipitation mechanism during prolonged weathering, with S derived from an aeolian source. While large S-bearing monazite-(Ce) grains are likely to be rare in the geological record, formation of secondary S-bearing monazite-(Ce) in these conditions may be a feasible mineral for dating palaeo-weathering horizons.
DS202009-1614
2020
Brovarone, A.V., Butch, C.J., Ciappa, A., Cleaves, H.J., Elmaleh, A., Faccenda, M., Feineman, M., Hermann, J., Nestola, F., Cordone, A., Giovannelli., D.Let there be water: how hydration/dehydration reactions accompany key Earth and life processes.American Mineralogist, Vol. 105, pp. 1152-1160. pdfMantlecarbon

Abstract: Water plays a key role in shaping our planet and making life possible. Given the abundance of water on Earth's surface and in its interior, chemical reactions involving water, namely hydration and dehydration reactions, feature prominently in nature and are critical to the complex set of geochemical and biochemical reactions that make our planet unique. This paper highlights some fundamental aspects of hydration and dehydration reactions in the solid Earth, biology, and man-made materials, as well as their connections to carbon cycling on our planet.
DS202010-1830
2020
Brown, D.A., Tamblyn, R., Hand, M., Morrissey, L.J.Thermobarometric constraints on burial and exhumation of 2 billion year old eclogites and their metapelitic hosts.Precambrian Research, Vol. 347, 105833, 33p. PdfAfrica, Tanzaniaeclogites

Abstract: One of the first appearances of eclogite-facies mineral assemblages in the geological record occurs in the c. 2000 Ma Palaeoproterozoic Usagaran Belt in central Tanzania, where the extended margin of the Tanzanian Craton is interpreted to have been subducted. Mafic rocks are interpreted to have contained the mineral assemblage garnet + omphacite + rutile + quartz ± amphibole. This high-pressure assemblage has been overprinted by a secondary mineral assemblage containing clinopyroxene + plagioclase + hornblende + ilmenite ± orthopyroxene. Mineral equilibria forward modelling indicates that the eclogite-facies assemblages reached minimum peak pressure-temperature (P-T) conditions of ~17 kbar and ~700 °C. Inclusions in garnet document a prograde P-T history consistent with burial through upper amphibolite-facies conditions and possible partial melting. Petrological and compositional evidence from garnet suggests that following peak metamorphism, the eclogite-facies rocks were heated while stalled at approximate peak pressures. Temperature estimates derived from Zr concentrations in interpreted texturally retrograde rutile support a near-isothermal post-peak P-T evolution for the eclogite-facies rocks - an evolution that terminates at retrograde P-T conditions of approximately 7.6-8.2 kbar and 680-790 °C. The relict eclogite domains form part of a larger assemblage with enclosing migmatitic metapelitic lithologies (the Isimani Suite). The metapelitic gneisses contain garnet + kyanite + biotite + staurolite + hornblende + plagioclase + muscovite + rutile + quartz and preserve minimal evidence of a high-pressure history, conceivably due to post-peak mineralogical recrystallisation. P-T modelling, inclusion assemblages and compositional zonation patterns in porphyroblastic garnet suggests the metapelitic gneisses — similarly to the relict eclogites — experienced burial to minimum peak pressures of approximately 16.5-17 kbar. Compositional zoning patterns in eclogitic garnet suggest the Isimani system was buried, reached peak metamorphic conditions, and was subsequently exhumed within a timeframe of up to 20 Myr. A tectonic regime involving crustal thickening and subduction, followed by extensional exhumation of the entire Isimani Suite is our preferred model for the development of the c. 2000 Ma Usagaran Belt.
DS202005-0723
2020
Brown, M., Johnson, T., Gardiner, N.J.Plate tectonics and the Archean Earth.Annual Review of Earth and Planetary Sciences, Vol. 48, 30p. pdfMantlesubduction, metamorphism

Abstract: If we accept that a critical condition for plate tectonics is the creation and maintenance of a global network of narrow boundaries separating multiple plates, then to argue for plate tectonics during the Archean requires more than a local record of subduction. A case is made for plate tectonics back to the early Paleoproterozoic, when a cycle of breakup and collision led to formation of the supercontinent Columbia, and bimodal metamorphism is registered globally. Before this, less preserved crust and survivorship bias become greater concerns, and the geological record may yield only a lower limit on the emergence of plate tectonics. Higher mantle temperature in the Archean precluded or limited stable subduction, requiring a transition to plate tectonics from another tectonic mode. This transition is recorded by changes in geochemical proxies and interpreted based on numerical modeling. Improved understanding of the secular evolution of temperature and water in the mantle are key targets for future research. 1) Higher mantle temperature in the Archean precluded or limited stable subduction, requiring a transition to plate tectonics from another tectonic mode. 2) Plate tectonics can be demonstrated on Earth since the early Paleoproterozoic (since c. 2.2 Ga), but before the Proterozoic Earth's tectonic mode remains ambiguous. 3) The Mesoarchean to early Paleoproterozoic (3.2-2.3 Ga) represents a period of transition from an early tectonic mode (stagnant or sluggish lid) to plate tectonics. 4) The development of a global network of narrow boundaries separating multiple plates could have been kick-started by plume-induced subduction.
DS202007-1126
2020
Brown, M., Johnson, T., Gardiner, N.J.Plate tectonics and the Archean Earth.Annual Review of Earth and Planetary Sciences, Vol. 48, 1, pp. 291-320.Mantletectonics

Abstract: If we accept that a critical condition for plate tectonics is the creation and maintenance of a global network of narrow boundaries separating multiple plates, then to argue for plate tectonics during the Archean requires more than a local record of subduction. A case is made for plate tectonics back to the early Paleoproterozoic, when a cycle of breakup and collision led to formation of the supercontinent Columbia, and bimodal metamorphism is registered globally. Before this, less preserved crust and survivorship bias become greater concerns, and the geological record may yield only a lower limit on the emergence of plate tectonics. Higher mantle temperature in the Archean precluded or limited stable subduction, requiring a transition to plate tectonics from another tectonic mode. This transition is recorded by changes in geochemical proxies and interpreted based on numerical modeling. Improved understanding of the secular evolution of temperature and water in the mantle is a key target for future research.
DS202005-0724
2020
Brown, M., Kirkland, C.L., Johnson, T.E.Evolution of geodynamics since the Archean: significant change at the dawn of the Phanerozoic.Geology, Vol. 48, 5, pp. 488-492.Globalgeodynamics

Abstract: A time-series analysis of thermobaric ratios (temperature/pressure [T/P]) for Paleoarchean to Cenozoic metamorphic rocks identified significant shifts in mean T/P that may be related to secular change in the geodynamics on Earth. Thermobaric ratios showed significant (>95% confidence) change points at 1910, 902, 540, and 515 Ma, recording drops in mean T/P, and at 1830, 604, and 525 Ma, recording rises in mean T/P. Highest mean T/P occurred during the Mesoproterozoic, and lowest mean T/P occurred from the Cambrian to the Oligocene. Correlated changes were seen between T/P and global data sets of time-constrained hafnium (Hf) and oxygen (O) isotope compositions in zircon. The range of correlated variation in T/P, Hf, and O was larger during the formation of Rodinia than Columbia. Large changes and a wide range for these variables continued through the Phanerozoic, during which a statistically significant 83 m.y. frequency of T/P excursions recorded the high tempo of orogenic activity associated with the separation, migration, and accretion of continental terranes during the formation of Pangea. Since the early Tonian, the decreasing mean T/P of metamorphism, widespread appearance of blueschist and ultrahigh-pressure metamorphism, and wide fluctuations in Hf and O isotope compositions document a change to the modern plate-tectonic regime, characterized by widespread continental subduction and deeper slab breakoff than in the Proterozoic.
DS202002-0169
2019
Buchan, K.L., Ernst, R.E.Giant circumferential dyke swarms: catalogue and characteristics.Dyke Swarms of the World: a modern perspective. Ed. Srivastava Springer, 49p. PdfMantledyke swarms

Abstract: Giant circumferential dyke swarms have a primary geometry that is quasi-circular or quasi-elliptical. Examples and possible examples described previously or identified in this study have outer diameters that range from ~450 to ~2500 km. There has been little study of these features. Here, we present a global catalogue of giant circumferential dyke swarms and discuss their characteristics. All of the identified giant circumferential swarms are of mafic composition. Many, but not all, are associated with a roughly coeval giant radiating dyke swarm whose focus is at or near the centre of the circumferential system. As giant radiating swarms are usually interpreted to focus above mantle plume centres and form a key component of the plumbing system of large igneous provinces (LIPs), it is likely that giant circumferential swarms linked to radiating systems are also plume and LIP related. The largest giant circumferential swarms have diameters comparable to the diameters postulated for the flattened heads of plumes that have risen from the core-mantle boundary, suggesting that they may be associated with the outer edge of a flattening or flattened mantle plume head. Smaller giant circumferential swarms could be linked with small plumes from the mid-mantle or with the edge of a magmatic underplate above a plume head. Giant circumferential dyke swarms on Earth may be analogues of coronae on Venus and similar features on Mars. Coronae are large tectono-magmatic features that typically consist of a quasi-circular or quasi-elliptical graben-fissure system and associated topography (central uplift or depression, and circular rim or moat). In some instances, they are linked to a giant radiating graben-fissure system and LIP-scale volcanism. Both radiating and circumferential graben on Venus and Mars have been interpreted to be underlain by dykes.
DS202012-2209
2020
Buono, G., Fanara, S., Macedonio, G., Palladino, D.M., Petrosino, P., Sottili, G., Pappalardo, L.Dynamics of degassing in evolved alkaline magmas: petrological, experimental and theoretical insights.Earth-Science Reviews, Vol. 211, 103402, 23p. PdfMantlealkaline

Abstract: In the last few decades, advanced monitoring networks have been extended to the main active volcanoes, providing warnings for variations in volcano dynamics. However, one of the main tasks of modern volcanology is the correct interpretation of surface-monitored signals in terms of magma transfer through the Earth's crust. In this frame, it is crucial to investigate decompression-induced magma degassing as it controls magma ascent towards the surface and, in case of eruption, the eruptive style and the atmospheric dispersal of tephra and gases. Understanding the degassing behaviour is particularly intriguing in the case of poorly explored evolved alkaline magmas. In fact, these melts frequently feed hazardous, highly explosive volcanoes (e.g., Campi Flegrei, Somma-Vesuvius, Colli Albani, Tambora, Azores and Canary Islands), despite their low viscosity that usually promotes effusive and/or weakly explosive eruptions. Decompression experiments, together with numerical models, are powerful tools to examine magma degassing behaviour and constrain field observations from natural eruptive products and monitoring signals. These approaches have been recently applied to evolved alkaline melts, yet numerous open questions remain. To cast new light on the degassing dynamics of evolved alkaline magmas, in this study we present new results from decompression experiments, as well as a critical review of previous experimental works. We achieved a comprehensive dataset of key petrological parameters (i.e., 3D textural data for bubbles and microlites using X-ray computed microtomography, glass volatile contents and nanolite occurrence) from experimental samples obtained through high temperature-high pressure isothermal decompression experiments on trachytic alkaline melts at super-liquidus temperature. We explored systematically a range of final pressures (from 200 to 25 MPa), decompression rates (from 0.01 to 1 MPa s?1), and volatile (H2O and CO2) contents. On these grounds, we integrated coherently literature data from decompression experiments on evolved alkaline (trachytic and phonolitic) melts under various conditions, with the aim to fully constrain the degassing mechanisms and timescales in these magmas. Finally, we simulated numerically the experimental conditions to evaluate strengths and weaknesses in decrypting degassing behaviour from field observations. Our results highlight that bubble formation in evolved alkaline melts is primarily controlled by the initial volatile (H2O and CO2) content during magma storage. In these melts, bubble nucleation needs low supersaturation pressures (? 50-112 MPa for homogeneous nucleation, ? 13-25 MPa for heterogeneous nucleation), resulting in high bubble number density (~ 1012-1016 m?3), efficient volatile exsolution and thus in severe rheological changes. Moreover, the bubble number density is amplified in CO2-rich melts (mole fraction XCO2 ? 0.5), in which continuous bubble nucleation predominates on growth. These conditions typically lead to highly explosive eruptions. However, moving towards slower decompression rates (? 10?1 MPa s?1) and H2O-rich melts, permeable outgassing and inertial fragmentation occur, promoting weakly explosive eruptions. Finally, our findings suggest that the exhaustion of CO2 at deep levels, and the consequent transition to a H2O-dominated degassing, can crucially enhance magma vesiculation and ascent. In a hazard perspective, these constraints allow to postulate that time-depth variations of unrest signals could be significantly weaker/shorter (e.g., minor gas emissions and short-term seismicity) during major eruptions than in small-scale events.
DS202003-0333
2020
Burness, S., Smart, K.A., Tappe, S., Stevens, G., Woodland, A.B., Cano, E.Sulphur rich mantle metasomatism of Kaapvaal craton eclogites and its role in redox controlled platinum group element mobility. Xenoliths from Roberts Victor, Jagersfontein, Kimberley ( Kamfersdam), PremierChemical Geology, in press available 57p.Africa, South Africametasomatism

Abstract: Eclogite mantle xenoliths from various kimberlite occurrences on the Kaapvaal craton show evidence for depth- and redox-dependent metasomatic events that led to variable base metal sulphide and incompatible element enrichments. Eclogite xenoliths from the Roberts Victor, Jagersfontein, Kimberley (Kamfersdam) and Premier kimberlites were investigated for their silicate and base metal sulphide geochemistry, stable oxygen isotope compositions and oxybarometry. The variably metasomatised eclogites had basaltic, picritic and gabbroic protolith compositions and have garnet ?18O values that range from +3.3 to +7.9‰, which, when coupled with the trace element characteristics, indicate oceanic lithosphere protoliths that had undergone variable degrees of seawater alteration. The deepest equilibrated eclogites (175220?km depth) from near the base of the Kaapvaal craton lithosphere are the most refractory and feature significant light rare earth element (LREE) depletions. They show the most oxidised redox compositions with ?logƒO2 values of FMQ-3.9 to FMQ-1.5. Subtle metasomatic overprinting of these eclogites resulted in base metal sulphide formation with relatively depleted and highly fractionated HSE compositions. These deepest eclogites and their included base metal sulphides suggest interaction with relatively oxidised melts or fluids, which, based on their HSE characteristics, could be related to precursor kimberlite metasomatism that was widespread within the Kaapvaal craton mantle lithosphere. In contrast, eclogites that reside at shallower, “mid-lithospheric” depths (140180?km) have been enriched in LREE and secondary diopside/phlogopite. Importantly, they host abundant metasomatic base metal sulphides, which have higher HSE contents than those in the deeper eclogites at the lithosphere base. The mid-lithospheric eclogites have more reducing redox compositions (?logfO2?=?FMQ-5.3 ? FMQ-3.3) than the eclogites from the lowermost Kaapvaal lithosphere. The compositional overprint of the shallower mantle eclogites resembles basaltic rather than kimberlitic/carbonatitic metasomatism, which is also supported by their relatively reducing redox state. Base metal sulphides from the mid-lithospheric eclogites have HSE abundances and distributions that are similar to Karoo flood basalts from southern Africa, suggesting a link between the identified shallow mantle metasomatism of the Kaapvaal cratonic lithosphere and the Karoo large igneous event during the Mesozoic. The sulphide-hosted platinum group element abundances of the mid-lithospheric eclogites are higher compared with their analogues from the deeper lithospheric eclogites, which in combination with their contrasting oxidation states, may imply redox-controlled HSE mobility during sulphur-rich metasomatism of continental mantle lithosphere.
DS202008-1372
2020
Burness, S., Smart, K.A., Tappe, S., Stevens, G., Woodland, A.B., Cano, E.Sulphur rich mantle metasomatism of Kaapvaal craton eclogites and its role in redox controlled platinum group element mobility.Chemical Geology, Voll. 542, 119476 23p. pdfAfrica, South Africadeposit - Roberts Victor, Jagersfontein, Kimberley, Kamfersdam, Premier

Abstract: Eclogite mantle xenoliths from various kimberlite occurrences on the Kaapvaal craton show evidence for depth- and redox-dependent metasomatic events that led to variable base metal sulphide and incompatible element enrichments. Eclogite xenoliths from the Roberts Victor, Jagersfontein, Kimberley (Kamfersdam) and Premier kimberlites were investigated for their silicate and base metal sulphide geochemistry, stable oxygen isotope compositions and oxybarometry. The variably metasomatised eclogites had basaltic, picritic and gabbroic protolith compositions and have garnet ?18O values that range from +3.3 to +7.9‰, which, when coupled with the trace element characteristics, indicate oceanic lithosphere protoliths that had undergone variable degrees of seawater alteration. The deepest equilibrated eclogites (175-220 km depth) from near the base of the Kaapvaal craton lithosphere are the most refractory and feature significant light rare earth element (LREE) depletions. They show the most oxidised redox compositions with ?logƒO2 values of FMQ-3.9 to FMQ-1.5. Subtle metasomatic overprinting of these eclogites resulted in base metal sulphide formation with relatively depleted and highly fractionated HSE compositions. These deepest eclogites and their included base metal sulphides suggest interaction with relatively oxidised melts or fluids, which, based on their HSE characteristics, could be related to precursor kimberlite metasomatism that was widespread within the Kaapvaal craton mantle lithosphere. In contrast, eclogites that reside at shallower, “mid-lithospheric” depths (140-180 km) have been enriched in LREE and secondary diopside/phlogopite. Importantly, they host abundant metasomatic base metal sulphides, which have higher HSE contents than those in the deeper eclogites at the lithosphere base. The mid-lithospheric eclogites have more reducing redox compositions (?logfO2 = FMQ-5.3 ? FMQ-3.3) than the eclogites from the lowermost Kaapvaal lithosphere. The compositional overprint of the shallower mantle eclogites resembles basaltic rather than kimberlitic/carbonatitic metasomatism, which is also supported by their relatively reducing redox state. Base metal sulphides from the mid-lithospheric eclogites have HSE abundances and distributions that are similar to Karoo flood basalts from southern Africa, suggesting a link between the identified shallow mantle metasomatism of the Kaapvaal cratonic lithosphere and the Karoo large igneous event during the Mesozoic. The sulphide-hosted platinum group element abundances of the mid-lithospheric eclogites are higher compared with their analogues from the deeper lithospheric eclogites, which in combination with their contrasting oxidation states, may imply redox-controlled HSE mobility during sulphur-rich metasomatism of continental mantle lithosphere.
DS202008-1373
2020
Buyse, F., Dewaele, S., Decree, S., Mees, F.Mineralogical and geochemical study of the rare earth element mineralization at Gakara ( Burundi).Ore Geology Reviews, Vol. 124, 103659 10p. PdfAfrica, BurundiREE

Abstract: The rare earth element (REE) mineralization of Gakara (Burundi) has first been discovered in 1936 and has periodically been the subject of geological studies, at times when the exploitation of bastnäsite-(Ce) and monazite-(Ce) was economically interesting. This study focuses on the establishment of a mineral paragenesis for Gakara, with special attention to the REE-bearing phases, to understand the formation history of the deposit. The paragenesis can be subdivided into 3 stages: primary ore deposition, brecciation stage and supergene alteration. Evidence for fenitization processes (i.e. pinkish-red cathodoluminescence of K-feldpar, brecciation stage) and the strong enrichment of light REEs in bastnäsite and monazite substantiate the hypothesis of a structurally controlled hydrothermal mineralization with a strong carbonatitic affinity. This likely confirms the association of the Gakara REE deposit with the Neoproterozoic alignment of alkaline complexes and carbonatites along the present-day Western Rift. It suggests a direct link with a - currently unidentified - carbonatitic body at depth, possibly derived from a predominantly metasomatized lithospheric mantle.
DS202011-2032
2020
Cai, W-C., Zhang, Z-C., Zhu, J., Santosh, M., Pan, R-H.Genesis of high ni-olivine phenocrysts of the Dali picrites in the central Emeishan large igneous province.Geological Magazine, doi: 10.1017/ S0016756820001053 10p. Chinapicrites

Abstract: The Emeishan large igneous province (ELIP) in SW China is considered to be a typical mantle-plume-derived LIP. The picrites formed at relatively high temperatures in the ELIP, providing one of the important lines of argument for the role of mantle plume. Here we report trace-element data on olivine phenocrysts in the Dali picrites from the ELIP. The olivines are Ni-rich, and characterized by high (>1.4) 100×Mn/Fe value and low (<13) 10 000×Zn/Fe value, indicating a peridotite-dominated source. Since the olivine-melt Ni partition coefficient (KDNiol/melt) will decrease at high temperatures and pressures, the picrites derived from peridotite melting at high pressure, and that crystallized olivines at lower pressure, can generate high concentrations of Ni in olivine phenocrysts, excluding the necessity of a metasomatic pyroxenite contribution. Based on the Al-in-olivine thermometer, olivine crystallization temperature and mantle potential temperature (T P) were calculated at c. 1491°C and c. 1559°C, respectively. Our results are c. 200°C higher than that of the normal asthenospheric mantle, and are consistent with the role of a mantle thermal plume for the ELIP.
DS202008-1374
2020
Campbell, D., Zurevinski, S., Elliott, B.Geochemistry and glacial dispersal patterns of kimberlitic indicator minerals in the South Slave Province, NT.Goldschmidt 2020, 1p. AbstractCanada, Northwest Territoriesgarnets

Abstract: The geochemistry and distribution of garnets in the southern Slave Province could have considerable implications for drift prospecting and diamond potential. Presented here is a study interpretting geochemistry in dispersal trains of the Slave Province. Over one-hundred-thousand garnets have been sampled from the northern Slave Province with quantitative analyses conducted on each sample, and the data has been compiled for public release (NTGS Data Hub, 2018). A smaller subset of samples have been collected in the southern Slave Province by this study and the NTGS within recent years. Data from the NTGS is used in this study to construct regional maps showing dispersal trains of indicator minerals and chemistry of indicator garnets throughout the region. The variation in dispersal train pattern, size, mineralogy, and chemistry are being utilized to assess the southern Slave for it’s kimberlite potential. The geochemistry of garnets is used to make further observations into the diamond potential of the area using the garnet classifications G3D, G4D, G5D, and G10D (Grutter et al., 2004). It has been observed that there is an abundance of Na2O rich (>0.07 wt %) garnets in the northern Slave Province and a deficit of Na2O (<0.07 wt %) in garnets of the south. There is also a visible discrepency in olivine in the north and south, with the north Slave showing olivine in dispersal trains and the south lacking any olivine. These discrepancies in Na2O could be indicative of pressure/temperature conditions that coincide with diamond formation in the north (Grutter et al., 2004). The olivine dispersal may be the product of glacial dispersal in conjunction with the facies/mineralogy of kimberlites in the immediate area.
DS202008-1375
2019
Campbell, J.A.H.Financing diamond projects.The Journal of the Southern African Insitute of Mining and Metallurgy, Vol. 119, Feb. 6p. PdfGlobalfinancing

Abstract: Investment in diamond exploration has been declining over the past decade, in spite of positive long-term industry fundamentals and a growing interest in diamonds as an investment category. The lack of new significant discoveries in recent years has eroded investor confidence, yet no new discoveries are possible without investment in exploration. Junior ‘mine finders’ have been the hardest hit. Their agility, tenacity, and appetite for risk are not sufficient to attract the funding required, even at the greenfield stage. Developing new discoveries into mineral resources can be crippling without solid financial support. Junior incubators could play a crucial role, especially at the project evaluation stage - but where are they? Alternatives to traditional funding mechanisms have become available, many still untested in the junior diamond exploration space. Valuable lessons can be drawn from the past and used to inform emerging new strategies.
DS202008-1376
2018
Campbell, J.A.H., Jooste, V.The AK6 kimberlite - discovery through to production: learning the lessons of history.Botswana Journal of Earth Sciences, Vol. 7, pp. 13-28. pdfAfrica, Botswanadeposit - AK6

Abstract: The AK6 kimberlite in north-eastern Botswana, better known as Karowe, is today one of the world?s top diamond producers by value. Its potential, however, was not recognised when AK6 was first discovered some fifty years ago. This paper traces the history of Karowe from the discovery of AK6 through to evaluation and production, reflecting on the interplay of economic, technical and corporate elements and highlighting some of the lessons learnt along this journey. Karowe Mine has been operating since 2012 and is fully owned by Lucara Diamond Corporation. In 2015, Karowe yielded the second largest diamond ever found, the 1,109ct Lesedi La Rona (Fig. 1).
DS202009-1615
2020
Cannao, E., Scambelluri, M., Bebout, G.E., Agostini, S., Pettke, T., Godard, M., Crispini, L.Ophicarbonate evolution from seafloor to subduction and implications for deep-Earth C cycling.Chemical Geology, Vol. 546, 119626 29p. PdfMantlecarbon, subduction

Abstract: The chemical and physical processes operating during subduction-zone metamorphism can profoundly influence the cycling of elements on Earth. Deep-Earth carbon (C) cycling and mobility in subduction zones has been of particular recent interest to the scientific community. Here, we present textural and geochemical data (CO, Sr isotopes and bulk and in-situ trace element concentrations) for a suite of ophicarbonate rocks (carbonate-bearing serpentinites) metamorphosed over a range of peak pressure-temperature (P-T) conditions together representing a prograde subduction zone P-T path. These rocks, in order of increasing peak P-T conditions, are the Internal Liguride ophicarbonates (from the Bracco unit, N. Apennines), pumpellyite- and blueschist-facies ophicarbonates from the Sestri-Voltaggio zone (W. Ligurian Alps) and the Queyras (W. Alps), respectively, and eclogite-facies ophicarbonates from the Voltri Massif. The Bracco oceanic ophicarbonates retain breccia-like textures associated with their seafloor hydrothermal and sedimentary origins. Their trace element concentrations and ?18OVSMOW (+15.6 to +18.2‰), ?13CVPDB (+1.1 to +2.5‰) and their 87Sr/86Sr (0.7058 to 0.7068), appear to reflect equilibration during Jurassic seawater-rock interactions. Intense shear deformation characterizes the more deeply subducted ophicarbonates, in which prominent calcite recrystallization and carbonation of serpentinite clasts occurred. The isotopic compositions of the pumpellyite-facies ophicarbonates overlap those of their oceanic equivalents whereas the most deformed blueschist-facies sample shows enrichments in radiogenic Sr (87Sr/86Sr?=?0.7075) and depletion in 13C (with ?13C as low as ?2.0‰). These differing textural and geochemical features for the two suites reflect interaction with fluids in closed and open systems, respectively. The higher-P-metamorphosed ophicarbonates show strong shear textures, with coexisting antigorite and dolomite, carbonate veins crosscutting prograde antigorite foliation and, in some cases, relics of magnesite-nodules enclosed in the foliation. These rocks are characterized by lower ?18O (+10.3 to 13.0‰), enrichment in radiogenic Sr (87Sr/86Sr up to 0.7096) and enrichment in incompatible and fluid-mobile element (FME; e.g., As, Sb, Pb). These data seemingly reflect interaction with externally-derived metamorphic fluids and the infiltrating fluids likely were derived from dehydrating serpentinites with hybrid serpentinite-sediment compositions. The interaction between these two lithologies could have occurred prior to or after dehydration of the serpentinites elsewhere. We suggest that decarbonation and dissolution/precipitation processes operating in ancient subduction zones, and resulting in the mobilization of C, are best traced by a combination of detailed field and petrographic observations, C, O and Sr isotope systematics (i.e., 3D isotopes), and FME inventories. Demonstration of such processes is key to advancing our understanding of the influence of subduction zone metamorphism on the mobilization of C in subducting reservoirs and the efficiency of delivery of this C to depths beneath volcanic arcs and into the deeper mantle.
DS202007-1127
2020
Cannao, E., Tiepolo, M., Bebout, G.E., Scambelluri, M.Into the deep and beyond: carbon and nitrogen subduction recycling in secondary peridotites. Gagnone metaperidotitesEarth and Planetary Science Letters, Vol. 543, 116328 14p. PdfEurope, Switzerland, Alpsboron diamonds

Abstract: Understanding the volatile cycles at convergent margins is fundamental to unravel the Earth's evolution from primordial time to present. The assessment of fluid-mobile and incompatible element uptake in serpentinites via interaction with seawater and subduction-zone fluids is central to evaluate the global cycling of the above elements in the Earth's mantle. Here, we focus on the carbon (C), nitrogen (N) and C isotope compositions of chlorite harzburgites and garnet peridotites deriving from subduction-zone dehydration of former oceanic dehydration of serpentinite - i.e., metaperidotites (Cima di Gagnone, Swiss Central Alps) with the aim of evaluating the contribution of these rocks to the global C-N cycling. These ultramafic rocks, enclosed as lenses in a metasedimentary mélange, represent the destabilization of antigorite and chlorite at high-pressure/temperature (P/T) along a slab-mantle interface. Chlorite- and garnet-bearing rocks have similar ranges in C concentration ([C] = 210 - 2465 ppm and 304 - 659 ppm, respectively), with one magnesite-bearing chlorite harzburgite hosting 11000 ppm C. The average N concentrations ([N]) of the garnet peridotites (54 ± 15 ppm, one standard deviation indicated) are higher than those of the chlorite harzburgites (29 ± 6 ppm). The C of total C (TC) and total organic C (TOC) values of the Gagnone metaperidotites range from -12.2 to -17.8‰ and from -27.8 to -26.8‰, respectively, excluding the magnesite-bearing chlorite harzburgites with higher values of -7.2‰ (TC) and -21.2‰ (TOC). The [C] of these rocks are comparable to those of serpentinites form modern and ancient oceanic environments and with [C] of high-P serpentinites. However, the lack of preserved serpentinite precursors makes it difficult to determine whether release of H2O during high-P breakdown of antigorite and chlorite is coupled with significant C release to fluids. The C values appear to reflect mixing between seawater-derived carbonate and a reduced C source and a contribution from the host metasedimentary rocks ([C] = 301 ppm; [N] = 33 ppm; TC C = -24.4‰; TOC C = -27.0‰) cannot be completely excluded. The C-O isotope composition of the carbonate in magnesite-bearing chlorite harzburgites is compatible with progressive devolatilization at oxidized conditions, whereas the signatures of the majority of the other Gagnone samples appear to reflect different degree of interaction with sedimentary fluids. The [N] of the Gagnone metaperidotites are higher than those of oceanic and subducted serpentinites and show a range similar to that of high-P antigorite-serpentinites from mantle wedges. This enrichment is compatible with fluid-mediated chemical exchange with the surrounding metasedimentary rocks leading to strong modification of the Gagnone metaperidotites' geochemistry during prograde subduction along the slab-mantle interface. Comparing the C data reported in this study with published C values for diamonds, we suggest that the volatile recycling via Gagnone-like metaperidotites in subduction zones could contribute to deep-Earth diamond genesis and in particular to the formation of blue boron (B)-bearing diamonds. Our results highlight that the subduction of secondary peridotites evolved along the slab-mantle interface is a viable mechanism to inject volatiles into the deep mantle, particularly in hotter geothermal regimes such as the ones active during the early Earth's history.
DS202010-1831
2020
Cao, Y., Jung, H., Ma, J.Seismic properties of a unique olivine-rich eclogite in the western Gneiss region, Norway.Minerals ( MDPI), 10.339/min10090774 22p. PdfEurope, Norwayeclogites

Abstract: Investigating the seismic properties of natural eclogite is crucial for identifying the composition, density, and mechanical structure of the Earth’s deep crust and mantle. For this purpose, numerous studies have addressed the seismic properties of various types of eclogite, except for a rare eclogite type that contains abundant olivine and orthopyroxene. In this contribution, we calculated the ambient-condition seismic velocities and seismic anisotropies of this eclogite type using an olivine-rich eclogite from northwestern Flemsøya in the Nordøyane ultrahigh-pressure (UHP) domain of the Western Gneiss Region in Norway. Detailed analyses of the seismic properties data suggest that patterns of seismic anisotropy of the Flem eclogite were largely controlled by the strength of the crystal-preferred orientation (CPO) and characterized by significant destructive effects of the CPO interactions, which together, resulted in very weak bulk rock seismic anisotropies (AVp = 1.0-2.5%, max. AVs = 0.6-2.0%). The magnitudes of the seismic anisotropies of the Flem eclogite were similar to those of dry eclogite but much lower than those of gabbro, peridotite, hydrous-phase-bearing eclogite, and blueschist. Furthermore, we found that amphibole CPOs were the main contributors to the higher seismic anisotropies in some amphibole-rich samples. The average seismic velocities of Flem eclogite were greatly affected by the relative volume proportions of omphacite and amphibole. The Vp (8.00-8.33 km/s) and Vs (4.55-4.72 km/s) were remarkably larger than the hydrous-phase-bearing eclogite, blueschist, and gabbro, but lower than dry eclogite and peridotite. The Vp/Vs ratio was almost constant (avg. ? 1.765) among Flem eclogite, slightly larger than olivine-free dry eclogite, but similar to peridotite, indicating that an abundance of olivine is the source of their high Vp/Vs ratios. The Vp/Vs ratios of Flem eclogite were also higher than other (non-)retrograded eclogite and significantly lower than those of gabbro. The seismic features derived from the Flem eclogite can thus be used to distinguish olivine-rich eclogite from other common rock types (especially gabbro) in the deep continental crust or subduction channel when high-resolution seismic wave data are available.
DS202003-0334
2019
Carlson, R.W., Garcon, M., O'Neil, J., Reimink, J.,Rizo, H.The nature of the Earth's crust.Chemical Geology, Vol. 530, 25p. Available pdfMantleArchean geology

Abstract: Recycling of crust into the mantle has left only small remnants at Earth’s surface of crust produced within a billion years of Earth formation. Few, if any, of these ancient crustal rocks represent the first crust that existed on Earth. Understanding the nature of the source materials of these ancient rocks and the mechanism of their formation has been the target of decades of geological and geochemical study. This traditional approach has been expanded recently through the ability to simultaneously obtain U-Pb age and initial Hf isotope data for zircons from many of these ancient, generally polymetamorphic, rocks. The addition of information from the short-lived radiometric systems 146Sm-142Nd and 182Hf-182W allows resolution of some of the ambiguities that have clouded the conclusions derived from the long-lived systems. The most apparent of these is clear documentation that Earth experienced major chemical differentiation events within the first tens to hundreds of millions of years of its formation, and that Earth’s most ancient crustal rocks were derived from these differentiated sources, not from primitive undifferentiated mantle. Eoarchean rocks from the North Atlantic Craton and the Anshan Complex of the North China Craton have sources in an incompatible-element-depleted mantle that dates to 4.44.5 Ga. Hadean/Eoarchean rocks from two localities in Canada show the importance of remelting of Hadean mafic crust to produce Eoarchean felsic crust. The mafic supracrustal rocks of the Nuvvuagittuq Greenstone Belt are a possible example of the Hadean mafic basement that is often called upon to serve as the source for the high-silica rocks that define continental crust. Many, but not all, ancient terranes show a shift in the nature of the sources for crustal rocks, and possibly the physical mechanism of crust production, between 3.03.6 Ga. This transition may reflect the initiation of modern plate tectonics. Eoarchean/Hadean rocks from some terranes, however, also display compositional characteristics expected for convergent margin volcanism suggesting that at least some convergent margin related magmatism began in the Hadean. The persistence of isotopic variability in 142Nd/144Nd into the mid-Archean, and the eventual reduction in that variability by the end of the Archean, provides new information on the efficiency by which mantle convection recombined the products of Hadean silicate-Earth differentiation. The rate of crust production and recycling in the Hadean/Archean, however, is not resolved by these data beyond the observation that extreme isotopic compositions, such as expected for Hadean evolved, continent-like, crust are not observed in the preserved Eoarchean rock record. The lack of correlation between 142Nd/144Nd and 182W/184W variation in Archean rocks suggests that these two systems track different processes; the Sm-Nd system mantle-crust differentiation while Hf-W is dominated by core formation. The major silicate differentiation controlling Sm/Nd fractionation occurred at ?4.4 Ga, possibly as a result of the Moon-forming impact, after the extinction of 182Hf.
DS202011-2033
2020
Casola, V., France, L., Galy, A., Bouden, N., Villeneuve, J.No evidence for carbon enrichment in the mantle source of carbonatites in eastern Africa.Geology, Vol. 48, 10, pp. 971976. pdfAfrica, Tanzaniadeposit - Oldoinyo Lengai

Abstract: Carbonatites are unusual, carbon-rich magmas thought to form either by the melting of a carbon-rich mantle source or by low-degree partial melting of a carbon-poor (<80 ppm C) mantle followed by protracted differentiation and/or immiscibility. Carbonate-bearing mantle xenoliths from Oldoinyo Lengai (East African Rift), the only active volcano erupting carbonatites, have provided key support for a C-rich mantle source. Here, we report unique microscale O and C isotopic analyses of those carbonates, which are present as interstitial grains in the silicate host lava, veins in the xenoliths, and pseudo-inclusions in olivine xenoliths. The ?18O values vary little, from 19‰ to 29‰, whereas ?13C values are more variable, ranging from -23‰ to +0.5‰. We show that such carbonate ?18O values result from the low-temperature precipitation of carbonate in equilibrium with meteoric water, rather than under mantle conditions. In this framework, the observed ?13C values can be reproduced by Rayleigh distillation driven by carbonate precipitation and associated degassing. Together with petrological evidence of a physical connection between the three types of carbonates, our isotopic data support the pedogenic formation of carbonates in the studied xenoliths by soil-water percolation and protracted crystallization along xenolith cracks. Our results refute a mechanism of C enrichment in the form of mantle carbonates in the mantle beneath the Natron Lake magmatic province and instead support carbonatite formation by low-degree partial melting of a C-poor mantle and subsequent protracted differentiation of alkaline magmas.
DS202012-2210
2020
Casola, V., France, L., Galy, A., Bouden, N., Villeneuve, J.No evidence for carbon enrichment in the mantle source of carbonatites in eastern Africa.Geology, Vol. 48, 10, 5p. PdfAfrica, Tanzaniacarbonatites

Abstract: Carbonatites are unusual, carbon-rich magmas thought to form either by the melting of a carbon-rich mantle source or by low-degree partial melting of a carbon-poor (<80 ppm C) mantle followed by protracted differentiation and/or immiscibility. Carbonate-bearing mantle xenoliths from Oldoinyo Lengai (East African Rift), the only active volcano erupting carbonatites, have provided key support for a C-rich mantle source. Here, we report unique microscale O and C isotopic analyses of those carbonates, which are present as interstitial grains in the silicate host lava, veins in the xenoliths, and pseudo-inclusions in olivine xenoliths. The ?18O values vary little, from 19‰ to 29, whereas ?13C values are more variable, ranging from -23‰ to +0.5‰. We show that such carbonate ?18O values result from the low-temperature precipitation of carbonate in equilibrium with meteoric water, rather than under mantle conditions. In this framework, the observed ?13C values can be reproduced by Rayleigh distillation driven by carbonate precipitation and associated degassing. Together with petrological evidence of a physical connection between the three types of carbonates, our isotopic data support the pedogenic formation of carbonates in the studied xenoliths by soil-water percolation and protracted crystallization along xenolith cracks. Our results refute a mechanism of C enrichment in the form of mantle carbonates in the mantle beneath the Natron Lake magmatic province and instead support carbonatite formation by low-degree partial melting of a C-poor mantle and subsequent protracted differentiation of alkaline magmas.
DS202011-2034
2016
Castillo Clerici, A.M., Gomes, C.B., De Min, A., Comin-Chiaramonti, P.Heavy minerals in the sediments from Paraguay rivers as indicators for diamonds occurrences. *** NOTE DATEBol. Mus. Nac. Hist. Parag. *** ENG, Vol. 20, 2, pp. 188-204. pdfSouth America, Paraguaygeochemistry

Abstract: After some works of Jaime Baez-Presse that quoted the presence of diamonds in Eastern Paraguay, we have perfprmed a whole sampling a study relative to the indicator mineral for diamonds. Indicator minerals are mineral species that, when appearing as transported grains in clastic sediments, indicate the presence in bedrock of a specific type of mineralization, hydrothermal alteration or lithology. Their physical and chemical characteristics, including a relatively high density (heavy minerals), facilitate their preservation and identification. The heavy minerals represent an important exploration method for detecting a variety of ore deposit types including diamond, gold, Ni-Cu, PGE, and so on.. One of the most significant events in the application of indicator mineral methods in the past was the diamond exploration. This paper provides an overview of indicator mineral methods, i.e. presence of Cr-diopside, Pyrope-rich garnet and Picroilmenite, for diamond exploration along the Eastern Paraguay river. Unfortunately the above heavy mineraks, generally associated to the diamonds, do not appear in Eastern Paraguay, excluding this Country as a potential source for the diamond as economic potential source.
DS202005-0725
2020
Castillo-Oliver, M., Giuliani, A., Griffin, W.L., Drsydale, Rn.New constraints on the source, composition, and post-emplacement modification of kimberlites from in situ C-O-Sr-isotope analyses of carbonates from the Benfontein sills ( South Africa).Contributions to Mineralogy and Petrology, in press available, 21p. PdfAfrica, South Africadeposit - Benfontein

Abstract: Primary carbonates in kimberlites are the main CO2 carriers in kimberlites and thus can be used to constrain the original carbon and oxygen-isotope composition of kimberlite melts and their deep mantle sources. However, the contribution of syn- and post-emplacement processes to the modification of the C-O-isotope composition of kimberlites is yet to be fully constrained. This study aims to shed new light on this topic through a detailed textural, compositional (major and trace elements), and in situ C-O-Sr isotopic characterisation of carbonates in the Benfontein kimberlite sills (Kimberley, South Africa). Our multi-technique approach not only reveals the petrographic and geochemical complexity of carbonates in kimberlites in unprecedented detail, but also allows identification of the processes that led to their formation, including: (1) magmatic crystallisation of Sr-rich calcite laths and groundmass; (2) crystallisation of late groundmass calcite from hydrothermal fluids; and (3) variable degrees of crustal contamination in carbonate-rich diapirs and secondary veins. These diapirs most likely resulted from a residual C-O-H fluid or carbonate melt with contributions from methane-rich fluids from the Dwyka shale wall rock, leading to higher 87Sr/86Sr and ?18O, but lower ?13C values than in pristine magmatic calcite. Before coalescing into the diapiric segregations, these fluids/melts also variably entrained early formed calcite laths and groundmass phases. Comparison between in situ and bulk-carbonate analyses confirms that O isotopic analyses of bulk carbonates from kimberlite rocks are not representative of the original isotopic signature of the kimberlite magma, whereas bulk C-isotope compositions are similar to those of the pristine magmatic carbonates. Calcite laths and most groundmass grains at Benfontein preserve isotopic values (?18O?=?6-8‰ and ?13C?=???4 to ??6‰), similar to those of unaltered carbonatites worldwide, which, therefore, probably correspond to those of their parental melts. This narrow range suggests kimberlite derivation from a mantle source with little contribution from recycled crustal material unless the recycled material had isotopic composition indistinguishable from typical mantle values.
DS202009-1616
2020
Cawood, P.Earth Matters: a temp to our planet's evolution.Geology, Vol. 48, 5, pp. 525-526.Mantlelithosphere

Abstract: Earth is our home and we, along with all life, are dependent on it for our future. There is no more fundamental issue, from either a philosophical or a practical viewpoint, than to understand Earth history and how it has evolved to form the environment we live in and the resources on which we depend. The origin of Earth, and our role within it, has fascinated humanity from time immemorial, yet we know remarkably little of Earth’s long-term temporal and spatial evolution. Apart from the last few thousand years, most of our 4.55 billion years of history is preserved in the rock archive, but that record is incomplete, and our knowledge of it decreases with increasing age and depth. Furthermore, the long-term record is restricted to relatively buoyant continental lithosphere (crust and upper mantle). Thus, continents provide the only long-term record of development and evolution of our planet’s atmosphere, oceans, crust and underlying mantle from the time of their formation to the present day. Over the past quarter century, our ability to interrogate the continental record has dramatically improved through developments in microanalysis and in computing. This has enabled ever-increasing documentation of spatial and temporal variations in rock units and events, including the composition and pressure-temperature-time conditions to which specific rocks and regions were subjected, and from this data an increased ability to develop high-fidelity numerical models of the processes involved. These expanding data sets and models highlight the dynamic nature of our planet’s feedbacks between its solid and surficial reservoirs, and their response to evolving internal and external forces.
DS202004-0502
2020
Cawood, P.A., Wang, W., Zhao, T., Xu, Y., Mulder, J.A., Pisarevsky, S.A., Zhang, L., Gan, C., He, H., Liu, H., Qi, L., Wang, Y., Yao, J., Zhao, G., Zhou, M-F., Zi, J-W.Deconstructing south China and consequences for reconstructing Nuna and Rodinia.Earth-Science Reviews, in press available, 70p. PdfChinatectonics

Abstract: Contrasting models for internal and external locations of South China within the Nuna and Rodinia supercontinents can be resolved when the current lithotectonic associations of Mesoproterozoic and older rocks units that constitute the craton are redefined into four lithotectonic domains: Kongling, Kunming-Hainan, Wuyi, and Coastal. The Kongling and Kunming-Hainan domains are characterized by isolated Archean to early Paleoproterozoic rock units and events and crop out in northern and southern South China, respectively. The Kunming-Hainan Domain is preserved in three spatially separated regions at Kunming (southwestern South China), along the Ailaoshan shear zone, and within Hainan Island. Both domains were affected by late Paleoproterozoic tectonothermal events, indicating their likely juxtaposition by this time to form the proto-Yangtze Block. Late Paleoproterozoic and Mesoproterozoic sedimentary and igneous rock units developed on the proto-Yangtze Block, especially in its southern portions, and help link the rock units that formed along the shear zone at Ailaoshan and on Hainan Island into a single, spatially unified unit prior to Paleozoic to Cenozoic structural disaggregation and translation. The Wuyi Domain consists of late Paleoproterozoic rock units within a NE-SW trending, fault-bounded block in eastern South China. The Coastal Domain lies east of the Wuyi domain and is inferred to constitute a structurally separate block. Basement to the domain is not exposed, but zircon Hf model ages from Mesozoic granites suggest Mesoproterozoic basement at depth. The Archean to Paleoproterozoic tectonothermal record of the Kongling and Kunming-Hainan domains corresponds closely with that of NW Laurentia, suggesting all were linked, probably in association with assembly and subsequent partial fragmentation of the Nuna supercontinent. Furthermore, the age and character of Mesoproterozoic magmatism and detrital zircon signature of sedimentary rocks in the proto-Yangtze Block matches well with western Laurentia and eastern Australia-Antarctica. In particular, the detrital zircon signature of late Paleoproterozoic to early Mesoproterozoic sedimentary units in the block (e.g. Dongchuan Group) share a similar age spectrum with the Wernecke Supergroup of northwest Laurentia. This, together with similarities in the type and age of Fe-Cu mineralization in the domain with that in eastern Australia-Antarctica, especially northeast Australia, suggests a location adjacent to northwest Laurentia, southern Siberia, and northeast Australia within the Nuna supercontinent. The timing and character of late Paleoproterozoic magmatic activity in the Wuyi domain along with age of detrital zircons in associated sedimentary rocks matches the record of northern India. During rifting between Australia-Antarctica and Laurentia in the late Mesoproterozoic, the proto-Yangtze Block remained linked to northeast Australia. During accretionary orogenesis in the early Neoproterozoic, the proto-Yangtze Block assembled with the Wuyi Domain along the northern margin of India. The Coastal domain likely accreted at this time forming the South China Craton. Displacement of the Hainan and Ailaoshan assemblages from southwest of the Kunming assemblage likely occurred in the Cenozoic with the activation of the Ailaoshan-Red River fault system but could have begun in the early to mid-Paleozoic based on evidence for tectonothermal events in the Hainan assemblage.
DS202001-0004
2019
Cecchi, V.M., Rossi, M., Ghiara, M.R., Franza, A.An unrevealed treasure: a new Italian meteorite from the Royal Mineralogical Museum of Naples.Geology Today, Vol. 35, 6, pp. 212-216.Europe, Italymeteorite

Abstract: Naturalistic and geo?mineralogical museum collections are one of the most relevant sources for research on meteorites the world over. Here, we present the description of a new Italian meteorite that has been recently discovered at the Royal Mineralogical Museum of Naples in Italy.
DS202009-1617
2006
Chalapathi Rao, N.V.Mesoproterozoic diamondiferous ultramafic pipes at Majhgawan and Hinota, Panna area, central India: key to the nature of sub-continental lithospheric mantle beneath the Vindhyan basin.Journal of Earth System Science *** note date 2006 , Vol. 115, 1, Feb. pp. 161-183. pdfIndiadeposit - Panna

Abstract: Amongst all the perceptible igneous manifestations (volcanic tuffs and agglomerates, minor rhyolitic flows and andesites, dolerite dykes and sills near the basin margins, etc.) in the Vindhyan basin, the two Mesoproterozoic diamondiferous ultramafic pipes intruding the Kaimur Group of sediments at Majhgawan and Hinota in the Panna area are not only the most conspicuous but also well-known and have relatively deeper mantle origin. Hence, these pipes constitute the only yet available ‘direct’ mantle samples from this region and their petrology, geochemistry and isotope systematics are of profound significance in understanding the nature of the sub-continental lithospheric mantle beneath the Vindhyan basin. Their emplacement age (? 1100 Ma) also constitutes the only reliable minimum age constrain on the Lower Vindhyan Group of rocks. The Majhgawan and Hinota pipes share the petrological, geochemical and isotope characteristics of kimberlite, orangeite (Group II kimberlite) and lamproite and hence are recognised as belonging to a ‘transitional kimberlite-orangeite-lamproite’ rock type. The namemajhagwanite has been proposed by this author to distinguish them from other primary diamond source rocks. The parent magma of the Majhgawan and Hinota pipes is envisaged to have been derived by very small (<1%) degrees of partial melting of a phlogopite-garnet lherzolite source (rich in titanium and barium) that has been previously subjected to an episode of initial depletion (extensive melting during continent formation) and subsequent metasomatism (enrichment). There is absence of any subduction-related characteristics, such as large negative anomalies at Ta and Nb, and therefore, the source enrichment (metasomatism) of both these pipes is attributed to the volatile- and K-rich, extremely low-viscosity melts that leak continuously to semi-continuously from the asthenosphere and accumulate in the overlying lithosphere. Lithospheric/crustal extension, rather than decompression melting induced by a mantle plume, is favoured as the cause of melting of the source regions of Majhgawan and Hinota pipes. This paper is a review of the critical evaluation of the published work on these pipes based on contemporary knowledge derived from similar occurrences elsewhere.
DS202008-1377
2020
Chalapathi Rao, N.V., Giri, R.K., Pandey, A.Kimberlites, lamproites and lamprophyres from the Indian shield: highlights of researches during 2016-2019.Proceedings Natural Science Academy, Vol. 86, 1, pp. 301-311.Indiakimberlite, lamproites

Abstract: Highlights of researches on kimberlites, lamproites and lamprophyres (and their entrained xenoliths) during 2016-2019 from the Indian context are presented. A few previously unknown occurrences have been brought to light, and a wealth of petrological, geochemical and isotopic data on these rocks became available. All these studies provided new insights into the nomenclatural as well as geodynamic aspects such as subduction-tectonics, mantle metasomatism, lithospheric thickness, supercontinent amalgamation, and break-up and nature of the sub-continental lithospheric mantle from the Indian shield.
DS202009-1618
2020
Chalapathi Rao, N.V., Giri, R.K., Sharma, A., Pandey, A.Lamprophyres from the Indian shield: a review of their occurrence, petrology, tectonomagmatic significance and relationship with the kimberlites and related rocks.Episodes, Vol. 43, 1, pp. 231-248.Indialamprophyres

Abstract: Lamprophyres are some of the oldest recognized alkaline rocks and have been studied for almost the last 150 years. Known for hosting economic minerals such as gold, diamond and base metals, they are also significant in our understanding of the deep-mantle processes (viz., mantle metasomatism and mantleplume-lithosphere interactions) as well as large-scale geodynamic processes (viz., subduction-tectonics, supercontinent amalgamation and break-up). The Indian shield is a collage of distinct cratonic blocks margined by the mobile belts and manifested by large igneous provinces (LIPs) such as the Deccan. A plethora of lamprophyres, varying in age from the Archaean to the Eocene, with diverse mineralogical and geochemical compositions, are recorded from the Indian shield and played a key role in clarifying the tectonic processes, especially during the Paleo- and Mesoproterozoic and the Late Cretaceous. A comprehensive review of the occurrence, petrology, geochemistry and origin of the Indian lamprophyres is provided here highlighting their tectonomagmatic significance. The relationship of the lamprophyres to the Kimberlite clan rocks (KCRs), focusing on the Indian examples, is also critically examined.
DS202007-1128
2020
Chanturia, V.A., Dvoichenkova, G.P., Morozov, V.V., Kovalchuk, O.E., Pdkamennyi, Yu.A., Yakovlev, V.N.Selective attachment of luminophore bearing emulsion at diamonds - mechanism analysis and mode selection. X-rayJournal of Mining Science, Vol. 56, 1, pp. 96-103. pdfGloballuminescence

Abstract: The authors present an efficient modification method of X-ray fluorescence separation with mineral and organic luminophores used to adjust spectral and kinetic characteristics of anomalously luminescent diamonds. The mechanism of attachment of luminophores at diamonds and hydrophobic minerals is proved, including interaction between the organic component of emulsions and the hydrophobic surface of a treated object and the concentration of insoluble luminophore grains at the organic and water interface. Selective attachment of the luminophore-bearing organic phase of emulsion at the diamond surface is achieved owing to phosphatic dispersing agents. Tri-sodium phosphate and sodium hexametaphosphate added to emulsion reduce attachment of the luminophore-bearing organic phase at the surface of kimberlite minerals. It is shown that phosphate concentration of 1.0-1.5 g/l modifies and stabilizes spectral and kinematic parameters of kimberlite mineral on the level of initial values. This mode maintains the spectral and kinematic characteristics of anomalously luminescent diamonds at the wanted level to ensure extraction of diamonds to concentrate.
DS202004-0503
2020
Chasse, M., Blanchard, M., Cabaret, D., Vantelon, D., Juan, A., Calas, G.First principles modeling of X-ray absorption spectra enlightens the process of scandium sequestration by iron oxides.American Mineralogist, Vol. 105, 7, 10.2138/am-2020-730Globalscandium

Abstract: Scandium is often associated with iron oxides in the environment. Despite the use of scandium as a geochemical tracer and the existence of world-class supergene deposits, uncertainties on speciation obscure the processes governing its sequestration and concentration. Here, we use first-principles approaches to interpret experimental K-edge X-ray absorption near-edge structure spectra of scandium either incorporated in or adsorbed on goethite and hematite, at concentrations relevant for the environment. This modeling helps to interpret the characteristic spectral features, providing key information to determine scandium speciation when associated with iron oxides. We show that scandium is substituted into iron oxides at low concentration without modifying the crystal structure. When scandium is adsorbed onto iron oxide surfaces, the process occurs through outer-sphere complexation with a reduction in the coordination number of the hydration shell. Considering available X-ray absorption spectra from laterites, the present results confirm that scandium adsorption onto iron oxides is the dominant mechanism of sequestration in these geochemical conditions. This speciation explains efficient scandium recovery through mild metallurgical treatments of supergene lateritic ores. The specificities of scandium sorption mechanisms are related to the preservation of adsorbed scandium in million-years old laterites. These results demonstrate the emerging ability to precisely model fine X-ray absorption spectral features of trace metals associated with mineral phases relevant to the environment. It opens new perspectives to accurately determine trace metals speciation from high-resolution spatially-resolved X-ray absorption near-edge structure spectroscopy in order to constrain the molecular mechanisms controlling their dynamics.
DS202005-0726
2020
Chattopadhyay, A., Bhownik, S. K., Roy, A.Tectonothermal evolution of the Central Indian tectonic zone and its implications for Proterozoic supercontinent assembly: the current status.Episodes ( IUGS), Vol. 43, 1, pp. 132-144.Indiacraton

Abstract: The Central Indian Tectonic Zone (CITZ) is a major E-W striking mobile belt dissecting the Indian Craton along which the northern and southern Indian cratonic blocks have joined to make the Greater Indian Landmass (GIL). CITZ has a long evolutionary history spanning over 1000 Myrs (2.1-0.9 Ga), overlapping with the assembly and dispersal of two supercontinents - Columbia and Rodinia. Despite a lot of recent work carried out on the CITZ, several outstanding issues remain, especially on the nature and timing of different orogenic events identified in the southern part of this mobile belt. The present contribution attempts to summarize the major petrological, structural and geochronological studies carried out in the CITZ and reappraise the tectonic models in the context of the current database. It is surmised that, while the northern part of CITZ records Paleoproterozoic (ca. 1.8 Ga) orogenic events, the southern part is dominated by a late Palaeoproterozoic-early Mesoproterozoic (ca.1.6-1.5 Ga) collision, followed by crustal extension, and finally a late Mesoproterozoic to early Neoproterozoic (ca. 1.04-0.93 Ga) collision that led to the final stitching of the North and South Indian cratonic blocks. Tectonic evolution of the CITZ is discussed in the context of the Proterozoic supercontinent cycle.
DS202009-1619
2020
Chaves, A.de O., Porcher, C.C.Petrology, geochemistry and Sm-Nd systematics of the Paleoproterozoic Itaguara retroeclogite from Sao Francisco/Congo craton: one of the oldest records of the modern style plate tectonics.Gondwana Research, in press available 44p. PdfSouth America, Brazileclogite

Abstract: Paleoproterozoic retrogressed eclogite (retroeclogite) occurs in the Itaguara Sequence included in the suture zone formed by collision between the Archean Divinópolis and Campo Belo/Bonfim Complexes in the southern São Francisco Craton, which represents the South American counterpart of the African Congo Craton. The Itaguara retroeclogite contains scarce omphacite and phengite but abundant garnet porphyroblasts embedded in a fine-grained, amphibole, biotite and quartz-bearing matrix. The 2.20 ± 0.05 Ga eclogitization event (garnet and whole rock Sm-Nd isochronic age) of the E-MORB protolith (TDM ~ 2.47 Ga) is recorded by omphacite formation during high-pressure prograde stage in amphibole eclogite facies due to ~70 km depth subduction process. Amphibole eclogite facies metamorphic peak stage of 17-20 kbar and 600-700 °C occurred during ~2.1 Ga continental collision. Tectonic exhumation-related decompression during collision probably triggered partial melting of the eclogitic rock. Finally, decompression late stage estimated between 5 and 8 kbar and 550-650 °C under amphibolite facies overprint during orogenic collapse was responsible for appearance of kelyphitic reaction rims (symplectite) around garnet crystals. As its Paleoproterozoic contemporary analogues from Congo Craton, the Itaguara retroeclogite is one of the oldest records of the modern-style plate tectonics.
DS202008-1378
2020
Chaves, M.L.de Sa.C., Caldas, J.P.de P., Andrade, K.W., Barbosa, M.S.C.Diamonds from the Santo Antonio River ( Delfinopolis Minas Gerais): probable relationship with the Canastra-3 kimberlite.REM, Int. Journal Ouro Preto, Vol. 73, 1, pp. 51-58. pdfSouth America, Brazil, Minas Geraisdeposit - Canastra-3

Abstract: The study identifies the Canastra-3 Kimberlite magnetic anomaly as the likely primary source of the alluvial diamonds recovered by "garimpeiros" in the Santo Antônio River basin (Delfinópolis, southwestern Minas Gerais). This conclusion is based on cumulative geophysical, hydrographic, metallogenical and mineral geochemistry evidences. The study area is located within fertile ground in the border of the São Francisco craton, close to other diamond primary sources and secondary deposits. This kimberlitic target is the only known in the Santo Antônio River basin. In addition, the known mineralized gravels of this river, worked in the past by "garimpeiros", have evidence of a short transport (angular pebbles and blocks), further evidence of a nearby source. The original data collected in the "Minas Gerais Aerogeophysical Survey Program" was processed and analyzed with the Euler Deconvolution method, implemented in software Oasis Montaj. With the exception of the Canastra-3 body anomaly, all others in the study were classified as non-kimberlitic. Recent sampling work on the weathered top of the Canastra-3 Kimberlite recovered indicator minerals, notably a high proportion of pyrope garnets of the G-10 type, which is unusual among the kimberlites of the region.
DS202006-0914
2020
Chayka, I.F., Sobolev, A.V., Izokh, A.E., Batanova, V.G., Krasheninnikov, S.P., Chervyakovskaya, M.V., Kontonikas-Charos, A., Kutyrev, A.V., Lobastov, B.M., Chervyakovskiy, V.S.Fingerprints of kamafugite-like magmas in Mesozoic lamproites of the Aldan Shield: evidence from olivine and olivine-hosted inclusions.Minerals, Vol. 10, 4, 30p.Russia, Siberiadeposit - Ryabinoviy

Abstract: Mesozoic (125-135 Ma) cratonic low-Ti lamproites from the northern part of the Aldan Shield do not conform to typical classification schemes of ultrapotassic anorogenic rocks. Here we investigate their origins by analyzing olivine and olivine-hosted inclusions from the Ryabinoviy pipe, a well preserved lamproite intrusion within the Aldan Shield. Four types of olivine are identified: (1) zoned phenocrysts, (2) high-Mg, high-Ni homogeneous macrocrysts, (3) high-Ca and low-Ni olivine and (4) mantle xenocrysts. Olivine compositions are comparable to those from the Mediterranean Belt lamproites (Olivine-1 and -2), kamafugites (Olivine-3) and leucitites. Homogenized melt inclusions (MIs) within olivine-1 phenocrysts have lamproitic compositions and are similar to the host rocks, whereas kamafugite-like compositions are obtained for melt inclusions within olivine-3. Estimates of redox conditions indicate that “lamproitic” olivine crystallized from anomalously oxidized magma (?NNO +3 to +4 log units.). Crystallization of "kamafugitic" olivine occurred under even more oxidized conditions, supported by low V/Sc ratios. We consider high-Ca olivine (3) to be a fingerprint of kamafugite-like magmatism, which also occurred during the Mesozoic and slightly preceded lamproitic magmatism. Our preliminary genetic model suggests that low-temperature, extension-triggered melting of mica- and carbonate-rich veined subcontitental lithospheric mantle (SCLM) generated the kamafugite-like melts. This process exhausted carbonate and affected the silicate assemblage of the veins. Subsequent and more extensive melting of the modified SCLM produced volumetrically larger lamproitic magmas. This newly recognized kamafugitic "fingerprint" further highlights similarities between the Aldan Shield potassic province and the Mediterranean Belt, and provides evidence of an overlap between "orogenic" and "anorogenic" varieties of low-Ti potassic magmatism. Moreover, our study also demonstrates that recycled subduction components are not an essential factor in the petrogenesis of low-Ti lamproites, kamafugites and leucitites.
DS202010-1832
2020
Chen, H., Leinenweber, K., Prakapenka, V., Kunz, M., Bechtel, H.A., Liu, Z., Shim, S-H.Phase transformation of hydrous ringwoodite to the lower-mantle phases and the formation of hydrous silica.American Mineralogist, Vol. 105, pp. 1342-1348. pdfMantlebridgmanite

Abstract: To understand the effects of H2O on the mineral phases forming under the pressure-temperature conditions of the lower mantle, we have conducted laser-heated diamond-anvil cell experiments on hydrous ringwoodite (Mg2SiO4 with 1.1 wt% H2O) at pressures between 29 and 59 GPa and temperatures between 1200 and 2400 K. Our results show that hydrous ringwoodite (hRw) converts to crystalline dense hydrous silica, stishovite (Stv) or CaCl2-type SiO2 (mStv), containing 1 wt% H2O together with Brd and MgO at the pressure-temperature conditions expected for shallow lower-mantle depths between approximately 660 to 1600 km. Considering the lack of sign for melting in our experiments, our preferred interpretation of the observation is that Brd partially breaks down to dense hydrous silica and periclase (Pc), forming the phase assembly Brd + Pc + Stv. The results may provide an explanation for the enigmatic coexistence of Stv and Fp inclusions in lower-mantle diamonds.
DS202007-1129
2020
Chen, Y., Gu, Y/.J., Heaman, L.M., Wu, L., Saygin, E., Hung, S-H.Reconciling seismic structures and Late Cretaceous kimberlite magmatism in northern Alberta, Canada.Geology, Vol. 48, in press available, 5 p. pdfCanada, Albertadeposit - Birch Mountain, Mountain Lake

Abstract: The Late Cretaceous kimberlites in northern Alberta, Canada, intruded into the Paleoproterozoic crust and represent a nonconventional setting for the discovery of diamonds. Here, we examined the origin of kimberlite magmatism using a multidisciplinary approach. A new teleseismic survey reveals a low-velocity (-1%) corridor that connects two deep-rooted (>200 km) quasi-cylindrical anomalies underneath the Birch Mountains and Mountain Lake kimberlite fields. The radiometric data, including a new U-Pb perovskite age of 90.3 ± 2.6 Ma for the Mountain Lake intrusion, indicate a northeast-trending age progression in kimberlite magmatism, consistent with the (local) plate motion rate of North America constrained by global plate reconstructions. Taken together, these observations favor a deep stationary (relative to the lower mantle) source region for kimberlitic melt generation. Two competing models, mantle plume and slab subduction, can satisfy kinematic constraints and explain the exhumation of ultradeep diamonds. The plume hypothesis is less favorable due to the apparent age discrepancy between the oldest kimberlites (ca. 90 Ma) and the plume event (ca. 110 Ma). Alternatively, magma generation may have been facilitated by decompression of hydrous phases (e.g., wadsleyite and ringwoodite) within the mantle transition zone in response to thermal perturbations by a cold slab. The three-dimensional lithospheric structures largely controlled melt migration and intrusion processes during the Late Cretaceous kimberlite magmatism in northern Alberta.
DS202007-1130
2020
Cheperov, A.I., Sonin, V.M., Zhimulev, E.I., Cheperov, A.A.Preservation conditions of CLIPPIR diamonds in the Earth's mantle in a heterogeneous metal-sulphide-silicate medium ( experimental modeling).Journal of Mineralogical and Petrological Sciences, Vol. 115, pp. 236-246. pdfMantlediamond inclusions

Abstract: The genesis of CLIPPIR diamonds (Cullinan-like, large, inclusion-poor, pure, irregular, and resorbed) have attracted much interest due to their possible crystallization from metal melt in deep horizons of the earth’s mantle. These diamonds usually show a pronounced resorption and irregular morphology. The present paper reports new experimental data on the dissolution of diamond crystals at high P-T parameters in Fe-S melt containing large amounts of silicate components (5-20 wt%). The experiments were performed using a split-sphere multi-anvil apparatus (BARS) at a pressure of 4 GPa and a temperature of 1450 °C. The samples consisted of natural diamond crystals placed in mixtures of Fe, S, and kimberlite. Wide variations in dissolution rates of diamond crystals were obtained. The absence of diamond dissolution in a heterogeneous medium indicates that the amount of solid silicate phases present in metal melt plays a role in the preservation of diamonds. This study demonstrated how diamonds can be stored in natural environments due to the heterogeneity of the medium composition which could insulate diamonds from the metal-sulphide melt. The obtained results improve our understanding of processes that lead to preservation of CLIPPIR diamonds in the deep mantle.
DS202008-1379
2020
Chepurov, A.I., Tomilenko, A.A., Sonin, V.M., Zhimulev, E.I., Bulbak, T.A., Cheperov, A.A., Sobolev, N.V.Interaction of an Fe-Ni melt with anthracene ( C14H10) in the presence of olivine at 3 Gpa: fluid phase composition.Doklady Earth Sciences, Vol. 492, pp. 333-337.MantleUHP, diamond

Abstract: The first results on the interaction between an Fe-Ni melt and anthracene (?14?10) in the presence of olivine at 3 GPa and 1500°? and on the study of the component composition of the fluid generated in this process are presented. The stability of aliphatic hydrocarbons in the implemented conditions is confirmed experimentally. It is established that, under these conditions, crystallization of high-magnesian olivines occurs (Fo = 97-98 mol %). The composition of the fluid is similar to the composition of the fluid from inclusions in synthetic diamonds. The conditions implemented in the experiment might have occurred at the early stages of the Earth’s evolution.
DS202004-0504
2020
Chernykh, S.V., Chernykh, A.V., Tarelkin, S., Didenko, S. ,Kondakov, M.N., Shcherbachev, K.D., Trifonova, E.V., Drozdova, T.E., Troschiev, S.Y., Prikhodko, D.D., Glybin, Y.N., Chubenko, A.P., Britvich, G.I., Kiselev, D.A., Polushin, N.I., Rabinovich, O.IHPHT single crystal diamond type IIa characterization for particle detectors.Physicsa Status Solidi , doi:10.1002/pssa.201900888GlobalHPHT

Abstract: Various samples of multisectoral high?pressure high?temperature (HPHT) single?crystal diamond plate (IIa type) (4?×?4?×?0.53?mm) are tested for particle detection applications. The samples are investigated by X?ray diffractometry, photoluminescence spectroscopy, Raman spectroscopy, Fourier?transform infrared, and visible/ultraviolet (UV) absorption spectroscopy. High crystalline perfection and low impurity concentration (in the {100} growth sector) are observed. To investigate detector parameters, circular 1.0 and 1.5?mm diameter Pt Schottky barrier contacts are created on {111} and {100} growth sectors. On the backside, a Pt contact (3.5?×?3.5?mm) is produced. The {100} growth sector is proved to be a high?quality detector: the full width at half maximum energy resolution is 0.94% for the 5.489?MeV 226Ra ??line at an operational bias of +500?V. Therefore, it is concluded that the HPHT material {100} growth sector is used for radiation detector production, whose quality is not worse than the chemical vapor deposition method or specially selected natural diamond detectors.
DS202007-1131
2020
Chisenga, C., Van der Meijde, M., Yan, J., Fadel. I., Atekwana, E.A., Steffen, R., Ramotoroko, C.Gravity derived crustal thickness model of Botswana: its implication for the Mw 6.5 April 3, 2017, Botswana earthquake. Tectonophysics, Vol. 787, 228479 12p. PdfAfrica, Botswanageophysics - gravity

Abstract: Botswana experienced a Mw 6.5 earthquake on 3rd April 2017, the second largest earthquake event in Botswana's recorded history. This earthquake occurred within the Limpopo-Shashe Belt, ~350 km southeast of the seismically active Okavango Rift Zone. The region has no historical record of large magnitude earthquakes or active faults. The occurrence of this earthquake was unexpected and underscores our limited understanding of the crustal configuration of Botswana and highlight that neotectonic activity is not only confined to the Okavango Rift Zone. To address this knowledge gap, we applied a regularized inversion algorithm to the Bouguer gravity data to construct a high-resolution crustal thickness map of Botswana. The produced crustal thickness map shows a thinner crust (35-40 km) underlying the Okavango Rift Zone and sedimentary basins, whereas thicker crust (41-46 km) underlies the cratonic regions and orogenic belts. Our results also show localized zone of relatively thinner crust (~40 km), one of which is located along the edge of the Kaapvaal Craton within the MW 6.5 Botswana earthquake region. Based on our result, we propose a mechanism of the Botswana Earthquake that integrates crustal thickness information with elevated heat flow as the result of the thermal fluid from East African Rift System, and extensional forces predicted by the local stress regime. The epicentral region is therefore suggested to be a possible area of tectonic reactivation, which is caused by multiple factors that could lead to future intraplate earthquakes in this region.
DS202008-1380
2020
Choi, E., Fiorentini, M.L., Giuliani, A., Foley, S.F., Maas, R., Taylor, W.R.Subduction related petrogenesis of late Archean calc-alkaline lamprophyres in the Yilgarn craton, western Australia.Precambrian Research, Vol. 338, 105550, 18p. PdfAustralialamprophyres

Abstract: We present a comprehensive petrographic, mineralogical and geochemical study of calc-alkaline lamprophyres (CAL) from the Archean Yilgarn Craton, Western Australia. Previous studies have shown that the emplacement age of CAL from the Eastern Goldfields Superterrane of the Yilgarn Craton is ~2684 to ~2640 Ma. A new Rb/Sr mica age for a CAL sample in the Western Yilgarn is ~2070 Ma. Both Archean and Proterozoic CAL analysed in this study display porphyritic textures and contain phenocrysts of amphibole, minor clinopyroxene and biotite in a fine-grained groundmass dominated by feldspar. High MgO, Ni and Cr abundances (up to 11.9 wt%, 373 and 993 ppm. respectively) are consistent with derivation of primitive magmas from a mantle source. Enrichment in H2O, reflected in the abundance of magmatic amphibole and mica, combined with high whole-rock LILE, Th/Yb ratios and negative Nb-Ta anomalies in trace element patterns are consistent with a source that was metasomatised by hydrous fluids analogous to those generated by Phanerozoic subduction-related processes. Chondritic ?Nd and ?Hf signatures and Archean mantle-like Sr isotope signatures of the Late Archean CAL indicate that the fluid metasomatism required to explain their volatile and trace-element enriched composition shortly preceded partial melting (i.e. there was insufficient time to develop enriched radiogenic isotopic signatures). The concurrence of apparently juvenile radiogenic isotopes and fluid-related trace element compositions requires a geodynamic scenario whereby dehydration of a subducted slab triggered metasomatism of the overlying mantle wedge. Our findings therefore support a subduction setting at ~2.6-2.7 Ga along the eastern margin of the Yilgarn Craton. The CAL from the Western Yilgarn have similar compositions but enriched Sr-Nd-Hf isotopes compared to those in the Eastern Goldfields Superterrane. This signature is consistent with melting of lithospheric mantle domains previously enriched by subduction-related metasomatism. Hence, our study suggests the presence of a subduction setting in the Western Yilgarn during the Archean, which is consistent with previous geodynamic reconstructions. However, the geodynamic trigger for the early Proterozoic event that generated CAL magmatism in the Western Yilgarn is currently unclear.
DS202007-1132
2020
Choi, F.M., Fiorentini, M.L., Giuliani, A., Foley, S.F., Maas, R., Taylor, W.R.Subduction related tetrogenesis of late Archean calc-alkaline lamprophyres in the Yilgarn craton ( Western Australia).Precambrian Research, Vol. 338, 105550Australialamprophyres

Abstract: We present a comprehensive petrographic, mineralogical and geochemical study of calc-alkaline lamprophyres (CAL) from the Archean Yilgarn Craton, Western Australia. Previous studies have shown that the emplacement age of CAL from the Eastern Goldfields Superterrane of the Yilgarn Craton is ~2684 to ~2640 Ma. A new Rb/Sr mica age for a CAL sample in the Western Yilgarn is ~2070 Ma. Both Archean and Proterozoic CAL analysed in this study display porphyritic textures and contain phenocrysts of amphibole, minor clinopyroxene and biotite in a fine-grained groundmass dominated by feldspar. High MgO, Ni and Cr abundances (up to 11.9 wt%, 373 and 993 ppm. respectively) are consistent with derivation of primitive magmas from a mantle source. Enrichment in H2O, reflected in the abundance of magmatic amphibole and mica, combined with high whole-rock LILE, Th/Yb ratios and negative Nb-Ta anomalies in trace element patterns are consistent with a source that was metasomatised by hydrous fluids analogous to those generated by Phanerozoic subduction-related processes. Chondritic ?Nd and ?Hf signatures and Archean mantle-like Sr isotope signatures of the Late Archean CAL indicate that the fluid metasomatism required to explain their volatile and trace-element enriched composition shortly preceded partial melting (i.e. there was insufficient time to develop enriched radiogenic isotopic signatures). The concurrence of apparently juvenile radiogenic isotopes and fluid-related trace element compositions requires a geodynamic scenario whereby dehydration of a subducted slab triggered metasomatism of the overlying mantle wedge. Our findings therefore support a subduction setting at ~2.6-2.7 Ga along the eastern margin of the Yilgarn Craton. The CAL from the Western Yilgarn have similar compositions but enriched Sr-Nd-Hf isotopes compared to those in the Eastern Goldfields Superterrane. This signature is consistent with melting of lithospheric mantle domains previously enriched by subduction-related metasomatism. Hence, our study suggests the presence of a subduction setting in the Western Yilgarn during the Archean, which is consistent with previous geodynamic reconstructions. However, the geodynamic trigger for the early Proterozoic event that generated CAL magmatism in the Western Yilgarn is currently unclear.
DS202011-2035
2020
Choudhary, B.R., Santosh, M., Ravi, S., Babu, E.V.S.S.K.Spinel and Ti-rich schorlomite from the Wajrakarur kimberlites, southern India: implications for metasomatism, diamond potential and orangeite lineage.Ore Geology Reviews, Vol. 126, 103727, 19p. PdfIndiadeposit - Wajrakarur

Abstract: Kl-4 and P-5 mesoproterozoic kimberlite pipes along with several other well-known diamondiferous (ca. 1110 Ma) kimberlites in the Wajrakarur kimberlite field (WKF) intruded into the cratonic roots of Eastern Dharwar craton (EDC) in southern India. The groundmass minerals of the kimberlites exhibit inequigranular texture contain spinel, Ti-rich schorlomite garnet, two generations of olivine (macrocrysts and groundmass microphenocrysts), phlogopite, perovskite, clinopyroxene (diopside), ilmenite (low Mn) and rare apatite. We identified three distinct spinel associations in Kl-4 and P-5: (i) fine-grained (<50 ?m) microcrysts in the groundmass; (ii) resorbed euhedral atoll spinel, consisting of titanomagnetite (magnesian-ulvospinel-magnetite to titanian-chrome-magnetite) which is isolated from the rim of magnetite by spongy lagoon phase of schorlomite, and (iii) larger chrome spinel macrocrysts/xenocrysts (>500 ?m). The schorlomite garnet in both P-5 and Kl-4 represents solid solution of schorlomite-pyrope-almandine-grossular. Additionally, Kl-4 contains another Cr-rich schorlomite-pyrope-almandine-uvarovite solid solution. Macrocrystic spinel exhibits distinct composition of chromium (Cr2O3 up to 59.62 wt%), and poor in TiO2 (<1.19 wt%). The high chromium spinel macrocrysts from Kl-4 are confirmed to be fragments of mantle xenocrysts and their composition falls within the diamond stability field. Atoll-textured epitaxial mantled resorbed spinel associated with schorlomite suggests that they formed through the replacement of spinel possibly through interaction of late residual fluids/melts in the final stages of crystallization of the kimberlite magma. The significant enrichment of Fe and Ti in schorlomite suggests the involvement of metasomatized sub-continental lithospheric mantle. It is also inferred that spinel immiscibility played an important role in the metasomatic replacement. The Ti-rich minerals have orangeitic affinity, similar to those in the Kaapvaal craton of South Africa, and suggest the high Ti-, high Ca- and the low Al-bearing nature of the parent magma (Group II kimberlites). The groundmass tetraferriphlogopite is Al- and Ba-poor and spinel show compositions straddling between magnesian ulvöspinel (Group I kimberlite) and titanomagnetite (Group II kimberlite) comparable with orangeite and lamproites. The results presented in this study suggest that the P-5 and Kl-4 has orengeitic or lamproitic affinity. Our findings can be useful as an indicator mineral in diamond prospecting.
DS202008-1381
2020
Choudhary, B.R., Santosh, M., Ravi, S., Babu, EVSSKIndicator mineral ( spinel) from the Wajrakarur kimberlites, southern India: implications for diamond potential and prospectivity.Goldschmidt 2020, 1p. AbstractIndiadeposit - Wajraarur, Kalandurg

Abstract: P-5 and Kl-4 Mesoproterozoic (ca. 1110 Ma) kimberlites from the Wajrakarur and Kalyandurg clusters, Eastern Dharwar craton (EDC), southern India are intruded into the diamondiferous cratonic roots. The spinel compositions is straddling between magnesian ulvöspinel (Group-1 kimberlite) and titanomagnetite (Group-2 kimberlite), comparable with orangeite and lamproites. These Ti-rich minerals have orangeitic affinity, as in the Kaapvaal craton of South Africa, and reflect the high Ti-, high Ca- and the low Al-bearing nature of the parent magma (Group II kimberlites). Larger chrome spinel macrocrysts/xenocrysts show >500 ?m of size with distinctly high chromium (Cr2O3 up to 59.62 wt%), and TiO2-poor (<1.19 wt%). The high chromium spinel macrocrysts represent fragments of mantle xenocrysts and their composition falls within the diamond stability field. The groundmass spinel has been replaced by Ti- schorlomite. The schorlomite garnet represents solid solution of schorlomite -pyrope -almandine-grossular and Crrich schorlomite -pyrope -almandine- uvarovite solid solution. These associations recommend that the schorlomite formed through the replacement of spinel through interaction of late residual fluids/melts in the final stages of crystallization of the kimberlite magma and enrichment in Fe and Ti in schorlomite suggests the involvement of metasomatized sub-continental lithospheric mantle. Present study may have useful application in diamond prospectivity.
DS202009-1620
2020
Choudhary, S., Sen, K., Kumar, S., Rana, S., Ghosh, S.Forsterite repricipitation and carbon dioxide entrapment in the lithospheric mantle during its interaction with carbonatitic melt: a case study from the Sung Valley ultramafic-alkaline-carbonatite complex, Meghalaya, NE India.Geological Magazine, 10.1017/S001675 68200000631 12p.Indiacarbonatites

Abstract: Carbonatite melts derived from the mantle are enriched in CO2- and H2O-bearing fluids. This melt can metasomatize the peridotitic lithosphere and liberate a considerable amount of CO2. Experimental studies have also shown that a CO2-H2O-rich fluid can form Fe- and Mg-rich carbonate by reacting with olivine. The Sung Valley carbonatite of NE India is related to the Kerguelen plume and is characterized by rare occurrences of olivine. Our study shows that this olivine is resorbed forsterite of xenocrystic nature. This olivine bears inclusions of Fe-rich magnesite. Accessory apatite in the host carbonatite contains CO2-H2O fluid inclusions. Carbon and oxygen isotopic analyses indicate that the carbonatites are primary igneous carbonatites and are devoid of any alteration or fractionation. We envisage that the forsterite is a part of the lithospheric mantle that was reprecipitated in a carbonatite reservoir through dissolution-precipitation. Carbonation of this forsterite, during interaction between the lithospheric mantle and carbonatite melt, formed Fe-rich magnesite. CO2-H2O-rich fluid derived from the carbonatite magma and detected within accessory apatite caused this carbonation. Our study suggests that a significant amount of CO2 degassed from the mantle by carbonatitic magma can become entrapped in the lithosphere by forming Fe- and Mg-rich carbonates.
DS202005-0727
2020
Chu, J.Origins of Earth's magnetic field remains a mystery. ( Jack Hills)MIT News, 4p. PdfAustraliaGeophysics - magnetics

Abstract: Microscopic minerals excavated from an ancient outcrop of Jack Hills, in Western Australia, have been the subject of intense geological study, as they seem to bear traces of the Earth’s magnetic field reaching as far back as 4.2 billion years ago. That’s almost 1 billion years earlier than when the magnetic field was previously thought to originate, and nearly back to the time when the planet itself was formed. But as intriguing as this origin story may be, an MIT-led team has now found evidence to the contrary. In a paper published today in Science Advances, the team examined the same type of crystals, called zircons, excavated from the same outcrop, and have concluded that zircons they collected are unreliable as recorders of ancient magnetic fields. In other words, the jury is still out on whether the Earth’s magnetic field existed earlier than 3.5 billion years ago.
DS202011-2036
2020
Chukanov, N.V., Aksenov, S.M., Pekov, I.V., Belakovskiy, D.I., Vozchikova, S.A., Britvin, S.N.Sergevanite, new eudialyte group mineral from the Lovozero alkaline massif, Kola Peninsula.The Canadian Mineralogist, Vol. 58, pp. 421-436.Russia, Kola Peninsuladeposit - Lovozero

Abstract: The new eudialyte-group mineral sergevanite, ideally Na15(Ca3Mn3)(Na2Fe)Zr3Si26O72(OH)3•H2O, was discovered in highly agpaitic foyaite from the Karnasurt Mountain, Lovozero alkaline massif, Kola Peninsula, Russia. The associated minerals are microcline, albite, nepheline, arfvedsonite, aegirine, lamprophyllite, fluorapatite, steenstrupine-(Ce), ilmenite, and sphalerite. Sergevanite forms yellow to orange-yellow anhedral grains up to 1.5 mm across and the outer zones of some grains of associated eudialyte. Its luster is vitreous, and the streak is white. No cleavage is observed. The Mohs' hardness is 5. Density measured by equilibration in heavy liquids is 2.90(1) g/cm3. Calculated density is equal to 2.906 g/cm3. Sergevanite is nonpleochroic, optically uniaxial, positive, with ? = 1.604(2) and ? = 1.607(2) (? = 589 nm). The infrared spectrum is given. The chemical composition of sergevanite is (wt.%; electron microprobe, H2O determined by HCN analysis): Na2O 13.69, K2O 1.40, CaO 7.66, La2O3 0.90, Ce2O3 1.41, Pr2O3 0.33, Nd2O3 0.64, Sm2O3 0.14, MnO 4.15, FeO 1.34, TiO2 1.19, ZrO2 10.67, HfO2 0.29, Nb2O5 1.63, SiO2 49.61, SO3 0.77, Cl 0.23, H2O 4.22, -O=Cl -0.05, total 100.22. The empirical formula (based on 25.5 Si atoms pfu, in accordance with structural data) is H14.46Na13.64K0.92Ca4.22Ce0.27La0.17Nd0.12Pr0.06Sm0.02Mn1.81Fe2+0.58Ti0.46Zr2.67Hf0.04Nb0.38Si25.5S0.30Cl0.20O81.35. The crystal structure was determined using single-crystal X-ray diffraction data. The new mineral is trigonal, space group R3, with a = 14.2179(1) Å, c = 30.3492(3) Å, V = 5313.11(7) Å3, and Z = 3. In the structure of sergevanite, Ca and Mn are ordered in the six-membered ring of octahedra (at the sites M11 and M12), and Na dominates over Fe2+ at the M2 site. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 7.12 (70) (110), 5.711 (43) (202), 4.321 (72) (205), 3.806 (39) (033), 3.551 (39) (220, 027), 3.398 (39) (313), 2.978 (95) (?forumla?), 2.855 (100) (404). Sergevanite is named after the Sergevan' River, which is near the discovery locality.
DS202007-1133
2020
Cimen, O., Corcoran, L., Kuebler, C., Simonetti, S.S., Simonetti, A.Geochemical, stable ( O, C, and B) and radiogenic ( Sr, Nd, Pb) isotopic data from the Eskisehir-Kizulxaoren ( NW-Anatolia) and the Malatya-Kuluncak ( E- central Anatolia) F-REE-Th deposits, Turkey: implications for nature of carbonate-hosted mineralizatiTurkish Journal of Earth Sciences, Vol. 29, doe:10.3906/yer-2001-7 18p. PdfEurope, TurkeyREE
DS202010-1833
2020
Clerici, A.M.C., Gomes, C.B.. De Min, A., Comin-Chiaramnti, P.Heavy minerals in the sediments from Paraguay rivers as indicators for diamond occurrences.Bol. Mus. Nac. Hist. Paraguay, , Vol. 20, 2, pp. 188-204. pdfSouth America, Paraguaygeochemistry

Abstract: After some works of Jaime Baez-Presse that quoted the presence of diamonds in Eastern Paraguay, we have perfprmed a whole sampling a study relative to the indicator mineral for diamonds. Indicator minerals are mineral species that, when appearing as transported grains in clastic sediments, indicate the presence in bedrock of a specific type of mineralization, hydrothermal alteration or lithology. Their physical and chemical characteristics, including a relatively high density (heavy minerals), facilitate their preservation and identification. The heavy minerals represent an important exploration method for detecting a variety of ore deposit types including diamond, gold, Ni-Cu, PGE, and so on.. One of the most significant events in the application of indicator mineral methods in the past was the diamond exploration. This paper provides an overview of indicator mineral methods, i.e. presence of Cr-diopside, Pyrope-rich garnet and Picroilmenite, for diamond exploration along the Eastern Paraguay river. Unfortunately the above heavy mineraks, generally associated to the diamonds, do not appear in Eastern Paraguay, excluding this Country as a potential source for the diamond as economic potential source.
DS202009-1621
2020
CNNThe Earth's core is younger than previously believed, according to new research.cnn.com, Aug. 25, 1/2p.MantleNews item - core
DS202002-0170
2019
Coldebella, B.Intensive (P-T-fO2) crystallization paramenters of Alto Paranaiba kimberlites and diamond instability: Tres Ranchos IV and Limeira I intrusions. ***PortThesis, University of Sao Paulo, August 53p. pdfSouth America, Brazildeposit - Tres Rabchos IV and limeira I

Abstract: Temperature (T), Pressure (P) and Oxygen fugacity (fO2) conditions were established for the Três Ranchos IV (diamond-bearing) and Limeira I (sterile) kimberlites of the Coromandel-Três Ranchos kimberlite field (Minas Gerais and Goiás, Brazil), Alto Paranaíba Alkaline Province (APAP), in order to draw a possible correlation between these intensive crystallization parameters and diamond instability. Both Três Ranchos IV and Limeira I are classified as coherent macrocrystic kimberlites, with an inequigranular texture formed by partially-to-fully altered olivine, phlogopite megacrysts up to 1 cm wide, macrocrysts (0.5-10 mm-sized), and crustal xenoliths set in a very fine groundmass composed mainly by perovskite, olivine, phlogopite, spinel, serpentine and carbonates identified in both intrusions. Apatite, ilmenite and monticellite are also present, but only in LM-I. Garnet macrocrysts and centimetric pyroxene xenocrysts phases are also present in Três Ranchos IV and Limeira I, respectively. The samples, strongly enriched in incompatible elements, are all MgO-rich, with high Mg# content. In order to apply different geotherm-and-oxybarometers in the calculation of P-T-fO2 conditions and to characterize the compositional variation of TR-IV and LM-I kimberlites, major, minor and trace-element concentrations of the main mineral phases were obtained by electron microprobe and LA-ICP-MS. Olivine cores of Limeira I present higher NiO, CaO and lower Cr2O3 contents than those from Três Ranchos IV. Mg# [(Mg/Mg+FeT), mol.%) ranges from 87 to 92 mol.% in TR-IV and from 83 to 92 mol.% in LM-I. The trace-element contents of olivine are similar in both kimberlites, the concentrations of Li, Zn and Mn appearing to be higher at olivine rims. In olivines from both intrusions, a pattern of enrichment in Zr, Ga, Nb, Sc, V, P, Al, Ti, Cr, Ca, and Mn in rims regions, is observed in the "melt trend" whereas enrichment in Zn, Co, Ni and possibly Na in cores regions, is found in the "mantle trend." In monticellite specimens from Limeira I, Mg# ranges from 72 to 93.8, while Ca/(Ca+Mg) ratios range from 35 to 58 mol.%. The perovskite composition in both LM-I and TR-IV remains close to the ideal CaTiO3, perovskite, but a variation from core endmembers (average Lop16 and Prv78) towards the rims (average Lop13 and Prv81) can be noticed in TR-IV samples. The highest concentrations of light rare earth elements (LREE), Nb, and Fe3+ are also observed in perovskites from the TR-IV kimberlite. Macrocrystic spinels of TR-IV kimberlite are Al-rich, whereas the groundmass crystals range from magnesiochromite to chromite. Ilmenites from LM-I are characterized by high MgO values at a given TiO2, with a large variation in Cr2O3. Pyrope garnets (62 to 73 mol.%) are present only in TR-IV, with Mg# ranging from 72 to 79 mol.%, being classified as lherzolitic (G9) and pyroxenitic (G4, G5). Diopside occurs as xenocrysts in LM-I and as microphenocrysts in TR-IV, with Mg# ranging from 85 to 91 and from 87 to 92, respectively. Xenocrystic diopsides from LM-I present higher MgO and FeO concentrations with monticellite grains along crystal rims and fractures. Temperature estimates for the LM-I kimberlite, obtained from the composition of diopside xenocrysts and Al-in olivine concentrations, ranging from 718 to 985 °C. Pressure ranges from 34 to 47 Kbar, as calculated using an empirical curve from a 37-mW/m2 geotherm proposed in the literature for Alto Paranaíba magmas. For TR-IV, temperature values ranging from 975 to 1270°C were obtained from Al-in olivine and Ni-in garnet concentrations. Pressures in the range from 18 to 34 Kbar were obtained from major element composition of garnet samples from TR-IV kimberlite. The fO2 of the TR-IV constrained by perovskite (kimberlite cognate phase) oxygen barometry ranges from NNO-7 to NNO+4, while for LM-I values range from NNO+6 to NNO-4. For the LM-I intrusion, monticellite, another cognate phase used as an oxybarometer, yielded a value range of NNO-4 to NNO+2. A change in the oxygen fugacity from cores towards rim recorded in the perovskites and the monticellite crystals is also noticed. The oxygen fugacity estimates of this work are the first ever calculated for magmas of the Alto Paranaíba Alkaline Province. All P-T-fO2 values obtained are consistent with literature data on the APAP. Clinopyroxene xenocrysts from LM-I were classified as garnet-facies clinopyroxene, according to the compositions obtained in this work. Such results, along with pressure, and temperature data from and the presence of Mg-ilmenite in LM-I (known to be sterile), indicate that the kimberlite magma might have at least crossed the diamond stability field. The variation in oxygen fugacity observed in both kimberlites possibly reflects the instability of diamonds in these magmas since LM-I presents slightly higher oxidation conditions.
DS202007-1134
2020
Coldebella, B., Azzone, R.G., Chmyz, L., Ruberti, E., Svisero, D.P.Oxygen fugacity of Alto Paranaiba kimberlites and diamond stability: Tres Ranchos IV and Limeira I intrusions.Brazilian Journal of Geology, Vol. 50, 1, 15p.South America, Brazildeposit - Tres Ranchos IV

Abstract: Oxygen fugacity (ƒO2) conditions were established for Três Ranchos IV (TR-IV, diamond-bearing) and Limeira I (LM-I, barren) kimberlite intrusions, in Alto Paranaíba Alkaline Province, to constrain a possible correlation between fO2 and diamond instability. Temperature and pressure estimates obtained from the xenocryst assemblage composition are compatible up to garnet lherzolite levels. It suggests that both intrusions could cross the diamond-stability field. The ƒO2 of the TR-IV constrained by perovskite oxygen barometry presents an average value of -2.4 for ?NNO, with standard deviation of 1.30 (n = 120), whereas those calculations for LM-I have an average value of -1.31 for ?NNO, with standard deviation of 1.38 (n = 81). Considering these uncertainties, there is an important superposition of fO2 values for both intrusions, in which there is higher tendency of more reduced conditions for TR-IV. For the LM-I, an oxybarometer based on the composition of monticellite yielded a similar ?NNO range: -4.2 and +2.5. Some crystals and samples present trends towards more reduced conditions, while others display more oxidized conditions for each intrusion. Due to the superposition of ranges and absence of a preferential trend, the influence of fO2 for the possible instability of diamonds in the study area remains uncertain.
DS202005-0728
2020
Conceicao, F.T., Vasconcelos, P.M., Godoy, L.H., Navarro, G.R.B.40Ar/40Ar geochronological evidence for multiple magmatic events during the emplacement of Tapira alkaline-carbonatite complex, Minas Gerais, Brazil.Journal of South American Earth Sciences, Vol. 97, 102416, 7p. PdfSouth America, Brazil, Minas Geraiscarbonatite

Abstract: The Alto Parnaíba Igneous Province (APIP) is a voluminous magmatic province composed of various alkaline-carbonatite complexes emplaced in the Brasilia Mobile Belt during the Cretaceous. Relative timing of emplacement of silicate and carbonate magmas in most of these complexes remains mostly unresolved due to conflicting geochronological results. To determine the duration of magmatism and to test the possible existence of multiple magmatic events, we employ 40Ar/39Ar phlogopite single crystal dating to determine the history of magma emplacement at the Tapira alkaline-carbonatite complex, Minas Gerais, Brazil. The new single crystal data indicate at least two magmatic events during the emplacement of this complex, the first at > 96.2 ± 0.8 Ma and the second at 79.15 ± 0.6 Ma. The first igneous event was responsible for emplacement of the silicate plutonic series, while the second event corresponds to the emplacement of primarily carbonatitic magmas, generating metasomatic phlogopite alteration in bebedourites. The ages of intrusion and cooling of the alkaline-carbonatite complexes in the APIP must be investigated in other complexes to determine if intrusion intervals of ~17 Ma or more are common regionally. Protracted intrusive events, if related to magma generation by passage of South America over a stationary Trindade plume, requires complex ponding and lateral magma flow below a slow-moving continent.
DS202008-1382
2020
Conceicao, R.V., Marcon, V.H., Souza, M.R.W., Carniel, L.C., Quinteiro, R.V.S., Rovani, P., Mizusaki, A.M.P., Spitzenberger, M.S.Carbonatite/lamproite liquid imissibility in the Earth's mantle through the nefeline-diopside-kalsilite+-CO2, CH4, H2O diagram.Goldschmidt 2020, 1p. AbstractMantlelamproite

Abstract: The presence and speciation of volatile C-H-O elements in the silicate systems play an important role in the genesis of magmas on the Earth’s mantle, due to the fact that these elements, mainly in the form of H2O, CO2, CH4 and CxHy, decrease the solidi temperatures of source rocks, making magmatism possible in Earth’s present day thermal conditions [1]. Among those elements, carbon is the only element that changes its valence according to the oxygen fugacity (fO2) conditions of the environment, resulting in different speciation, as: CO3 -2, CO2, Cgraphite/diamond, CH4 or heavier hydrocarbons. In the present work, we are determining phase stability of minerals, water, CO2 and CH4 in the system Nefeline-Kalsilite-Diopside. Our experiments are conducted under 4.0 GPa and temperatures up to 1300°C, using a 1000 tonf hydraulic press coupled with toroidal chambers. Preliminary experiments performed at 1300°C and 4.0GPa (initial composition in the Olivine-Quartz- Kalsalite/Nepheline system: 40mol% Ol90, 40mol% Nph50Kls50 and 20mol% Qz, PH2O,CO2=Ptotal) resulted in the formation of forsterite (Fo90) in equilibrium with phlogopite (Phl), melt and volatile phases (CO2 and CH4). Closer to the Diopside vertice, the addition of CO3 to the sample resulted in a imisibility of a carbonatitic and a silicatic melt, in which the carbonititic melt is enriched in sodium, while the silcate melt is enriched in potassium. Appart from that, experiments in different parts of the diagram suggest compositions from nephelinite-kalsilitite to lamproites composition for the silicate melt in equilibrium with diopside (solid solution with omphacite) and phlogopite. This work is a continuation of previous work in the anhydrous diagram and future works will provide the addition of CH4 as the volatile phase
DS202011-2037
2020
Condie, K.C.Revisiting the Mesoproterozoic.Gondwana Research, in press available 9p. pdfMantleNuna

Abstract: Many of the peculiar features of the Mesoproterozoic (1.6-1.0 Ga) are related to the assembly of the first supercontinent Nuna, and some may not be distinctive of this time period. A high frequency of A-type granites at 1.6-1.4 Ga may be due, in part, to sampling biases. The overall increase in frequency in A-type granites beginning at 1.9 Ga may track the propagation of plate tectonics especially in the Great Proterozoic Accretionary Orogen. Increases in alkali and related elements in granitoids at 2.4-2.0 Ga may reflect widespread propagation of subduction as plate tectonics spread around the globe, and increases in HREE, Nb, Ti and Sc in granitoids may be related to decreasing importance of restitic garnet in granitoid sources as Earth transitioned from TTG to calc-alkaline magmatic regimes. Related to possible global mantle events at 1.9, 1.0 and 0.6 Ga are peaks in frequency of LIP and zircon ages related to supercontinent assembly. Mesoproterozoic paleomagnetic data that require at least 12 passive margins during this time. An increase in plate speed with time since 2 Ga may reflect a decreasing viscosity contrast across the lithosphere-asthenosphere boundary in response to a cooling mantle or/and thinning of the lithosphere and corresponding increases in heat flux with time. A relatively constant 87Sr/86Sr of seawater between 1.9 and 1.0 Ga may have resulted from a balance between weathered juvenile and reworked crustal sources as well as enhanced seafloor weathering of oceanic basalts. Mostly positive eHf(t) in detrital zircons and eNd(t) granitoids during the Mesoproterozoic suggest significant juvenile crustal input. However, the sparsity of crust of this age today probably results from recycling of large volumes of continental crust into the mantle in peripheral accretionary orogens during the breakup of Nuna at 1.4-1.2 Ga.
DS202006-0915
2020
Conover, E.Physicists have harnessed the aloofness of quantum particles to create a new type of crystal. Pauli crystal ( not specific to diamonds just for interest)Science News, May 19, 2p.Europe, GermanyCrystallography
DS202010-1834
2020
Cordani, U.G., Colombo, C.G., Tassinari, C.G., Rolim, D.R.The basement of the Rio Apa craton in Mato Grosso do Sul ( Brazil and northern Paraguay): a geochronological correlation with the tectonic provinces of the south western craton.Researchgate, 2p. Abstract in englishSouth America, Brazil, Mato Grosso, Paraguaycraton

Abstract: The Rio Apa cratonic fragment crops out in Mato Grosso do Sul State of Brazil and in northeastern Paraguay. It comprises Paleo-Mesoproterozoic medium grade metamorphic rocks, intruded by granitic rocks, and is covered by the Neoprotero-zoic deposits of the Corumbá and Itapocumi Groups. Eastward it is bound by the southern portion of the Paraguay belt. In this work, more than 100 isotopic determina-tions, including U-Pb SHRIMP zircon ages, Rb-Sr and Sm-Nd whole-rock determina-tions, as well as K-Ar and Ar-Ar mineral ages, were reassessed in order to obtain a complete picture of its regional geological history. The tectonic evolution of the Rio Apa Craton starts with the formation of a series of magmatic arc complexes. The oldest U-Pb SHRIMP zircon age comes from a banded gneiss collected in the northern part of the region, with an age of 1950 23 Ma. The large granitic intrusion of the Alumiador Batholith yielded a U-Pb zircon age of 1839 33 Ma, and from the southeastern part of the area two orthogneisses gave zircon U-Pb ages of 1774 26 Ma and 1721 25 Ma. These may be coeval with the Alto Tererê metamorphic rocks of the northeastern corner, intruded in their turn by the Baía das Garças granitic rocks, one of them yielding a zircon U-Pb age of 1754 49 Ma. The original magmatic protoliths of these rocks involved some crustal component, as indicated by the Sm-Nd T DM model ages, between 1.9 and 2.5 Ga. Regional Sr isotopic homogenization, associated with tectonic deformation and medium-grade metamorphism occurred at approximately 1670 Ma, as suggested by Rb-Sr whole rock reference isochrons. Finally, at 1300 Ma ago, the Ar work indicates that the Rio Apa Craton was affected by widespread regional heating, when the temperature probably exceeded 350°C. Geographic distribution, age and isotopic signature of the lithotectonic units suggest the existence of a major suture separating two different tectonic domains, juxtaposed at about 1670 Ma. From that time on, the unified Rio Apa continental block behaved as one coherent and stable tectonic unit. It correlates well with the SW corner of the Amazonian Craton, where the medium-grade rocks of the Juruena-Rio Negro tectonic province, with ages between 1600 and 1780 Ma, were reworked at about 1300 Ma. Looking at the largest scale, the Rio Apa Craton is probably attached to the larger Amazonian Craton, and the actual configuration of southwestern South America is possibly due to a complex arrangement of allochthonous blocks such as the Arequipa, Antofalla and Pampia, with different sizes, that may have originated as disrupted parts of either Laurentia or Amazonia, and were trapped during later collisions of these continental masses.
DS202007-1135
2020
Corfu, F., Hegde, V.S.U-Pb systematics of the western Dharwar craton - glimpse of a billion year history of crustal evolution and relations to ancient supercratons.Journal of South American Earth Sciences, Vol. 102, 102659, 12p. PdfIndiageochronology

Abstract: The Dharwar Craton developed progressively over a billion years, through two main stages of crustal growth separated by a few-hundred million year long period of relative quiescence. The first stage between 3.4 and 3.0 Ga developed a proto-craton, which was considerably amplified during the second main stage between 2.7 and 2.4 Ga, through extensive magmatism, tectonism, and crustal consolidation. This paper reports U-Pb dating results obtained in four specific areas of the craton, with the data encompassing key moments in this long development. Rocks formed during the proto-craton stage include a 3089 Ma augen gneiss and a 2973 Ma evolved granite, the latter of which marks the final cratonization event of the proto-craton. The beginning of the second main stage is recorded in this study by 2650 Ma tonalite and trondhjemite, a 2623 Ma granite dyke cutting augen gneiss, and 2614, 2602 and 2588 Ma volcanic rocks. Titanite responded differently to the long evolution, as a function of location and type of overprint. It preserved an original 2973 Ma magmatic age in the west, but was reset and/or crystallized during secondary events in central domains of the craton, yielding ages between 2590 and 2360 Ma. A diorite stock intruded at 2207 Ma in the consolidated crust. It is correlated with the Anantapur-Kunigal mafic dyke swarm, one of a series of such events in the Dharwar Craton between 2.35 and 1.79 Ma. In terms of its overall evolution the Dharwar Craton has an affinity with the Slave clan, which includes the Wyoming and Zimbabwe cratons. It also matches many features in the evolution of the São Francisco Craton, a probable other member of Sclavia. This is in contrast to the Amazonian Craton, which has more affinity with the Superior clan.
DS202001-0005
2019
Cui, K., Wardle, B.L.Cited as reference to Ball paper on Black diamonds.ACS Applied Material Interfaces, Vol. 11, pp. 35212-35220Globalnanodiamond
DS202004-0505
2018
Cummings, D.I., Russell, H.A.J.Glacial dispersal trains in North America.Journal of Maps ( Taylor & Francis) on linkedin, Vol. 14, 2, pp. 476-485. pdfUnited States, CanadaGlaciation, geomorphology, map

Abstract: A map depicting glacial dispersal trains in North America has been compiled from published sources. It covers the Canadian Shield, the Arctic Islands, the Cordillera and Appalachian mountains, and Phanerozoic sedimentary basins south of the Shield. In total, 140 trains are portrayed, including those emanating from major mineral-deposit types (e.g. gold, base metal, diamondiferous kimberlite, etc.). The map took 10 years of on-and-off work to generate, and it culls data from over 150 years of work by government, industry, and academia. It provides a new tool to help companies find ore deposits in Canada: the trains are generally a better predictor of dispersal distance and direction than striations and streamlined landforms, the data typically depicted on surficial-geology maps, including the Glacial Map of Canada. It also gives new insight into sedimentation patterns and processes beneath ice sheets, a sedimentary environment that, because of its inaccessibility, remains poorly understood and controversial.
DS202002-0171
2019
Cutts, J.A., Smit, M., Spengler, D., van Roermind, H., Kooijman, E.Punctuated evolution of the Archean SCLM in sync with the supercontinent cycle. Western Gneiss ComplexAmericam Geophysical Union Fall meeting, 1p. AbstractEurope, Norwayeclogites, peridotites

Abstract: The preservation of Archean cratons is typically attributed to the presence of a highly-depleted and buoyant sub-continental lithospheric mantle (SCLM) that is equally old or older than its overlying crust. Time constraints on the formation and petrological evolution of the SCLM are key to investigating its long-term evolution and role in the formation and preservation of the continental crust. Nevertheless, such constraints are difficult to obtain as well-preserved samples of the SCLM are rare and typically lack conventional chronometric minerals. The history of SCLM rocks is typically inferred on the basis of model ages, many of which indicate an Archean origin; however, these dates are difficult to link to specific mineral assemblages or chemical signatures, and the petrological and dynamic processes that these represent. Garnet Lu-Hf geochronology is one of the few chronometers that could overcome this limitation. In this study, a refined method in Lu-Hf garnet chronology was applied to fragments of the Laurentian SCLM that are now exposed as orogenic peridotites in the ultrahigh-pressure domains of the Western Gneiss Complex, Norway. The peridotite bodies comprise a variety of unusually well-preserved rock types-from dunites that record decompression and melting at >350 km depth to fertile lithologies produced by melting and fluid metasomatism. Our internal isochron results from pyrope (after exsolution from majorite) in dunite samples yielded identical Neoarchean ages; these are the first-ever obtained for mantle garnet. The ages coincide with a time interval during which there was voluminous juvenile crust formation, indicating a link between this global process and the deeply sourced mantle upwellings that these samples represent. Internal isochrons from websterite-and clinopyroxenite-hosted pyrope yielded Meso-to Neoproterozoic ages that exactly match two distinct supercontinent break-up events in the overlying continental crust. Together, the new Lu-Hf results indicate that since its extraction during a period of widespread Archean crustal growth, the Laurentian SCLM appears to have largely been at petro-physical and chemical stasis and evolved only during short pulses that ran in sync with the supercontinent cycle.
DS202002-0172
2019
Czas, J., Pearson, D.G., Stachel, T., Kjarsgaard, B.A., Read, G.H.A Paleoproterozoic diamond bearing lithospheric mantle root beneath the Archean Sask craton, Canada.Lithos, DOI:10.1016/ j.lithos.2019.105301Canada, Saskatchewandiamond genesis

Abstract: The recently recognised Sask Craton, a small terrane with Archean (3.3-2.5 Ga) crustal ages, is enclosed in the Paleoproterozoic (1.9-1.8 Ga) Trans Hudson Orogen (THO). Only limited research has been conducted on this craton, yet it hosts major diamond deposits within the Cretaceous (~106 to ~95 Ma) Fort à la Corne (FALC) Kimberlite Field. This study describes major, trace and platinum group element data, as well as osmium isotopic data from peridotitic mantle xenoliths (n = 26) from the Star and Orion South kimberlites. The garnet-bearing lithospheric mantle is dominated by moderately depleted lherzolite. Equilibration pressures and temperatures (2.7 to 5.5 GPa and 840 to 1250 °C) for these garnet peridotites define a cool geotherm indicative of a 210 km thick lithosphere, similar to other cratons worldwide. Many of the peridotite xenoliths show the major and trace element signatures of carbonatitic and kimberlitic melt metasomatism. The Re-Os isotopic data yield TRD (time of Re-depletion) model ages, which provide minimum estimates for the timing of melt depletion, ranging from 2.4 to 0.3 Ga, with a main mode spanning from 2.4 to 1.7 Ga. No Archean ages were recorded. This finding and the complex nature of events affecting this terrane from the Archean through the Palaeoproterozoic provide evidence that the majority of the lithospheric mantle was depleted and stabilised in the Palaeoproterozoic, significantly later than the Archean crust. The timing of the dominant lithosphere formation is linked to rifting (~2.2 Ga - 2.0 Ga), and subsequent collision (1.9-1.8 Ga) of the Superior and Hearne craton during the Wilson cycle of the Trans Hudson Orogen.
DS202010-1835
2020
D'Agrella-Filho, M.S., Paul, Y.J., Antonio, P.Y.J., Bispo-Santos, F.The Precambrian drift history and paleogeography of Amazonia.Chapter 6,, Personen et al. ed. Precambrian Supercontinents, 99p. PdfSouth Americacraton

Abstract: Here, we reassess the paleomagnetic database for Amazonia and its geodynamic implications for supercontinents. According to paleomagnetic and geological data, Amazonia and West Africa joined at ca. 2.00 Ga defining a single long-lived block. This landmass eventually formed a part of the Columbia supercontinent together with Baltica and Laurentia between 1.78 and 1.42 Ga. For the formation of Rodinia paleomagnetic and geological data permit three different models: an oblique collision at ca. 1.2 Ga, a clockwise rotation of Amazonia/West Africa and Baltica from Columbia to Rodinia joining Laurentia at ca. 1.0 Ga, or a scenario where Amazonia/West Africa was a wandering block that did not take part in Columbia and collided with Laurentia to form Rodinia at ca. 1.0-0.95 Ga. The time Amazonia/West Africa joined Gondwana is also debatable, with contrasting geochronological and geological evidence supporting an early collision at 0.65-0.60 Ga or a late collision at 0.53-0.52 Ga.
DS202009-1622
2020
Dai, H-K., Zheng, J.P., Griffin, W.L., O'Reilly, S.Y., Xiong, Q., Ping, X., Chen, F-K., Lu, J.Pyroxenite xenoliths record complex melt impregnation in the deep lithosphere of the northwestern North China Craton.Journal of Petrology, 10.1093/petrology/egaa079 110p. PdfChinaxenoliths

Abstract: Transformation of refractory cratonic mantle into more fertile lithologies is the key to the fate of cratonic lithosphere. This process has been extensively studied in the eastern North China Craton (NCC) while that of its western part is still poorly constrained. A comprehensive study of newly-found pyroxenite xenoliths from the Langshan area, in the northwestern part of this craton is integrated with a regional synthesis of pyroxenite and peridotite xenoliths to constrain the petrogenesis of the pyroxenites and provide an overview of the processes involved in the modification of the deep lithosphere. The Langshan pyroxenites are of two types, high-Mg# [Mg2+/(Mg2++Fe2+)*100 = ? 90, atomic ratios] olivine-bearing websterites with high equilibration temperatures (880 ? 970 oC), and low-Mg# (70 ? 80) plagioclase-bearing websterites with low equilibration temperatures (550 ? 835 oC). The high-Mg# pyroxenites show trade-off abundances of olivine and orthopyroxene, highly depleted bulk Sr-Nd (?Nd?=?+11.41, 87Sr/86Sr = ?0.7034) and low clinopyroxene Sr isotopic ratios (mean 87Sr/86Sr = ?0.703). They are considered to reflect the reaction of mantle peridotites with silica-rich silicate melts derived from the convective mantle. Their depletion in fusible components (e.g., FeO, TiO2 and Na2O) and progressive exhaustion of incompatible elements suggest melt extraction after their formation. The low-Mg# pyroxenites display layered structures, convex-upward rare earth element patterns, moderately enriched bulk Sr-Nd isotopic ratios (?Nd = -14.20 ? -16.74, 87Sr/86Sr?=?0.7070 ? 0.7078) and variable clinopyroxene Sr-isotope ratios (87Sr/86Sr?=?0.706-0.711). They are interpreted to be crustal cumulates from hypersthene-normative melts generated by interaction between the asthenosphere and heterogeneous lithospheric mantle. Combined with studies on regional peridotite xenoliths, it is shown that the thinning and refertilization of the lithospheric mantle was accompanied by crustal rejuvenation and that such processes occurred ubiquitously in the northwestern part of the NCC. A geodynamic model is proposed for the evolution of the deep lithosphere, which includes long-term mass transfer through a mantle wedge into the deep crust from the Paleozoic to the Cenozoic, triggered by subduction of the Paleo-Asian ocean and the Late Mesozoic lithospheric extension of eastern Asia.
DS202008-1383
2020
Dalton, H., Giuiani, A., Phillips, D., Hergt, J., Maas, R., Woodhead, J., Matchan, E., O'Brien, H.Kimberlite magmatism in Finland: distinct sources and links to the breakup of Rodinia.Goldschmidt 2020, 1p. AbstractEurope, Finlanddeposit - Kuusamo

Abstract: The Karelian Craton in Finland is host to (at least) two distinct pulses of kimberlite magmatism. Twenty kimberlite occurrences have so far been discovered on the southwest margin of the craton at Kaavi-Kuopio and seven kimberlites are located in the Kuusamo area within the core of the craton. Comprehensive radiometric age determinations (U-Pb, Ar- Ar and Rb-Sr) reveal that all kimberlite activity was restricted to the Proterozoic. The Kaavi-Kuopio field was emplaced over a protracted period from ~610 to 550 Ma and is predated by the Kuusamo cluster that represents a relatively short pulse of magmatism at ~750 to 730 Ma. The emplacement of kimberlites globally has recently been linked to supercontinent reorganisation and we propose a similar scenario for these Finnish occurrences which, at the time of kimberlite emplacement, were situated on the Baltica paleo-continent. This land mass was contiguous with Laurentia in the Proterozoic and together formed part of Rodinia. The breakup of Rodinia is considered to have commenced at ~750 Ma and initiation of the opening of the Iapetus ocean at ~615 Ma. Contemporaneous with Kaavi-Kuopio magmatism, this latter period of Neoproterozoic crustal extension also includes the emplacement of kimberlites and related rocks in areas that were linked with Baltica as part of Rodinia - West Greenland and eastern North America. Both the initial and final periods of Rodinia’s breakup have been linked to mantle upwellings from the core-mantle boundary. We suggest that kimberlite magmatism in Finland was promoted by the influx of heat from mantle upwellings and lithospheric extension associated with the demise of Rodinia. Although both magmatic episodes are potentially linked to the breakup of Rodinia, whole-rock and perovskite radiogenic isotope compositions for the Kuusamo kimberlites (?Nd(i) +2.6 to +3.3, ?Hf(i) +3.1 to +5.6) are distinct from the Kaavi-Kuopio kimberlites (?Nd(i) -0.7 to +1.8, ?Hf(i) -6.1 to +5.2). The spread in Hf isotope compositions for the Kaavi-Kuopio magmas may be linked to variable assimilation of diverse mantle lithologies.
DS202002-0173
2019
Dalton, H., Giuliani, A., O'Brien, H., Phillips, D., Hergt, J.The role of lithospheric heterogeneity on the composition of kimberlite magmas from a single field: the case of Kaavi-Kuopio, Finland.Lithos, in press available, 61p. PdfEurope, Finlanddeposit - Kaavi-Kuopio

Abstract: Kimberlites are complex, ‘hybrid’ igneous rocks because their parental magmas entrain abundant crust- and mantle-derived components that can be readily assimilated during ascent to surface. Recent studies of olivine zonation patterns have shown compositional relationships between xenocrystic cores and magmatic rims, suggesting that kimberlite melt compositions might be controlled by assimilation of mantle material during emplacement. However, the nature and extent to which this process, as well as assimilation of crustal material, influences melt compositions within single kimberlite fields remains unclear. To address this issue, we have conducted a comprehensive geochemical and petrographic investigation of kimberlites from eight pipes in the Kaavi-Kuopio field in Finland, which were emplaced on the southern margin of the Karelian craton during the Neoproterozoic (~550-600 Ma). While magmatic olivine rims are usually homogeneous in composition within and between kimberlites of a single cluster and field (e.g., Lac de Gras), the Kaavi-Kuopio kimberlites appear to represent a unique case where there are statistically significant differences between the average Mg# of olivine rims in different pipes (89.9 ± 0.2 to 88.5 ± 0.3). Importantly, the Mg# of magmatic olivine rims exhibit a strong correlation with the Mg# of their mantle-derived xenocrystic cores. Furthermore, the compositions of olivine cores and rims exhibit a robust relationship with those of magmatic spinel (e.g., Mg#, TiO2 contents). These geochemical variations also align with the mineralogy of the kimberlites: whereby abundances of phlogopite and oxides (e.g., spinel) are negatively correlated with olivine rim Mg#. The robust relationship between entrained and assimilated lithospheric mantle material (i.e. olivine cores) and magmatic components (i.e. olivine rims, spinel, and groundmass mineral abundance), combined with numerical modelling suggests that up to 10 wt% assimilation of lithospheric mantle material has modified the compositions of the Kaavi-Kuopio kimberlites. These new data are also consistent with significant variations in the lithospheric mantle composition of the Karelian craton beneath the closely spaced (<10 km) kimberlites. Finally, in addition to mantle assimilation, formation of Si-Fe-rich mica in some of the examined kimberlites might be linked to late-stage increases in oxygen fugacity potentially enhanced by crustal contamination. This study shows for the first time that variable assimilation of mantle and crustal material can generate significant variations in kimberlites derived from seemingly similar sources.
DS202002-0174
2019
Dalton, H., Giuliani, A., O'Brien, H., Phillips, D., Maas, R. Petrogenesis of a hybrid cluster of evolved kimberlites and ultramafic lamprophyres in the Kuusamo area, Finland. Kasma 45, Kasma 45 south, Kasma 47, Kalettomanpuro, Kattaisenvaara, Dike 15 and LampiJournal of Petrology, in press available, 79p. PdfEurope, Finlanddeposit - Kuusamo

Abstract: Kimberlites are often closely associated, both in time and space, with a wide variety of alkaline ultramafic rock types; yet the question of a genetic relationship between these rock types remains uncertain. One locality where these relationships can be studied within the same cluster is the Karelian craton in Finland. In this study we present the first petrographic, mineral and whole-rock geochemical results for the most recently discovered kimberlite cluster on this craton, which represents an example of the close spatial overlap of kimberlites with ultramafic lamprophyres. The Kuusamo cluster incorporates seven bodies (Kasma 45, Kasma 45 south, Kasma 47, Kalettomanpuro (KP), Kattaisenvaara (KV), Dike 15 and Lampi) distributed along a 60?km NE-SW corridor. Hypabyssal samples from KV, KP, Kasma 45 and Kasma 47 consist of altered olivine macrocrysts and microcrysts and phlogopite phenocrysts in a groundmass of perovskite, apatite, spinel, ilmenite, serpentine, and calcite. These petrographic features combined with mineral (e.g., Mg-rich ilmenite, Al-Ba-rich, Ti-Fe-poor mica) and whole-rock incompatible trace element compositions (La/Nb = 0.8 ± 0.1; Th/Nb = 0.07 ± 0.01; Nb/U = 66 ± 9) are consistent with these rocks being classified as archetypal kimberlites. These Kuusamo kimberlites are enriched in CaO and poor in MgO, which combined with the absence of chromite and paucity of olivine macrocrysts and mantle-derived xenocrysts (including diamonds), suggest derivation from differentiated magmas after crystal fractionation. Samples from Lampi share similar petrographic features, but contain mica with compositions ranging from kimberlitic (Ba-Al-rich cores) to those more typical of orangeites/lamproites (increasing Si-Fe, decreasing Al-Ti-Ba), and have higher bulk-rock SiO2 contents than the Kuusamo kimberlites. These features, combined with the occurrence of quartz and titanite in the groundmass, indicate derivation from a kimberlite magma that underwent considerable crustal contamination. This study shows that crustal contamination can modify kimberlites by introducing features typical of alkaline ultramafic rock types. Dike 15 represents a distinct carbonate-rich lithology dominated by phlogopite over olivine, with lesser amounts of titaniferous clinopyroxene and manganoan ilmenite. Phlogopite (Fe-Ti-rich) and spinel (high Fe2+/Fe2++Mg) compositions are also distinct from the other Kuusamo intrusions. The petrographic and geochemical features of Dike 15 are typical of ultramafic lamprophyres, specifically, aillikites. Rb-Sr dating of phlogopite in Dike 15 yields an age of 1178.8 ± 4.1?Ma (2?), which is considerably older than the ?750?Ma emplacement age of the Kuusamo kimberlites. This new age indicates significant temporal overlap with the Lentiira-Kuhmo-Kostomuksha olivine lamproites emplaced ?100?km to the southeast. It is suggested that asthenospheric aillikite magmas similar to Dike 15 evolved to compositions akin to the Karelian orangeites and olivine lamproites through interaction with and assimilation of MARID-like, enriched subcontinental lithospheric mantle. We conclude that the spatial coincidence of the Kuusamo kimberlites and Dike 15 is likely the result of exploitation of similar trans-lithospheric corridors.
DS202010-1836
2020
Davaille, A., Romanowicz, B.Deflating the LLSVPs: bundles of mantle thermochemical plumes rather than thick stagnant "piles".Tectonics, e202TC006265 Vol. 39, 4, ? Mantletomography

Abstract: Based on SEMUCB?WM1 tomographic model, validated by other recent models, and fluid mechanics constraints, we show that the large low shear velocity provinces (LLSVPs) present at the base of the Earth's mantle beneath the Pacific and Africa do not extend as compact, uniform structures very high above the core?mantle boundary. In contrast, they contain a number of well?separated, low?velocity conduits that extend vertically throughout most of the lower mantle. The conceptual model of compact piles, continuously covering the areal extent of the LLSVPs, is therefore not correct. Instead, each LLSVP is composed of a bundle of thermochemical upwellings probably enriched in denser than average material. It is only when the tomographic model is filtered to long wavelengths that the two bundles of plumes appear as uniform provinces. Furthermore, the overall shape of the LLSVPs is probably controlled by the distribution of subducted slabs, and due to their thermochemical nature, the position of both LLSVPs and individual upwelling dynamics should be time dependent. There is also evidence for smaller plumes originating near the CMB in the faster than average regions of the voting map of Lekic et al. (2012, https://doi.org/10.1016/j.epsl.2012.09.014) as well as other, barely resolved, weaker plumes within the LLSVPs. These finer?scale features are starting to be resolved tomographically owing to improvements in full waveform modeling of body waves, including diffracted S waves (Sdiff) and waves multiply reflected on the core?mantle boundary (ScS) and their codas.
DS202006-0916
2020
Davey, S.C., Bleeker, W., Kamo, S.L., Vuollo, J., Ernst, R.E., Cousens, B.L.Archean block rotation in western Karelia: resolving dyke swarm patterns in metacraton Karelia-Kola for a refined paleogeographic reconstruction of supercraton Superia.Lithos, in press available 95p. PdfRussia, Kola Peninsulacraton

Abstract: Rifting, breakup, and subsequent collision related to the ca. 1.92-1.79?Ga Svecofennian orogeny fragmented and deformed the western margin of the Archean Karelia-Kola craton into four crustal blocks: Pudasjärvi, Iisalmi, Kuhmo, and Taivalkoski. Detailed quantification of Svecofennian deformation is limited due to poorly exposed basement geology and an as yet incomplete dyke swarm record. New U-Pb ID-TIMS geochronological results on baddeleyite and zircon are presented for three key mafic dykes from the Pudasjärvi block, namely the Uolevinlehto, Myllykangas, and Sipojuntti dykes. The age of the 325°-trending Uolevinlehto dyke is estimated at ca. 2400?±?12?Ma from discordant multigrain baddeleyite fractions, showing it to be younger than ca. 2450?Ma dykes across Karelia. The 350°-trending Myllykangas dyke has a minimum age of 2135.2?+?3.6/?3.7?Ma based on chemically abraded zircon. Results from single baddeleyite grains provide a precise upper intercept age of 2128.9?±?1.2?Ma for the 320°-trending Sipojuntti dyke. Our new U-Pb ages are integrated with those from the literature to define six major dyke swarms in the Pudasjärvi block: the WNW-trending ca. 2.45?Ga Pääjärvi, NW-trending ca. 2.40?Ga Uolevinlehto, NW-trending ca. 2.13-2.10?Ga Tohmajärvi, WNW-trending ca. 2.07?Ga Palomaa, NNW-trending ca. 1.98?Ga Paukkajanvaara and undated"East-West" dykes. Trends of contemporaneous dyke swarms in the Taivalkoski and Kuhmo blocks, however, are systematically offset by 35°. With subvertical dips, offset dyke swarms record 35° clockwise vertical-axis rotation of the Pudasjärvi block relative to the interior of Karelia, consistent with dextral transpression during the Svecofennian orogeny. Structural restoration of the Pudasjärvi blocks improves the constraints on regional dyke swarm patterns, and these are used to revise the position of the Karelia-Kola craton within the context of the paleogeographic reconstruction of supercraton Superia.
DS202002-0175
2019
de Araujo Neto, J.F., de Brito Barreto, S., Carrino, T.A., Muller, A., de Lira Santos, L.C.M.Mineralogical and gemological characterization of emerald crystals from Parana deposit, NE Brazil: a study of mineral chemistry, absorption and reflectance spectroscopy and thermal analysis.Brazil Journal of Geology ( www.scielo.br) ENG, 15p. PdfSouth America, Brazildeposit - Parana

Abstract: The Paraná deposit, located at Southwestern Rio Grande do Norte state, in Brazil, is one of the few emerald deposits found at Borborema Province. The mineralization occurs in phlogopite schists and actinolite-phlogopite schists associated with pegmatites and albitites within the Portalegre Shear Zone. Unlike other well-known Brazilian emerald deposits, the mineralogy of Paraná emeralds has remained poorly investigated for the last 40 years. In this study, we conducted mineralogical characterization of theses emeralds through gemological testing, mineral chemistry, absorption and reflectance spectroscopy, and thermal analysis. The Paraná emeralds are bluish-green colored, characterized by high refractive index, several two-phase fluid inclusions and mica is the main mineral inclusion. Electron probe microanalysis and laser ablation-inductively coupled plasma-mass spectrometry analyses detected the presence of Fe2+ (0.43-1.94 wt.% FeO) and Cr3+ (0.04-0.14 wt.% Cr2O3) as the main chromophores replacing octahedral Al3+ in the crystal structure. In addition, substantial amounts of MgO (0.40-2.72 wt.%), Na2O (0.50-1.81 wt.%), and Cs2O (0.07-0.44 wt.%) were also identified. The main causes for its coloration were attributed to Cr3+ absorption features in visible spectral range, which were corroborated by absorption and reflectance spectra. The presence of types I and II H2O at channel-sites was recorded in Fourier-transform infrared spectra and demonstrated by dehydration processes observed in different thermal and thermogravimetric analyses.
DS202002-0176
2019
De Hoog, J.C.M., Stachel, T., Harris, J.W.Trace element geochemistry of diamond hosted olivine inclusions from the Akwatia mine, West African Craton: implications for diamond paragenesis and geothermobarometry.Contributions to Mineralogy and Petrology, Vol. 174, (12) doi: 10.1007/s00410-019-1634-yAfrica, Ghanadeposit - Akwatia

Abstract: Trace-element concentrations in olivine and coexisting garnets included in diamonds from the Akwatia Mine (Ghana, West African Craton) were measured to show that olivine can provide similar information about equilibration temperature, diamond paragenesis and mantle processes as garnet. Trace-element systematics can be used to distinguish harzburgitic olivines from lherzolite ones: if Ca/Al ratios of olivine are below the mantle lherzolite trend (Ca/Al??300 µg/g Ca or?>?60 µg/g Na are lherzolitic. Conventional geothermobarometry indicates that Akwatia diamonds formed and resided close to a 39 mW/m2 conductive geotherm. A similar value can be derived from Al in olivine geothermometry, with TAl-ol ranging from 1020 to 1325 °C. Ni in garnet temperatures is on average somewhat higher (TNi-grt?=?1115-1335 °C) and the correlation between the two thermometers is weak, which may be not only due to the large uncertainties in the calibrations, but also due to disequilibrium between inclusions from the same diamond. Calcium in olivine should not be used as a geothermobarometer for harzburgitic olivines, and often gives unrealistic P-T estimates for lherzolitic olivine as well. Diamond-hosted olivine inclusions indicate growth in an extremely depleted (low Ti, Ca, Na, high Cr#) environment with no residual clinopyroxene. They are distinct from olivines from mantle xenoliths which show higher, more variable Ti contents and lower Cr#. Hence, most olivine inclusions in Akwatia diamonds escaped the refertilisation processes that have affected most mantle xenoliths. Lherzolitic inclusions are probably the result of refertilisation after undergoing high-degree melting first. Trivalent cations appear to behave differently in harzburgitic diamond-hosted olivine inclusions than lherzolitic inclusions and olivine from mantle xenoliths. Some divalent chromium is predicted to be present in most olivine inclusions, which may explain high concentrations up to 0.16 wt% Cr2O3 observed in some diamond inclusions. Strong heterogeneity of Cr, V and Al in several inclusions may also result in apparent high Cr contents, and is probably due to late-stage processes during exhumation. However, in general, diamond-hosted olivine inclusions have lower Cr and V than expected compared to mantle xenoliths. Reduced Na activity in depleted harzburgites limits the uptake of Cr, V and Sc via Na-M3+ exchange. In contrast, Al partitioning in harzburgites is not significantly reduced compared to lherzolites, presumably due to uptake of Al in olivine by Al-Al exchange.
DS202002-0177
2019
de Mamam Anzolin H., Dani, N., Remus, M.V.D., da Rocha Ribeiro, R., Nunes, A.R., Ruppel, K.M.V.Apatite multi-generations in the Tres Estradas carbonatite, southern Brazil: physical and chemistry meaning and implications to phosphate ore quality. Brazil Journal of Geology ( www.scielo.br) ENG, 17p. PdfSouth America, Brazildeposit - Tres Estradas

Abstract: Carbonatites were recently discovered in Southern Brazil, which increased the interest to evaluate the economic potential of these uncommon rocks, especially the Três Estradas Carbonatite. Carbonates are the dominant minerals of fresh rock followed by apatite, but the weathering process makes apatite abundant. We focused on apatite from the carbonatite using conventional petrography and electronic microscopy associated with microprobe, micro-Raman and Fourier-transform infrared spectroscopy. Results demonstrate the existence of four types. The primary type is associated with the rock crystallization and the subsequent three others are associated with weathering processes. The alteration mechanism was favorable for initial carbonate leaching and subsequent increase of phosphate with late precipitation of three new apatite generations. The deduced model involves long exposure during polycyclic climate changes, intercalating periods of warm dry with humid climate. The apatite types differ chemically and morphologically and have distinctive characteristics that are suitable to be used to differentiate them. These properties should be considered in future planes of industrial processes to transform apatite into single superphosphate, a basic input for fertilizer production.
DS202012-2211
2020
de Oliveira Chaves, A., Porcher, C.C.Petrology, geochemistry and Sm-Nd systematics of the Paleoproterozoic Itagurra retroeclogite from Sao Francisco/Congo craton: one of the oldest records of the modern-style plate tectonics.Gondwana Research, Vol. 87, pp. 224-237. pdfSouth America, Brazileclogites
DS202011-2038
2020
De Wit, M.Botswana's World Class Diamond Mines.https://www.youtube.com /watch?v=GoqjOMoUw3I, 1hr long Africa, BotswanaHistory
DS202005-0729
2020
Decree, S., Cawthorn, G., Deloule, E., Mercadier, J., Frimmel, H., Baele, J-M.Unravelling the processes controlling apatite formation in the Phalaborwa Complex ( South Africa) based on combined cathodluminescence, LA-ICPMS and in-situ O and Sr isotope analyses.Contributions to Mineralogy and Petrology, Vol. 175, 34 31p. PdfAfrica, South Africacarbonatite

Abstract: The Phalaborwa world-class phosphate deposit (South Africa) is hosted by a Paleoproterozoic alkaline complex mainly composed of phoscorite, carbonatite, pyroxenitic rocks, and subordinate fenite. In addition, syenite and trachyte occur in numerous satellite bodies. New petrological and in-situ geochemical data along with O and Sr isotope data obtained on apatite demonstrate that apatite is in the principal host rocks (pyroxenitic rocks, phoscorite and carbonatite) formed primarily by igneous processes from mantle-derived carbonatitic magmas. Early-formed magmatic apatite is particularly enriched in light rare earth elements (LREE), with a decrease in the REE content ascribed to magma differentiation and early apatite fractionation in isolated interstitial melt pockets. Rayleigh fractionation favored a slight increase in ?18O (below 1%) at a constant Sr isotopic composition. Intrusion of fresh carbonatitic magma into earlier-formed carbonatite bodies locally induced re-equilibration of early apatite with REE enrichment but at constant O and Sr isotopic compositions. In fenite, syenite and trachyte, apatite displays alteration textures and LREE depletion, reflecting interaction with fluids. A marked decrease in ?18O in apatite from syenite and trachyte indicates a contribution from ?18O-depleted meteoric fluids. This is consistent with the epizonal emplacement of the satellite bodies. The general increase of the Sr isotope ratios in apatite in these rocks reflects progressive interaction with the country rocks over time. This study made it possible to decipher, with unmatched precision, the succession of geological processes that led to one of the most important phosphate deposits worldwide.
DS202004-0506
2020
Delord, T., Huillery, P., Nicolas, L., Hetet, G.Spin-cooling of the motion of trapped diamond.Nature, March 23, in press available Globalnitrogen

Abstract: Observing and controlling macroscopic quantum systems has long been a driving force in quantum physics research. In particular, strong coupling between individual quantum systems and mechanical oscillators is being actively studied. Whereas both read-out of mechanical motion using coherent control of spin systems and single-spin read-out using pristine oscillators have been demonstrated, temperature control of the motion of a macroscopic object using long-lived electronic spins has not been reported. Here we observe a spin-dependent torque and spin-cooling of the motion of a trapped microdiamond. Using a combination of microwave and laser excitation enables the spins of nitrogen-vacancy centres to act on the diamond orientation and to cool the diamond libration via a dynamical back-action. Furthermore, by driving the system in the nonlinear regime, we demonstrate bistability and self-sustained coherent oscillations stimulated by spin-mechanical coupling, which offers the prospect of spin-driven generation of non-classical states of motion. Such a levitating diamond-held in position by electric field gradients under vacuum-can operate as a ‘compass’ with controlled dissipation and has potential use in high-precision torque sensing, emulation of the spin-boson problem15 and probing of quantum phase transitions. In the single-spin limit and using ultrapure nanoscale diamonds, it could allow quantum non-demolition read-out of the spin of nitrogen-vacancy centres at ambient conditions, deterministic entanglement between distant individual spins and matter-wave interferometry.
DS202004-0507
2020
Demarco, P.N., Masquelin, H., Prezzi, C., Muzio, R., Loureiro, J., Peel, E., Campal, N., Sanchez Bettucci, L. Aeromagnetic patterns in southern Uruguay: Precambrian- Mesozoic dyke swarms and Mesozoic rifting structural and tectonic evolution.Tectonophysics, in press available 40p. PdfSouth America, Uruguaygeophysics

Abstract: New high-resolution airborne magnetic data of Uruguay allowed constructing new maps concerning the spatial distribution of dyke swarms, main faults and other magnetic bodies, which compose the Uruguayan Shield. We combined geophysical analyses (vertical derivatives, upward continuation, Euler deconvolution), structural analyses of the magnetic maps and previous geological data in order to discriminate the main structural features of the Uruguayan Shield and contribute to a better understanding of its tectonic evolution. The magnetic maps revealed several outstanding features in the Uruguayan Shield. The Paleoproterozoic dyke swarm is larger, denser, more widespread and complex than originally thought, suggesting a possible plume origin. In addition, a new Mesozoic dyke swarm, as complex as the previous one, was identified crosscutting the Paleoproterozoic dyke swarm and the Neoproterozoic orogenic structures. Moreover, this swarm is connected to volcanic calderas in the Merín basin, and shows displacements along Neoproterozoic shear zones, in the magnetic maps, revealing its brittle reactivation during Mesozoic times. The new observations clarify how Proterozoic basement structures controlled the development of the Mesozoic rift. Paleoproterozoic dyke swarms were reactivated as normal faults and Neoproterozoic structures hindered the rift growth, deflecting the deformation in transcurrent movements. Meanwhile, the Mesozoic dyke swarm was developed in a perpendicular direction to the Neoproterozoic structures. Moreover, these findings contradict the current rift model for Uruguay and rise a new model in which the Mesozoic rift developed as two rift basins connected by a central transfer zone, generated by the reactivation of Dom Feliciano Belt structures, between the Sierra Ballena and Sarandí del Yí Shear Zones.
DS202010-1837
2020
den Hond, B.Cratons mark the spot for mineral bonanzas. * not specific to diamonds.EOS, https://doi.org/ 10.1029/2020EO148693Globalcraton

Abstract: The search for deposits of lead, zinc, copper, and nickel might soon become much less of a hit-and-miss activity. Instead of trying their luck over wide areas, mining companies should focus their efforts—and billions of dollars in exploration expenses—on the contours of thick, old pieces of lithosphere strewn across Earth’s continents: cratons. Lithospheric thickness can serve as a treasure map, according to Mark Hoggard, an Earth scientist at Harvard University and Columbia University, and his colleagues from the United Kingdom and Australia. They reported their findings in Nature Geoscience.
DS202010-1838
2020
Deng, L., Geng, X., Liu, Y., Zong, K., Zhu, L., Zhengwei, L., Hu, Z., Guodong, Z., Guangfu, C.Lithospheric modification by carbonatitic to alkaline melts and deep carbon cycle: insights from peridotite xenoliths of eastern China.Lithos, in press available 38p. PdfChinacarbonatite

Abstract: Carbonates in subducting oceanic slabs can survive beyond slab dehydration and be transferred into the deep mantle. Such deep carbon cycling plays a critical role in generating carbonatitic to alkaline melts. However, whether and how this process has influenced the lithospheric mantle still remains enigmatic. To address these issues, here we provide a detailed petrographic, in-situ chemical and Sr isotopic study on two mantle xenoliths (a wehrlite and a melt pocket-bearing peridotite) entrained by the Changle Miocene basalts from the eastern China. The Changle wehrlite contains carbonate melt inclusions and apatites and is merely enriched in clinopyroxene relative to the lherzolites. The clinopyroxenes are characterized by high (La/Yb)N (4.7-41) and low Ti/Eu (873-2292) ratios and equilibrated with carbonated silicate melt-like compositions. These petrographic and chemical features indicate that the wehrlite was formed by reaction between peridotite and carbonated silicate melts. On the other hand, the Changle melt pocket-bearing peridotite is suggested to have been produced by in-situ melting/breakdown of amphiboles of an amphibole-rich dunite. Low olivine Fo (~89), presence of amphiboles with high (La/Yb)N (~50) and low Ti/Eu (~1070) ratios suggest that such amphibole-rich dunite would have been formed by reaction of peridotite with hydrous alkaline basaltic melts from a carbonated mantle. Our data, combined with previously reported data of the Changle lherzolite xenoliths, unravel a series of mantle metasomatisms by carbonatitic to alkaline melts from carbonated mantle sources. The consistently high 87Sr/86Sr ratios (up to 0.7036) of the clinopyroxenes in both the wehrlites and lherzolites indicate the carbonate components in the mantle sources were derived from the stagnant Pacific slab within the Mantle Transition Zone. This study provides a fresh perspective on the role of deep carbon cycling from subducted oceanic slabs in chemical modification of intracontinental lithospheric mantle through reaction with different types of melts.
DS202009-1623
2019
Deng, L-P., Liu, Y-C., Yang, Y., Groppo, C., Rolfo, F., Gu, X-F.Anatexis of high-T eclogites in the Dabie orogen triggered by exhumation and post-orogenic collapse.European Journal of Mineralogy, Vol. 31, pp. 889-803. pdfChinaeclogite

Abstract: A combined study of detailed petrographic observation, mineral chemistry analysis and phase equilibrium modeling indicates that the high-temperature eclogites from the Dabie orogen, central China, experienced two episodes of anatexis: the first is phengite dehydration melting during the exhumation of deeply subducted slices, and the second is heating melting related to the post-orogenic collapse. Petrographic evidence and clues of the anatectic events include biotite + plagioclase + garnet ± amphibole intergrowth in matrix and biotite + plagioclase intergrowth within amphibole porphyroblast. Pressure-temperature (P-T) pseudosection and modal variation diagram indicate that the biotite + plagioclase + garnet ± amphibole in matrix was formed by the reactions phengite + clinopyroxene + quartz = melt + sanidine + garnet + plagioclase and later melt + sanidine + garnet = biotite + plagioclase, while the biotite + plagioclase intergrowths within poikiloblastic amphibole were formed by the reaction amphibole + muscovite + epidote = biotite + plagioclase + melt. In addition, the combination of petrological observations and P-T estimates suggests that the first melting event occurred at the late Triassic, while the second is related to the early Cretaceous mountain-root removal and subsequent asthenospheric upwelling and heat input. As the P-T paths of high-temperature/ultrahigh-pressure rocks have high probabilities to cross-cut phengite-melting curves, phengite melting during decompression may be a common process in these rocks. Moreover, the coexistence of multiple episodes of anatexis in a single tectonic slice suggests caution when identifying and dating partial melting in high-temperature/(ultra)high-pressure rocks.
DS202002-0178
2019
Dewey, J.F.Musings in tectonics.Canadian Journal of Earth Sciences, Vol. 56, pp. 1077-1094.MantleTectonic history

Abstract: I outline and discuss my career in the context of the history of structural geology and tectonics, the progressive developments that led to plate tectonics, the people who have encouraged and influenced me, the events that changed my life, my fifty six doctoral students who have taught me so much, and my principal interests in tectonics. I discuss, in particular, nine topics of special current interest: the evolution of Tibet, the geomorphology of the British Isles, transtension, the Precambrian, the complexities of plate boundary evolution, Appalachian-Caledonian evolution, ophiolites, the structure and strength of the lithosphere, and the subducting slab.
DS202004-0508
2020
Diggle, P.L., Dhaenens-Johannsson, U., Green, B., Welbourn, C.M., Tran Thi, T.N., Wang, W., Newton, M.E. Decoration of growth sector boundaries with single nitrogen vacancy centres in as-grown single crystal HPHT synthetic diamond.Diamond and Related Materials, arxiv.org 21p. Globalsynthetics

Abstract: Large (> 100 mm3), relatively pure (type II) and low birefringence single crystal diamond can be produced by high pressure high temperature (HPHT) synthesis. In this study we examine a HPHT sample of good crystalline perfection, containing less than 1 ppb (part per billion carbon atoms) of boron impurity atoms in the {001} growth sector and only tens of ppb of nitrogen impurity atoms. It is shown that the boundaries between {111} and {113} growth sectors are decorated by negatively charged nitrogen vacancy centres (NV?): no decoration is observed at any other type of growth sector interface. This decoration can be used to calculated the relative {111} and {113} growth rates. The bulk (001) sector contains concentrations of luminescent point defects (excited with 488 and 532 nm wavelengths) below 1011 cm?3 (10?3 ppb). We observe the negatively charged silicon-vacancy (SiV?) defect in the bulk {111} sectors along with a zero phonon line emission associated with a nickel defect at 884 nm (1.40 eV). No preferential orientation is seen for either NV? or SiV? defects, but the nickel related defect is oriented with its trigonal axis along the <111> sector growth direction. Since the NV? defect is expected to readily re-orientate at HPHT diamond growth temperatures, no preferential orientation is expected for this defect but the lack of preferential orientation of SiV? in {111} sectors is not explained.
DS202001-0006
2019
Dirlam, D.M., Rogers, C.L., Weldon, R.Gemstones in the era of the Taj Mahal and the Mughals.Gems & Gemology, Vol. 55, 3, pp. 294-319.Indiahistory

Abstract: The Taj Mahal evokes an image of a monumental building and reflecting pool—its classic view. But the Taj Mahal complex is much more than that. It is actually a series of beautiful buildings and gardens in Agra, India, built in the seventeenth century in loving memory of Mumtaz Mahal. This name, given by the Mughal emperor Shah Jahan to one of his brides, means “Chosen One of the Palace.” Famed for its architectural magnificence, the landmark holds additional significance for the gemologist. Upon closer investigation, one is impressed with the intricacies of the inlay of numerous gems to create thousands of designs throughout the buildings on the grounds. This article sheds light on the gems used in decorating the Taj Mahal and in the extraordinary jewelry collected by Shah Jahan and other Mughals. These gems often took intricate trade routes to Agra, which are also discussed, along with the craft used to create the inlays and the efforts undertaken to preserve this Wonder of the World.
DS202009-1624
2020
Dorfman, S.M., Potapkin, V., Lv, M., Greenberg, E., Kupenko, I., Chumakov, A.I., Bi, W., Alp, E.E., Liu, J., Magrez, A., Dutton, S.E., Cava, R.J., McCammon, C.A., Gillet, P.Effects of composition and pressure on electronic states of iron in bridgmanite.American Mineralogist, Vol. 105, pp. 1030-1039. pdfMantleredox

Abstract: Electronic states of iron in the lower mantle's dominant mineral, (Mg,Fe,Al)(Fe,Al,Si)O3 bridgmanite, control physical properties of the mantle including density, elasticity, and electrical and thermal conductivity. However, the determination of electronic states of iron has been controversial, in part due to different interpretations of Mössbauer spectroscopy results used to identify spin state, valence state, and site occupancy of iron. We applied energy-domain Mössbauer spectroscopy to a set of four bridgmanite samples spanning a wide range of compositions: 10-50% Fe/total cations, 0-25% Al/total cations, 12-100% Fe3+/total Fe. Measurements performed in the diamond-anvil cell at pressures up to 76 GPa below and above the high to low spin transition in Fe3+ provide a Mössbauer reference library for bridgmanite and demonstrate the effects of pressure and composition on electronic states of iron. Results indicate that although the spin transition in Fe3+ in the bridgmanite B-site occurs as predicted, it does not strongly affect the observed quadrupole splitting of 1.4 mm/s, and only decreases center shift for this site to 0 mm/s at ~70 GPa. Thus center shift can easily distinguish Fe3+ from Fe2+ at high pressure, which exhibits two distinct Mössbauer sites with center shift ~1 mm/s and quadrupole splitting 2.4-3.1 and 3.9 mm/s at ~70 GPa. Correct quantification of Fe3+/total Fe in bridgmanite is required to constrain the effects of composition and redox states in experimental measurements of seismic properties of bridgmanite. In Fe-rich, mixed-valence bridgmanite at deep-mantle-relevant pressures, up to ~20% of the Fe may be a Fe2.5+ charge transfer component, which should enhance electrical and thermal conductivity in Fe-rich heterogeneities at the base of Earth's mantle.
DS202003-0335
2020
Doucet, L.S., Li, Z-X., Ernst, R.E., Kirscher, U., Gamel El Dien, H., Mitchell, R.N.Coupled supercontinent-mantle plume events evidence by oceanic plume record.Geology, Vol. 48, pp. 159-163.Mantle, Africageodynamics

Abstract: The most dominant features in the present-day lower mantle are the two antipodal African and Pacific large low-shear-velocity provinces (LLSVPs). How and when these two structures formed, and whether they are fixed and long lived through Earth history or dynamic and linked to the supercontinent cycles, remain first-order geodynamic questions. Hotspots and large igneous provinces (LIPs) are mostly generated above LLSVPs, and it is widely accepted that the African LLSVP existed by at least ca. 200 Ma beneath the supercontinent Pangea. Whereas the continental LIP record has been used to decipher the spatial and temporal variations of plume activity under the continents, plume records of the oceanic realm before ca. 170 Ma are mostly missing due to oceanic subduction. Here, we present the first compilation of an Oceanic Large Igneous Provinces database (O-LIPdb), which represents the preserved oceanic LIP and oceanic island basalt occurrences preserved in ophiolites. Using this database, we are able to reconstruct and compare the record of mantle plume activity in both the continental and oceanic realms for the past 2 b.y., spanning three supercontinent cycles. Time-series analysis reveals hints of similar cyclicity of the plume activity in the continent and oceanic realms, both exhibiting a periodicity of ?500 m.y. that is comparable to the supercontinent cycle, albeit with a slight phase delay. Our results argue for dynamic LLSVPs where the supercontinent cycle and global subduction geometry control the formation and locations of the plumes.
DS202008-1384
2020
Doucet, L.S., Li, Z-X., Gamel El Dien, H., Pourteau, A., Murphy, B., Collins, W.J., Mattielli, N., Olierook, H.K.H., Spencer, C.J., Mitchell, R.N.Distinct formation history for deep mantle domains reflected in geochemical differences.Nature Geoscience, Vol. 13, pp. 511-515. pdfMantlegeochemistry

Abstract: The Earth’s mantle is currently divided into the African and Pacific domains, separated by the circum-Pacific subduction girdle, and each domain features a large low shear-wave velocity province (LLSVP) in the lower mantle. However, it remains controversial as to whether the LLSVPs have been stationary through time or dynamic, changing in response to changes in global subduction geometry. Here we compile radiogenic isotope data on plume-induced basalts from ocean islands and oceanic plateaus above the two LLSVPs that show distinct lead, neodymium and strontium isotopic compositions for the two mantle domains. The African domain shows enrichment by subducted continental material during the assembly and breakup of the supercontinent Pangaea, whereas no such feature is found in the Pacific domain. This deep-mantle geochemical dichotomy reflects the different evolutionary histories of the two domains during the Rodinia and Pangaea supercontinent cycles and thus supports a dynamic relationship between plate tectonics and deep-mantle structures.
DS202009-1625
2020
Doucet, L.S., Li, Z-X., GamelEl Dien, H., Pourteau, A., Murphy, J.B., Collins, W.J., Mattielli, N., Olierook, H.K.H., Spencer, C.J., Mitchell, R.N.Distinct formation history for deep mantle domains reflected in geochemical differences.Nature Geoscience, Vol. 13, July pp. 511-515. pdfMantlegeochemistry

Abstract: The Earth’s mantle is currently divided into the African and Pacific domains, separated by the circum-Pacific subduction girdle, and each domain features a large low shear-wave velocity province (LLSVP) in the lower mantle. However, it remains controversial as to whether the LLSVPs have been stationary through time or dynamic, changing in response to changes in global subduction geometry. Here we compile radiogenic isotope data on plume-induced basalts from ocean islands and oceanic plateaus above the two LLSVPs that show distinct lead, neodymium and strontium isotopic compositions for the two mantle domains. The African domain shows enrichment by subducted continental material during the assembly and breakup of the supercontinent Pangaea, whereas no such feature is found in the Pacific domain. This deep-mantle geochemical dichotomy reflects the different evolutionary histories of the two domains during the Rodinia and Pangaea supercontinent cycles and thus supports a dynamic relationship between plate tectonics and deep-mantle structures.
DS202007-1136
2020
Doucet, L.S., Xu, Y., Klaessens, D., Hui, H., Ionov, D.A., Mattielli, N.Decoupled water and iron enrichments in the cratonic mantle: a study on peridotite xenoliths from Tok, SE Siberian craton.American Mineralogist, Vol. 105, pp. 803-819.Russia, Siberia peridotites

Abstract: Water and iron are believed to be key constituents controlling the strength and density of the lithosphere and, therefore, play a crucial role in the long-term stability of cratons. On the other hand, metasomatism can modify the water and iron abundances in the mantle and possibly triggers thermo-mechanical erosion of cratonic keels. Whether local or large scale processes control water distribution in cratonic mantle remains unclear, calling for further investigation. Spinel peridotite xenoliths in alkali basalts of the Cenozoic Tok volcanic field sampled the lithospheric mantle beneath the southeastern margin of the Siberian Craton. The absence of garnet-bearing peridotite among the xenoliths, together with voluminous eruptions of basaltic magma, suggests that the craton margin, in contrast to the central part, lost its deep keel. The Tok peridotites experienced extensive and complex metasomatic reworking by evolved, Ca-Fe-rich liquids that transformed refractory harzburgite to lherzolite and wehrlite. We used polarized Fourier transform infrared spectroscopy (FTIR) to obtain water content in olivine, orthopyroxene (Opx), and clinopyroxene (Cpx) of 14 Tok xenoliths. Olivine, with a water content of 0-3 ppm H2O, was severely degassed, probably during emplacement and cooling of the host lava flow. Orthopyroxene (49-106 ppm H2O) and clinopyroxene (97-300 ppm H2O) are in equilibrium. The cores of the pyroxene grains, unlike olivine, experienced no water loss due to dehydration or addition attributable to interaction with the host magma. The water contents of Opx and Cpx are similar to those from the Kaapvaal, Tanzania, and North China cratons, but the Tok Opx has less water than previously studied Opx from the central Siberian craton (Udachnaya, 28-301 ppm; average 138 ppm). Melting models suggest that the water contents of Tok peridotites are higher than in melting residues, and argue for a post-melting (metasomatic) origin. Moreover, the water contents in Opx and Cpx of Tok peridotites are decoupled from iron enrichments or other indicators of melt metasomatism (e.g., CaO and P2O5). Such decoupling is not seen in the Udachnaya and Kaapvaal peridotites but is similar to observations on Tanzanian peridotites. Our data suggest that iron enrichments in the southeastern Siberian craton mantle preceded water enrichment. Pervasive and large-scale, iron enrichment in the lithospheric mantle may strongly increase its density and initiate a thermo-magmatic erosion. By contrast, the distribution of water in xenoliths is relatively “recent” and was controlled by local metasomatic processes that operate shortly before the volcanic eruption. Hence, water abundances in minerals of Tok mantle xenoliths appear to represent a snapshot of water in the vicinity of the xenolith source regions.
DS202001-0007
2019
Doucet, L-S., Li, Z-X., Kirscher, U., El Dien, H.G.Coupled supercontinent -mantle plume events evidenced by oceanic plume record.Geology, Vol. 48, 5p. Mantleplumes, hotspots
DS202008-1385
2020
Drenth, B.J., Souders, A.K., Schulz, K.J., Feinberg, J.M., Anderson, R.R., Chandler, V.W., Cannon, W.L., Clark, R.J.Evidence for a concealed Midcontinent Rift related northeast Iowa intrusive complex.Precambrian Research, in press available, 43p. PdfUnited States, Iowageophysics - seismics

Abstract: Large amplitude aeromagnetic and gravity anomalies over a ~9500 km2 area of northeast Iowa and southeast Minnesota have been interpreted to reflect the northeast Iowa intrusive complex (NEIIC), a buried intrusive igneous complex composed of mafic/ultramafic rocks in the Yavapai Province (1.8-1.7 Ga). Hundreds of meters of Paleozoic sedimentary cover and a paucity of basement drilling have prevented detailed studies of the NEIIC. Long considered, but not proven, to be related to the ~1.1 Ga Midcontinent Rift System (MRS), the NEIIC is comparable in areal extent to the richly mineralized Duluth Complex and is similarly located near the margin of the MRS. New geochronological and geophysical data together support an MRS affinity for the NEIIC. A dike swarm imaged in aeromagnetic data is cut by intrusions of the NEIIC, and a new apatite U-Pb date of ~1170 Ma on one of the dikes thus represents a maximum age for the NEIIC. A minimum age constraint is suggested by (1) large-volume magmatism associated with the MRS that was the last such event to affect the region; and (2) the presence of reversely magnetized dikes, similar in character to MRS-related dikes elsewhere, that cut several intrusions of the NEIIC. The NEIIC is largely characterized by the presence of multiple zoned intrusions, many of which contain large volumes of mafic-ultramafic rocks and have strong geophysical similarities to alkaline intrusive complexes elsewhere, including the MRS-related Coldwell Complex of Ontario. The largest of the zoned intrusions are ~40 km in diameter and are interpreted to have thicknesses of many kilometers. Suspected faults, alignments of intrusions, and intrusive margins tend to be aligned along northwest and northeast trends that match the trends of the Belle Plaine fault zone and Fayette structural zone, both previously interpreted as pre-MRS, possibly lithospheric-scale discontinuities that may have controlled NEIIC emplacement. These interpretations collectively imply notable potential for the NEIIC to host several different types of undiscovered base metal and critical mineral deposits.
DS202010-1839
2020
Drenth, N.J., Souders, A.K., Schulz, K.J., Feinberg, J.M., Anderson, R.R., Chandler, V.W., Cannon, W.F., Clark, R.J.Evidence for a concealed Midcontinent Rift related northeast Iowa intrusive complex.Precambrian Research, Vol. 347, 105845, 23p. PdfUnited States, Iowageochronology, geophysics - gravity

Abstract: Large amplitude aeromagnetic and gravity anomalies over a ~9500 km2 area of northeast Iowa and southeast Minnesota have been interpreted to reflect the northeast Iowa intrusive complex (NEIIC), a buried intrusive igneous complex composed of mafic/ultramafic rocks in the Yavapai Province (1.8-1.7 Ga). Hundreds of meters of Paleozoic sedimentary cover and a paucity of basement drilling have prevented detailed studies of the NEIIC. Long considered, but not proven, to be related to the ~1.1 Ga Midcontinent Rift System (MRS), the NEIIC is comparable in areal extent to the richly mineralized Duluth Complex and is similarly located near the margin of the MRS. New geochronological and geophysical data together support an MRS affinity for the NEIIC. A dike swarm imaged in aeromagnetic data is cut by intrusions of the NEIIC, and a new apatite U-Pb date of ~1170 Ma on one of the dikes thus represents a maximum age for the NEIIC. A minimum age constraint is suggested by (1) large-volume magmatism associated with the MRS that was the last such event to affect the region; and (2) the presence of reversely magnetized dikes, similar in character to MRS-related dikes elsewhere, that cut several intrusions of the NEIIC. The NEIIC is largely characterized by the presence of multiple zoned intrusions, many of which contain large volumes of mafic-ultramafic rocks and have strong geophysical similarities to alkaline intrusive complexes elsewhere, including the MRS-related Coldwell Complex of Ontario. The largest of the zoned intrusions are ~40 km in diameter and are interpreted to have thicknesses of many kilometers. Suspected faults, alignments of intrusions, and intrusive margins tend to be aligned along northwest and northeast trends that match the trends of the Belle Plaine fault zone and Fayette structural zone, both previously interpreted as pre-MRS, possibly lithospheric-scale discontinuities that may have controlled NEIIC emplacement. These interpretations collectively imply notable potential for the NEIIC to host several different types of undiscovered base metal and critical mineral deposits.
DS202002-0179
2020
D'Souza, R.J., Canil, D., Coogan, L.A.Geobarometry for spinel peridotites using Ca and Al in olivine.Contributions to Mineralogy and Petrology, Vol. 175, 12 pdfMantleperidotites

Abstract: Experiments were performed from 950 to 1250 °C and 1.5-2.4 GPa to determine the effect of pressure (P) on the temperature (T)-dependent partitioning of Al between olivine and spinel, using mixtures of natural spinel, olivine, clino- and ortho-pyroxene. When compared to 100 kPa experiments, the results show that there is no discernible effect of pressure on the Al-in-olivine thermometer at PT conditions relevant to the spinel peridotite facies. In our experiments with high-Cr spinel, we see no change in Al in olivine from starting values, likely due to the refractory nature of high-Cr spinel. Phase boundary flourescence prevented accurate quantification of Ca in olivine in the run products by electron microprobe analysis but measurements by laser ablation are consistent with the Köhler and Brey (Geochim Cosmochim Acta 54:2375-2388, 1990) Ca-in-olivine thermobarometer. The combination of Al (for T) and Ca (for P) in olivine thus has great potential for thermobarometry in spinel facies peridotites. As a test we apply this approach to published high precision Ca and Al data for olivine from the Ray Pic spinel peridotite xenoliths from the Massif Central (De Hoog et al. Chem Geol 270:196-215, 2010). Reassuringly, the calculated PT conditions (1.0-1.8 GPa; 900-1080 °C) for all samples lie beneath the Moho, within the spinel peridotite facies and fall along a geophysically constrained geotherm.
DS202007-1137
2020
Dube, J-M., Darbyshire, F.A., Liddell, M.V., Stephenson, R.Seismic anisotropy of the Canadian High Arctic: evidence from shear wave splitting.Tectonophysics, Vol. 789, 228524, 13p. PdfCanada, Arcticgeophysics - seismics

Abstract: The Canadian High Arctic preserves a long and complex tectonic history, including craton formation, multiple periods of orogenesis, extension and basin formation, and the development of a passive continental margin. We investigate the possible preservation of deformational structures throughout the High Arctic subcontinental lithosphere using measurements of seismic anisotropy from shear wave splitting at 11 seismograph stations across the region, including a N-S transect along Ellesmere Island. The majority of measurements indicate a fast-polarisation orientation that parallels tectonic trends and boundaries, suggesting that lithospheric deformation is the dominant source of seismic anisotropy in the High Arctic; however, a sub-lithospheric contribution cannot be ruled out. Beneath Resolute in the central Canadian Arctic, distinct back-azimuthal variations in splitting parameters can be explained by two anisotropic layers. The upper layer is oriented E-W and correlates with tectonic trends and the inferred lithospheric deformation history of the region. The lower layer has a ?NNE-SSW orientation and may arise from present-day convective mantle flow beneath locally-thinned continental lithosphere. In addition to inferences of anisotropic structure beneath the Canadian High Arctic, measurements from the far north of our study region suggest the presence of an anisotropic zone in the lowermost mantle beneath northwest Alaska.
DS202008-1386
2020
Duncombe, J.Earth's core is in the hot seat.Eos, 101, doi,org./10.1029 /EO145531 June 24, MantleCore age

Abstract: How old is Earth’s inner core? High-pressure and high-temperature experiments suggest that our planet’s inner furnace may be much younger than expected.
DS202008-1387
2020
Duncombe, J.The ticking time bomb of Arctic permafrost.Eos, 101, doi,org./10.1029/EO1414607 June 24, Russiapermafrost

Abstract: Arctic infrastructure is under threat from thawing permafrost.
DS202012-2212
2019
Dupuy, D.C., Phillips, J.C.Selecting a diamond verification instrument based on the results of the Assure program: an initial analysis.Journal of Gemmology, Vol. 36, pp. 606-619.Globalluminescence

Abstract: Recently, the rapid growth in synthetic diamond production-particularly in melee sizes-and the salting of melee parcels with synthetics have generated a commensurate increase in the need for diamond verification instruments (DVIs). Ongoing independent third-party testing of these instruments is being done through the Assure Program. DVI performance is tested in a UL laboratory using carefully developed testing standards and sample sets (i.e. natural diamonds and as-grown and treated synthetics, as well as simulants as appropriate). The initial phase of testing was performed during latter 2018 and the first part of 2019, and as of July 2019 results for 16 widely available devices from 12 DVI manufacturers were published online in the Assure Directory (https://diamondproducers.com/assure/assure-directory). From these test results, the authors have evaluated several important parameters that will help users select the best instrument for their needs. Performance results from several additional DVIs are expected to be released in the near future, and further testing and publi-cation of the data will occur as new instruments are introduced and existing ones are updated.
DS202001-0008
2019
Dupuy, H., Phillips, J.G.Selecting a diamond verification: instrument based on the results of the Assure program: an initial analysis.Journal of Gemmology, Vol. 36, 7, pp. 606-619.Globaldiamond identification
DS202006-0917
2020
Dushyantha, N., Batapola, N., Ilankoon, I.M.S.K., Rohitha, S., Premasiri, R., Abeysinghe, B., Ratnayake, N., Dissanayake, K.The story of rare earth elements ( REES): occurrences, global distribution, genesis, geology, mineralogy and global production.Ore Geology Reviews, Vol. 122, 17p. PdfGlobalREE

Abstract: Rare earth elements (REEs) including fifteen lanthanides, yttrium and scandium are found in more than 250 minerals, worldwide. REEs are used in various high-tech applications across various industries, such as electrical and electronics, automotive, renewable energy, medical and defence. Therefore, the demand for REEs in the global market is increasing day by day due to the surging demand from various sectors, such as emerging economies, green technology and R&D sectors. Rare earth (RE) deposits are classified on the basis of their genetic associations, mineralogy and form of occurrences. The Bayan Obo, Mountain Pass, Mount Weld and China’s ion adsorption clays are the major RE deposits/mines in the world to date and their genesis, chronology and mineralogy are discussed in this review. In addition, there are other RE deposits, which are currently being mined or in the feasibility or exploration stages. Most of the RE resources, production, processing and supply are concentrated in the Asia-Pacific region. In this regard, China holds the dominancy in the RE industry by producing more than 90% of the current rare earth requirements. Thus, REEs are used as a powerful tool by China in trade wars against other countries, especially against USA in 2019. However, overwhelming challenges in conventional RE explorations and mining make secondary RE resources, such as electric and electronic waste (e-waste) and mine tailings as promising resources in the future. Due to the supply risk of REEs and the monopoly of the REEs market, REEs recycling is currently considered as an effective method to alleviate market fluctuations. However, economical and sustainable processing techniques are yet to be established to exploit REEs via recycling. Moreover, there are growing ecological concerns along with social resistance towards the RE industry. To overcome these issues, the RE industry needs to be assessed to maintain long-term social sustainability by fostering the United Nations sustainable development goals (SDGs).
DS202010-1840
2020
Dymshits, A., Sharygin, I., Malkovets, V., Yakovlev, I.V., Gibsher, A.A., Alifirova, T.A., Vorobei, S.S., Potapov, S.V., Garanin, V.K.Thermal state, thickness and composition of the lithospheric mantle beneath the Upper Muna kimberlite field, Siberian Craton, constrained by clinopyroxene xenocrysts and comparison with Daldyn and Mirny fields.Minerals, 10.1039/DOJA00308E 20p. PdfRussiadeposit - Muna

Abstract: To gain better insight into the thermal state and composition of the lithospheric mantle beneath the Upper Muna kimberlite field (Siberian craton), a suite of 323 clinopyroxene xenocrysts and 10 mantle xenoliths from the Komsomolskaya-Magnitnaya (KM) pipe have been studied. We selected 188 clinopyroxene grains suitable for precise pressure (P)-temperature (T) estimation using single-clinopyroxene thermobarometry. The majority of P-T points lie along a narrow, elongated field in P-T space with a cluster of high-T and high-P points above 1300 °C, which deviates from the main P-T trend. The latter points may record a thermal event associated with kimberlite magmatism (a “stepped” or “kinked” geotherm). In order to eliminate these factors, the steady-state mantle paleogeotherm for the KM pipe at the time of initiation of kimberlite magmatism (Late Devonian-Early Carboniferous) was constrained by numerical fitting of P-T points below T = 1200 °C. The obtained mantle paleogeotherm is similar to the one from the nearby Novinka pipe, corresponding to a ~34-35 mW/m2 surface heat flux, 225-230 km lithospheric thickness, and 110-120 thick "diamond window" for the Upper Muna field. Coarse peridotite xenoliths are consistent in their P-T estimates with the steady-state mantle paleogeotherm derived from clinopyroxene xenocrysts, whereas porphyroclastic ones plot within the cluster of high-T and high-P clinopyroxene xenocrysts. Discrimination using Cr2O3 demonstrates that peridotitic clinopyroxene xenocrysts are prevalent (89%) among all studied 323 xenocrysts, suggesting that the Upper Muna mantle is predominantly composed of peridotites. Clinopyroxene-poor or -free peridotitic rocks such as harzburgites and dunites may be evident at depths of 140-180 km in the Upper Muna mantle. Judging solely from the thermal considerations and the thickness of the lithosphere, the KM and Novinka pipes should have excellent diamond potential. However, all pipes in the Upper Muna field have low diamond grades (<0.9, in carats/ton), although the lithosphere thickness is almost similar to the values obtained for the high-grade Udachnaya and Mir pipes from the Daldyn and Mirny fields, respectively. Therefore, other factors have affected the diamond grade of the Upper Muna kimberlite field.
DS202010-1841
2020
Dymshits, A., Sharygin, I., Liu, Z., Korolev, N., Malkovets, V., Alifirova, T., Yakovlev, I., Xu, Y-G.Oxidation state of the lithospheric mantle beneath Komosomolskaya-Magnitnaya kimberlite pipe, Upper Muna field, Siberian craton.Minerals, Vol. 10, 9, 740 10.3390/ min10090740 24p. PdfRussiadeposit - Muna

Abstract: The oxidation state of the mantle plays an important role in many chemical and physical processes, including magma genesis, the speciation of volatiles, metasomatism and the evolution of the Earth’s atmosphere. We report the first data on the redox state of the subcontinental lithospheric mantle (SCLM) beneath the Komsomolskaya-Magnitnaya kimberlite pipe (KM), Upper Muna field, central Siberian craton. The oxygen fugacity of the KM peridotites ranges from ?2.6 to 0.3 logarithmic units relative to the fayalite-magnetite-quartz buffer (?logfO2 (FMQ)) at depths of 120-220 km. The enriched KM peridotites are more oxidized (?1.0-0.3 ?logfO2 (FMQ)) than the depleted ones (from ?1.4 to ?2.6 ?logfO2 (FMQ)). The oxygen fugacity of some enriched samples may reflect equilibrium with carbonate or carbonate-bearing melts at depths >170 km. A comparison of well-studied coeval Udachnaya and KM peridotites revealed similar redox conditions in the SCLM of the Siberian craton beneath these pipes. Nevertheless, Udachnaya peridotites show wider variations in oxygen fugacity (?4.95-0.23 ?logfO2 (FMQ)). This indicates the presence of more reduced mantle domains in the Udachnaya SCLM. In turn, the established difference in the redox conditions is a good explanation for the lower amounts of resorbed diamonds in the Udachnaya pipe (12%) in comparison with the KM kimberlites (33%). The obtained results advocate a lateral heterogeneity in the oxidation state of the Siberian SCLM.
DS202001-0009
2019
Eaton-Magana, S., Ardon, T., Breeding, C.M., Shigley, J.E.Natural color fancy white and fancy black diamonds: where color and clarity converge.Gems & Gemology, Vol. 55, 3, pp. 320-336.Globalreview

Abstract: Natural Fancy white and Fancy black diamonds are not routinely submitted to GIA for grading (fewer than 2,000 since 2008). These fancy-color diamonds are distinctive since the causes of color generally are not atomic-scale defects, but nanometer- to micrometer-sized inclusions that reduce the diamond’s transparency by scattering or absorbing light (some exceptions exist among Fancy black diamonds). To clarify, Fancy white diamonds are those rare stones colored by inclusions that give a “whitish” appearance, and are distinct from “colorless” diamonds on the D-to-Z scale. These two colors, often thought of as opposites in the color world, are grouped here as outliers within the colored diamond world. Both can be colored by inclusions so numerous the stone would fall below the I3 grade on the clarity scale, demonstrating that inclusions, often perceived as a negative quality factor, can create a distinctive appearance. Among the Fancy white diamonds examined for this study, the vast majority (82%) were type IaB, making them a rare subset of a rare diamond type. Based on prior geological research, these are surmised to be mostly sublithospheric in origin (i.e., forming more than 250 km below the earth’s surface). The Fancy white diamonds generally have a different chemistry from D-to-Z type IaB diamonds, with greater quantities of several hydrogen- and nickel-related defects. Among Fancy black diamonds, the major causes of color are either micrometer-sized dark crystal inclusions, nanometer-sized inclusions clustered into clouds, or a combination of the two. For these two colors of diamond, we summarize their gemological properties along with the absorption and luminescence spectra of a representative subset of diamonds from each color, examining how they deviate from the standard grading methodology. Because of their rarity, there has been very little systematic study of either of these color categories, and never a sample set of this quantity, which includes data for ~500 Fancy white and ~1,200 Fancy black diamonds.
DS202006-0918
2020
Eaton-Magana. S., McElhenny, G., Breeding, C.M., Ardon, T.Comparison of gemological and spectroscopic features in type IIa and Ia natural pink diamonds.Diamonds & Related Materials, Vol. 105, 13p. PdfMantlenitrogen

Abstract: The majority of natural pink diamonds have a color origin due to absorption from a broad 550?nm band that has been associated with plastic deformation. One consistent feature in the photoluminescence spectra of these pink diamonds is a wide emission band extending from ~600 to 750?nm, with a series of smaller oscillations overlaid on the larger emission band. This "pink emission band" is seen in diamonds colored by the 550?nm absorption band; the absorption band often, but not always, shows similar oscillations at ~600?nm (called the 609?nm system by previous researchers). This emission band served as a proxy for the 550?nm absorption band as we performed spatial mapping to chronicle the differences between the uniform coloration in type IIa pink diamonds and the pronounced banding in type Ia pink diamonds. We also used Raman spectroscopy to identify the internal crystal inclusions present in type IIa pink diamonds and determined that the majority have a sub-lithospheric origin.
DS202002-0180
2020
Eguchi, J., Seales, J., Dagupta, R.Great oxidation and Lomagundi events linked by deep cycling and enhanced degassing of carbon.Nature Geoscience, Vol. 13, pp. 71-76. Mantlecarbon

Abstract: For approximately the first 2?billion years of the Earth’s history, atmospheric oxygen levels were extremely low. It was not until at least half a billion years after the evolution of oxygenic photosynthesis, perhaps as early as 3?billion years ago, that oxygen rose to appreciable levels during the Great Oxidation Event. Shortly after, marine carbonates underwent a large positive spike in carbon isotope ratios known as the Lomagundi event. The mechanisms responsible for the Great Oxidation and Lomagundi events remain debated. Using a carbon-oxygen box model that tracks the Earth’s surface and interior carbon fluxes and reservoirs, while also tracking carbon isotopes and atmospheric oxygen levels, we demonstrate that about 2.5?billion years ago a tectonic transition that resulted in increased volcanic CO2 emissions could have led to increased deposition of both carbonates and organic carbon (organic?C)?via enhanced weathering and nutrient delivery to oceans. Increased burial of carbonates and organic?C would have allowed the accumulation of atmospheric oxygen while also increasing the delivery of carbon to subduction zones. Coupled with preferential release of carbonates at arc volcanoes and deep recycling of organic?C to ocean island volcanoes, we find that such a tectonic transition can simultaneously explain the Great Oxidation and Lomagundi events without any change in the fraction of carbon buried as organic?C relative to carbonate, which is often invoked to explain carbon isotope excursions.
DS202001-0010
2019
El Dien, H.G., Doucet, L.S., Li, Z-X.Global geochemical fingerprinting of plume intensity suggests coupling with the supercontinent cycle.Nature Communications, Vol 10, 1, doi.org/10.1038 /s41467-019-13300 8p. PdfMantleplumes, hotspots

Abstract: Plate tectonics and mantle plumes are two of the most fundamental solid-Earth processes that have operated through much of Earth history. For the past 300 million years, mantle plumes are known to derive mostly from two large low shear velocity provinces (LLSVPs) above the core-mantle boundary, referred to as the African and Pacific superplumes, but their possible connection with plate tectonics is debated. Here, we demonstrate that transition elements (Ni, Cr, and Fe/Mn) in basaltic rocks can be used to trace plume-related magmatism through Earth history. Our analysis indicates the presence of a direct relationship between the intensity of plume magmatism and the supercontinent cycle, suggesting a possible dynamic coupling between supercontinent and superplume events. In addition, our analysis shows a consistent sudden drop in MgO, Ni and Cr at ~3.2-3.0 billion years ago, possibly indicating an abrupt change in mantle temperature at the start of global plate tectonics.
DS202007-1138
2020
El Dien, H.G., Doucet, L.S., Murphy, J.B., Li, Z-X.Geochemical evidence for a widespread mantle re-enrichment 3.2 billion years ago: implications for global-scale plate tectonics.Scientific Reports, Vol. 10, 9461 8 pdfMantlemelting

Abstract: Progressive mantle melting during the Earth’s earliest evolution led to the formation of a depleted mantle and a continental crust enriched in highly incompatible elements. Re-enrichment of Earth’s mantle can occur when continental crustal materials begin to founder into the mantle by either subduction or, to a lesser degree, by delamination processes, profoundly affecting the mantle’s trace element and volatile compositions. Deciphering when mantle re-enrichment/refertilization became a global-scale process would reveal the onset of efficient mass transfer of crust to the mantle and potentially when plate tectonic processes became operative on a global-scale. Here we document the onset of mantle re-enrichment/refertilization by comparing the abundances of petrogenetically significant isotopic values and key ratios of highly incompatible elements compared to lithophile elements in Archean to Early-Proterozoic mantle-derived melts (i.e., basalts and komatiites). Basalts and komatiites both record a rapid-change in mantle chemistry around 3.2 billion years ago (Ga) signifying a fundamental change in Earth geodynamics. This rapid-change is recorded in Nd isotopes and in key trace element ratios that reflect a fundamental shift in the balance between fluid-mobile and incompatible elements (i.e., Ba/La, Ba/Nb, U/Nb, Pb/Nd and Pb/Ce) in basaltic and komatiitic rocks. These geochemical proxies display a significant increase in magnitude and variability after ~3.2 Ga. We hypothesize that rapid increases in mantle heterogeneity indicate the recycling of supracrustal materials back into Earth’s mantle via subduction. Our new observations thus point to a???3.2 Ga onset of global subduction processes via plate tectonics.
DS202004-0509
2020
Elling, R.P., Stein, S., Stein, C.A., Keller, G.R.Tectonics implications of the gravity signatures of the Midcontinent Rift and Grenville Front.Tectonophysics, Vol. 778, 228369, 6p. PdfUnited States, Canadamidcontinent rift

Abstract: North America's Midcontinent Rift (MCR) and Grenville Front (GF) jointly record aspects of the complex history of the assembly of Rodinia. The ~1100 Ma MCR, remaining from a failed major rifting event, is exposed along Lake Superior and well defined by gravity, magnetic, and seismic data. The GF, which results from collisions with Laurentia, is exposed in and identified by seismic and potential field data in Canada. In the eastern U.S., lineated gravity highs extending southward from Michigan to Alabama, along the trend of the front in Canada, have been interpreted either as a buried Grenville Front or as part of the MCR's east arm. We explore this issue by examining the gravity signatures of the MCR and GF. Both the MCR's arms have pronounced gravity highs, with the west arm's greater than the east arm's. Combining the gravity observations with seismic data suggests that the west arm contains 20-25 km thickness of volcanics, whereas the east arm contains 10-15 km of volcanics. Along the Grenville Front in Canada, thickened crust along the northern portion causes a broad gravity low, whereas the stacked thrusts along the southern portion cause essentially no gravity signature. Hence the lineated gravity highs in the eastern U.S. appear similar to those along the remainder of the MCR, and unlike those on either portion of the GF. These data favor the gravity anomalies traditionally interpreted as the Grenville Front in the eastern U.S. as instead being part of the MCR's east arm. A thrust sheet structure like that of the southern Canadian Grenville Front - which would have essentially no gravity effect - could also be present along the MCR's east arm, as implied by recent EarthScope seismic data.
DS202002-0181
2020
Elliott, B.A summary of the Slave geological province exploration development initiative - revitalizing mineral exploration and facilitating sustainable development in a a key economic region.Vancouver Kimberlite Cluster meeting, Jan. 23, 1/4p. AbstractCanada, Northwest Territoriesdata sets
DS202008-1388
2020
Eppelbaum, L., Ben-Avraham, Z., Katz, Y., Cloetingh, S., Kaban, M.Combined multifactor evidence of a giant lower mantle ring structure below the eastern mediterranean.Positioning, Vol. 11, pp. 11-32. pdf Africa, Arabiageophysics - gravity

Abstract: In the Arabian-Northern African region, interaction of the Nubian, Arabian and Eurasian plates and many small tectonic units is conspicuous. In order to better understand this interaction, we use satellite derived gravity data (retracked to the Earth’s surface) recognized now as a powerful tool for tectono-geodynamic zonation. We applied the polynomial approximation to the gravity data which indicated the presence of a large, deep ring structure in the eastern Mediterranean centered below the Island of Cyprus. Quantitative analysis of residual gravity anomaly provides an estimate of the deep anomalous body’s upper edge at a depth of about 1700 km. Computations of the residual gravity anomalies for the lower mantle also indicate presence of anomalous sources. The GPS vector pattern coinciding with the gravity trend implies counter clockwise rotation of this structure. Independent analyses of the geoid isolines map and seismic tomography data support the existence of a deep anomaly. Paleomagnetic data analysis from the surrounding regions confirms a counter clockwise rotation. Numerous petrological, mineralogical, geodynamical and tectonic data suggest a relation between this deep structure and near-surface processes. This anomaly sheds light on a number of phenomena including the Cyprus gravity anomaly, counter clockwise rotation of the Mesozoic terrane belt and asymmetry of basins along continental transform faults.
DS202012-2213
2021
Eppelbaum, L.V., Ben-Avraham, Z., Youri, K., Kaban, M.K.Giant quasi-ring structure if the African-Arabian junction: results derived from the geological-geophsyical data integration.Geotectonics, Mantletectonics

Abstract: The tectonic-geodynamic characteristics of the North African-Arabian region are complicated by interaction of numerous factors. To study this interaction, we primarily used the satellite gravity data (retracked to the Earth's surface), recognized as a powerful tool for tectonic-geodynamic zonation. The applied polynomial averaging of gravity data indicated the presence of a giant, deep quasi-ring structure in the Eastern Mediterranean, the center of which is located under the Island of Cyprus. Simultaneously, the geometrical center of the revealed structure coincides with the Earth's critical latitude of 35?. A quantitative analysis of the obtained gravitational anomaly made it possible to estimate the depth of the upper edge of the anomalous body as 1650?1700 km. The GPS vector map coinciding with the gravitational trend indicates counterclockwise rotation of this structure. Review of paleomagnetic data on the projection of the discovered structure into the earth's surface also confirms its counterclockwise rotation. The analysis of the geoid anomalies map and seismic tomography data commonly approve presence of this deep anomaly. The structural and geodynamic characteristics of the region and paleobiogeographic data are consistent with the proposed physical-geological model. Comprehensive analysis of petrological, mineralogical, and tectonic data suggests a relationship between the discovered deep structure and near-surface processes. The revealed geological deep structure sheds light on specific anomalous effects in the upper crustal layer, including the high-intensity Cyprus gravity anomaly, counterclockwise rotation of the Mesozoic terrane belt, configuration of the Sinai plate, and the asymmetry of sedimentary basins along the continental faults.
DS202002-0182
2019
Eppelbaum, L.V., Kutasov, I.M.Well drilling in permafrost regions: dynamics of the thawed zone. ( not specific to diamonds)Polar Research, Vol. 38, 3351 9p. PdfRussiapermafrost

Abstract: In the cold regions, warm mud is usually used to drill deep wells. This mud causes formation thawing around wells, and as a rule is an uncertain parameter. For frozen soils, ice serves as a cementing material, so the strength of frozen soils is significantly reduced at the ice-water transition. If the thawing soil cannot withstand the load of overlying layers, consolidation will take place, and the corresponding settlement can cause significant surface shifts. Therefore, for long-term drilling or oil/gas production, the radius of thawing should be estimated to predict platform stability and the integrity of the well. It is known that physical properties of formations are drastically changed at the thawing-freezing transition. When interpreting geophysical logs, it is therefore important to know the radius of thawing and its dynamics during drilling and shut-in periods. We have shown earlier that for a cylindrical system the position of the phase interface in the Stefan problem can be approximated through two functions: one function determines the position of the melting-temperature isotherm in the problem without phase transitions, and the second function does not depend on time. For the drilling period, we will use this approach to estimate the radius of thawing. For the shut-in period, we will utilize an empirical equation based on the results of numerical modelling.
DS202007-1139
2020
Eppelbaum, L.V., Youri, K.Significant tectono-geophysical features of the African-Arabian tectonic region: an overview.Geotectonics, Vol. 54, 2, pp. 266-283.AfricaArabian craton

Abstract: Satellite gravimetry is recognized now as powerful and reliable tool for regional tectono-geodynamic zonation. The studied region contains intricate geodynamical features (high seismological indicators, active rift systems and collision processes), richest structural arrangement (existence of mosaic blocks of oceanic and continental Earth’s crust of various age), and a number of high-amplitude gravity anomalies and complex geomagnetic pattern. The most hydrocarbon reserves and diamonds, gold, platinum and deposits occur in this region. Comprehensive analysis of satellite derived gravity data by different methodologies were used to develop a sequence of maps specifying crucial properties of the region deep structure. Combined analysis of the compiled gravity map and its transformations with obtained geological data allowed to detecting significant geotectonic features of lithosphere of the region. For instance, Zagros-Makran terrane was classified as a separately developing structural segment (element) of the Arabian craton. Detailed examination of numerous geological sources and their combined examination with the GPS pattern, paleomagnetic, tectonic, geoid isoline map, seismic and other data revealed some sophisticated tectono-geophysical feature apparently located in middle-lower mantle below the Arabian-African region.
DS202009-1626
2011
Eriksson, P.G., Lenhardt, N., Wright, D.T., Mazumder, R., Bumby, A.J.Late Neoarchean-paleoproterozoic supracrustal basin-fills of the Kaapvaal craton: relevance of the supercontinent cycle, the "Great Oxidation Event" and "Snowball Earth?". Note Date*** glaciationMarine and Petroleum Geology, Vol. 28, pp. 1385-1401.Africa, South Africageomorphology

Abstract: The application of the onset of supercontinentality, the “Great Oxidation Event” (GOE) and the first global scale glaciation in the Neoarchaean-Palaeoproterozoic as panacea-like events providing a framework or even chronological piercing points in Earth’s history at this time, is questioned. There is no solid evidence that the Kaapvaal craton was part of a larger amalgamation at this time, and its glacigenic record is dominated by deposits supporting the operation of an active hydrological cycle in parallel with glaciation, thereby arguing against the “Snowball Earth Hypothesis”. While the Palaeoproterozoic geological record of Kaapvaal does broadly support the GOE, this postulate itself is being questioned on the basis of isotopic data used as oxygen-proxies, and sedimentological data from extant river systems on the craton argue for a prolongation of the greenhouse palaeo-atmosphere (possibly in parallel with a relative elevation of oxygen levels) which presumably preceded the GOE. The possibility that these widespread events may have been diachronous at the global scale is debated.
DS202010-1842
2020
Ernst, W.G.How American Mineralogist and the Mineralogical Society of America influenced a career in mineralogy, petrology, and plate pushing, and thoughts on mineralogy's future role.American Mineralogist, Vol. 105, pp. 1285-1296.Globalhistory

Abstract: My geologic research began at Carleton College. I studied heavy minerals in some midcontinent orthoquartzites, publishing my very first paper in American Mineralogist in 1954. As a master's candidate at the University of Minnesota, I investigated igneous differentiation in a diabase-granophyre sill of the Duluth Gabbro Complex. Later, in a Ph.D. program at Johns Hopkins University, I became Joe Boyd's apprentice at the Geophysical Laboratory (GL), and for a time was phase-equilibrium god of the Na-amphiboles. Doctoral research earned me an offer of a UCLA assistant professorship as a mineralogist in 1960. There, I continued pursuing amphibole P-T stability relations in lab and field. My glaucophane phase equilibrium research would later be found to have instead crystallized Na-magnesiorichterite. However, amphibole research led me to map field occurrences of HP-LT (high P-low T) blueschists of the Franciscan Complex. Thus, when plate tectonics emerged in the late 1960s, I was deep in the subduction zone. My recent studies focused on the petrology and geochemistry of oceanic crustal rocks, Californian calc-alkaline arcs, and coesite ± microdiamond-bearing crustal margin rocks in various parts of Eurasia. Other works treated global mineral resources and population, mineralogy and human health, and early Earth petrotectonic evolution. I tried to work on important problems, but mainly studied topics that fired my interest. For the future, I see the existential challenge facing humanity and the biosphere as the imperative to stop our overdrafting of mineral resources. This will require reaching a dynamic equilibrium between the use and replenishment of near-surface resources (i.e., nutrients) essential for life. Earth scientists are planetary stewards, so we must lead the way forward in life-supporting mineral usage, recycling, substitution, and dematerialization. In any event, sustainable development will soon return to the Earth's Critical Zone of life because Mother Nature—the ruling terrestrial economist—abhors long-term overdrafting of resources.
DS202010-1843
2020
Erofeeva, K.G., Samsonov, A.V., Stepanova, A.V., Larionova, Yu.O., Dubinina, E.O., Egorova, S.V., Arzamastesev, A.A., Kovalchuk, E.V., Abramova, V.D.Olivine and clinopyroxene phenocrysts as a proxy for the origin and crustal evolution of primary mantle melts: a case study of 2.40 Ga mafic sills in the Kola-Norwegian Terrane, northern Fennoscandia.Petrology, Vol. 28, 4, pp. 338-356. pdfEurope, Norway, Kola Peninsulamelting

Abstract: New petrographic, geochemical, and isotopic (Sr, Nd, and ?18?) data on olivine and pyroxene phenocrysts provide constraints on the composition and crustal evolution of primary melts of Paleoproterozoic (2.40 Ga) picrodoleritic sills in the northwest Kola province, Fennoscandian Shield. The picrodolerites form differentiated sills with S-shaped compositional profiles. Their chilled margins comprise porphyritic picrodolerite (upper margin) and olivine gabbronorite (bottom) with olivine and clinopyroxene phenocrysts. Analysis of the available data allows us to recognize three main stages in the crystallization of mineral assemblages. The central parts of large (up to 2 mm) olivine phenocrysts (Ol-1-C) crystallized at the early stage. This olivine (Mg# 85-92) is enriched in Ni (from 2845 to 3419 ppm), has stable Ni/Mg ratio, low Ti, Mn and Co concentrations, and contains tiny (up to 10 ?m) diopside-spinel dendritic lamella that probably originated due to the exsolution from high Ca- and Cr- primary magmatic olivine. All these features of Ol-1-C are typical of olivine from primitive picritic and komatiitic magmas (De Hoog et al., 2010; Asafov et al., 2018). Ol-1-C contains large (up to 0.25 mm) crystalline inclusions of high-Al enstatite (Mg# 80-88) and clinopyroxene (Mg# 82-90), occasionally in association with Ti-pargasite and chromian spinel (60.4 wt.% Al2O3). These inclusions are regarded as microxenoliths of wall rock that were captured by primary melt at depths more than 30 km and preserved due to the conservation in magmatic olivine. The second stage was responsible for the crystallization of Ol-1 rim (Ol-1-R), small (up to 0.3 mm) olivine (Ol-2, Mg# 76-85) grains, and central parts of large (up to 1.5 mm) clinopyroxene (Cpx-C) phenocrysts in the mid-crustal transitional magma chamber (at a depth of 15-20 km) at 1160-1350°C. At the third stage, Cpx-C phenocrysts were overgrown by low-Mg rims (Mg# 70-72) similar in composition to the groundmass clinopyroxene from chilled picrodolerite and gabbro-dolerite in the central parts of the sills. This stage likely completed the evolution of picrodoleritic magma and occurred in the upper crust at a depth of about 5 km. All stages of picrodoleritic magma crystallization were accompanied by contamination. Primary melts were contaminated by upper mantle and/or lower crust as recognized from xenocrystic inclusions in Ol-1-C. The second contamination stage is supported by the negative values of ?Nd(2.40) = -1.1 in clinopyroxene phenocrysts. At the third stage, contamination likely occurred in the upper crust when ascending melts filled gentle fractures. This caused vertical whole-rock Nd heterogeneity in the sills (Erofeeva et al., 2019), and difference in Nd isotopic composition of clinopyroxene phenocrysts and doleritic groundmass. It was also recognized that residual evolved melts are enriched in radiogenic strontium but have neodymium isotopic composition similar to other samples. It could be explained by the interaction of the melts with fluid formed via decomposition of biotite from surrounding gneisses under the effect of high-temperature melts.
DS202003-0336
2020
Ethier, B.Analyzing entangled territorialities and indigenous use of maps: Atikamekw Nehirowisiwok ( Quebec, Canada) dynamics of territorial negotiations, frictions, and creativity.The Canadian Geographer, https://doi.org/ 10.1111/cag.12603Canada, Quebeclegal

Abstract: This paper highlights the relevance of analyzing entangled territorialities and Indigenous use of maps in order to better understand what Lévy describes in terms of “spatial capital”—the socio?economic dynamics and power relationships maintained and negotiated between the stakeholders interacting within the Indigenous forestland. More specifically, it discusses the entanglement dynamics of land tenures coexisting today within Nitaskinan, the ancestral territory claimed by the Atikamekw Nehirowisiwok. Within Nitaskinan, members of the First Nation negotiate the continuity of their practices, occupation, and use of ancestral hunting territories with state institutions, logging companies, and non?Indigenous members of civil society who have interests in the land resources. All these stakeholders implement different territorial regimes that interact and sometimes conflict. Based on concrete ethnographic examples, the analysis presented here focuses on the compromises, frictions, resistance, and creativity that are part of territorial coexistence between Indigenous and non?Indigenous people. This paper is about the entanglement of Indigenous and state's land tenures in a Canadian context. The study highlights the relevance of analyzing entangled territorialities to better understand the power relationships within Indigenous forestland. The study demonstrates the complex articulations between domination and resistance dynamics in Indigenous mapping in a territorial negotiation process. This paper is about the entanglement of Indigenous and state's land tenures in a Canadian context. The study highlights the relevance of analyzing entangled territorialities to better understand the power relationships within Indigenous forestland. The study demonstrates the complex articulations between domination and resistance dynamics in Indigenous mapping in a territorial negotiation process.
DS202009-1627
2020
Fareeduddin, Pant, N.C., Gupta, S., Chakraborty, P., Sensarma, S., Jain, A.K., Prasad, G.V.R., Srivastava, P., Rajan, S., Tiwari, V.M.The geodynamic evolution of the Indian subcontinent - an introduction.Episodes, Vol. 43, 1, pp. 8p.Indiacarbonatites
DS202005-0730
2020
Fareeduddin., Pant, N.C., Gupta, S., Chakraborty, P., Sensarma, S., Jain, A.K., Prasad, G.V.R., Srivastava, P., Rjan, S., Tiwari, V.M.The geodynamic evolution of the Indian subcontinent - an introduction.Episodes ( IUGS), Vol. 43, 1, pp. 1-18.Indiacarbonatite
DS202004-0510
2020
Faryad, S.W., Cuthbert, S.J.High temperature overprint in (U)HPM rocks exhumed from subduction zones: a product of isothermal decompression or a consequence of slab break-off ( slab rollback?) Dabie Sulu, KokechtavEarth-Science Reviews, Vol. 202, 103108 14p. PdfChina, Russiasubduction

Abstract: This paper presents and discusses petrological observations from high- to ultrahigh-pressure (U)HP metamorphic terrains in relation to existing geophysical and numerical models for subduction and exhumation processes in orogenic belts. The interpretations are mostly based on observations from gneiss terrains bearing abundant bodies mafic (meta-)eclogite and ultramafic garnet peridotite and pyroxenite, exposed in collisional orogens. The inclusions and compositional zoning of minerals are considered to be first order information that is needed to constrain PT paths of HP-UHP rocks and reconstruct the related geodynamic models for subduction and exhumation of crustal and mantle rocks. The Bohemian Massif of the European Variscides is used as the basis for a model example to explain these processes, but (U)HP rocks from various other terrains are taken into consideration to discuss available PT paths in relation to proposed subduction and exhumation rates of (U)HP rocks based on geophysical and geochronological data. Primarily information used in this respect include textural relations and preserved prograde zoning in minerals from many (U)HP rocks, which reveal that a relatively cool geothermal gradient typical of subduction zones tended to prevail during the prograde and peak pressure segments of PT paths prior to initiation of exhumation and may have continued, even with cooling, if exhumation rates were rapid. The commonly applied interpretation of isothermal decompression during exhumation is critically appraised, considering whether a simple thermal relaxation (and radiogenic heating) during exhumation is responsible for formation of post-peak pressure, retrograde mineral assemblages and textures observed in (U)HP rocks. We go on to consider whether this can satisfactorily explain the often pervasive medium-pressure, high-temperature metamorphic re-equilibration of (U)HP rocks or whether an additional, external source of heat is a better explanation. We conclude that the commonly observed high-temperature metamorphic overprint exhibited by (U)HP rocks occurs mostly after rocks have been exhumed from the subduction channel and have reached normal crustal positions, when mantle upwelling resulting from slab breakoff (delamination) or slab rollback takes place at the onset of continent-continent collision. We also explore contrasting PT trajectories for mantle rocks that have been entrained into crustal material during their subduction or exhumation; PT paths of mantle and subducted crustal rocks tend to converge as mantle rocks impinge upon the cooler subduction zone and, once entrained, share a common evolution that depends on the exhumation mechanism and rate. Considering all of the data presented in this work we conclude that the diverse, polyphase metamorphic evolution exhibited by (U)HP terrains, embodied in the PT paths of HP and UHP rocks, has important consequences for reconstructing their changing thermal regimes and provides important constraints for geodynamic models involving subduction and the transition to collision.
DS202008-1389
2020
Fedortchouk, Y., Chinn, I.L.Crystallization conditions of kimberlite magma.Goldschmidt 2020, 1p. AbstractAfrica, Botswana, Canada, Northwest Territoriesdeposit - Orapa, Lac de Gras

Abstract: Experiments on diamond crystallization in kimberlite melt were performed for 40 h at 6.3 GPa in the temperature range of 1300-1570 °C and at 7.5 GPa in the temperature range of 1450-1570 °C, using a multianvil high-pressure apparatus of split-sphere type. Group I kimberlite from the Udachnaya-East pipe and a synthetic multicomponent mixture modeling the average composition of group II kimberlites were used as starting materials. The experiments have shown that diamond growth on seed crystals in the kimberlite melt in equilibrium with olivine, pyroxene, and garnet starts from 1400 °C at 7.5 GPa and from 1520 °C at 6.3 GPa. Diamond nucleation requires higher temperature and pressure, 1570 °C and 7.5 GPa. The alkali-enriched and silicate-depleted derivates of kimberlite melts ensure the growth and nucleation of diamond at lower P and T values: 1400 °C at 7.5 GPa and 1520 °C at 6.3 GPa. The results obtained evidence that temperature, pressure, and the composition of crystallization medium are the main factors controlling diamond formation processes in the kimberlite melts and their derivates.
DS202003-0337
2020
Feng, M., Song, W., Kynicky, J., Smith, M., Cox, C., Kotlanova, M., Brtnicky, M., Fu, W., Wei, C.Primary rare earth element enrichment in carbonatites: evidence from melt inclusions in Ulgii Khild carbonatite, Mongolia.Ore Geology Reviews, Vol. 117, 14p. PdfAsia, Mongoliadeposit - Ulgii Khild
DS202002-0183
2019
First, E.C., Leonhardi, T.C., Hammer, J.E.Effects of superheating magnitude on olivine growth.Contributions to Mineralogy and Petrology, Vol. 175, 13p. pdfMantlemagmatism

Abstract: Magmatic superheating is a condition with relevance to natural systems as well as experimental studies of crystallization kinetics. Magmas on Earth and other planetary bodies may become superheated during adiabatic ascent from the mantle or as a consequence of meteorite impact-generated crustal melting. Experimental studies of igneous processes commonly employ superheating in the homogenization of synthetic starting materials. We performed 1-atmosphere dynamic crystallization experiments to study the effects of superliquidus thermal history on the morphologies and compositions of subsequently grown olivine crystals. An ultramafic volcanic rock with abundant olivine was fused above the experimentally determined liquidus temperature (1395 °C), held for 0, 3, or 12 h, cooled at 25 °C h?1, and quenched from 200 °C below the liquidus, all at constant fO2, corresponding to FMQ-2?±?0.2 log units. An increase in olivine morphologic instability is correlated with superheating magnitude, parameterized as the integrated time the sample is held above the liquidus (“TtL”; °C h). We infer that a delay in nucleation, which intensifies monotonically with increasing TtL, causes crystal growth to be increasingly rapid. This result indicates that the structural relaxation time scale controlling the formation of crystal nuclei is (a) far longer than the time scale associated with viscous flow and (b) exceeds the liquidus dwell times typically imposed in crystallization experiments. The influence of magmatic superheating on crystal morphology is similar in sense and magnitude to that of subliquidus cooling rate and thus, both factors should be considered when interpreting the thermal history of a volcanic rock containing anhedral olivine.
DS202007-1140
2020
Fitzpayne, A., Giuliani, A., Hergt, J., Woodhead, J.D., Maas, R.Isotopic analyses of clinopyroxene demonstrate the effects of mantle metasomatism upon the lithospheric mantle.Lithos, in press available, 77p. PdfAfrica, South Africadeposit - Kimberley

Abstract: The trace element and radiogenic isotope systematics of clinopyroxene have frequently been used to characterise mantle metasomatic processes, because it is the main host of most lithophile elements in the lithospheric mantle. To further our understanding of mantle metasomatism, both solution-mode Sr-Nd-Hf-Pb and in situ trace element and Sr isotopic data have been acquired for clinopyroxene grains from a suite of peridotite (lherzolites and wehrlites), MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside), and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks from the Kimberley kimberlites (South Africa). The studied mantle samples can be divided into two groups on the basis of their clinopyroxene trace element compositions, and this subdivision is reinforced by their isotopic ratios. Type 1 clinopyroxene, which comprises PIC, wehrlite, and some sheared lherzolite samples, is characterised by low Sr (~100-200 ppm) and LREE concentrations, moderate HFSE contents (e.g., ~40-75 ppm Zr; La/Zr < 0.04), and restricted isotopic compositions (e.g., 87Sr/86Sri = 0.70369-0.70383; ?Ndi = +3.1 to +3.6) resembling those of their host kimberlite magmas. Available trace element partition coefficients can be used to show that Type 1 clinopyroxenes are close to being in equilibrium with kimberlite melt compositions, supporting a genetic link between kimberlites and these metasomatised lithologies. Thermobarometric estimates for Type 1 samples in this study indicate equilibration depths of 135-160 km within the lithosphere, thus showing that kimberlite melt metasomatism is prevalent in the deeper part of the lithosphere beneath Kimberley. In contrast, Type 2 clinopyroxenes occur in MARID rocks and coarse granular lherzolites in this study, which derive from shallower depths (<135 km), and have higher Sr (~350-1000 ppm) and LREE contents, corresponding to higher La/Zr of > ~ 0.05. The isotopic compositions of Type 2 clinopyroxenes are more variable and extend from compositions resembling the “enriched mantle” towards those of Type 1 rocks (e.g., ?Ndi = ?12.7 to ?4.4). To constrain the source of these variations, in situ Sr isotope analyses of clinopyroxene were undertaken, including zoned grains in Type 2 samples. MARID and lherzolite clinopyroxene cores display generally radiogenic but variable 87Sr/86Sri values (0.70526-0.71177), which are correlated with Sr contents and La/Zr ratios, and which might be explained by the interaction between peridotite and melts from different enriched sources within the lithospheric mantle. Most notably, the rims of these Type 2 clinopyroxenes trend towards compositions similar to those of the host kimberlite and Type 1 clinopyroxene from PIC and wehrlites. These results are interpreted to represent clinopyroxene overgrowth during late-stage (shortly before/during entrainment) metasomatism by kimberlite magmas. Our study shows that a pervasive, alkaline metasomatic event caused MARID to be generated and harzburgites to be converted to lherzolite in the lithospheric mantle beneath the Kimberley area, which was followed by kimberlite metasomatism during Cretaceous magmatism. This latter event is the time at which discrete PIC, wehrlite, and sheared lherzolite lithologies were formed, and MARID and granular lherzolites were partly modified.
DS202007-1141
2020
Fitzpayne, A., Prytulak, J., Giuliani, A., Hergt, J.Thallium content and isotopic composition of phlogopite in mantle derived MARID and PIC rocks.Chemical Geology, Vol. 531, 119347Mantlegeochronology
DS202008-1390
2020
Fitzpaynek, A., Giuliani, A., Magalhaes, N., Soltys, A., Fiorentini, M., Farquhar, J.The petrology and sulphur istopic composition of sulphide and sulphate in the Kimberley kimberlites.Goldschmidt 2020, 1p. AbstractAfrica, South Africadeposit - Kimberley

Abstract: The petrology and bulk-rock sulphur isotopic compositions of kimberlite samples from four localities (Bultfontein, De Beers, Kimberley, Wesselton) of the archetypal Kimberley cluster, South Africa, were used to investigate the origin(s) of S in kimberlites and gain insights into the occurrence of recycled crustal material in the source of Mesozoic kimberlites. The samples, which show variable degrees of alteration, are all hypabyssal and were derived from coherent root-zones as well as dykes and sills. Typical sulphide minerals are Cu-Fe-Ni-sulphides with less common pyrite, galena, sphalerite, and djerfisherite. They occur in a variety of textural associations, for example as groundmass phases, secondary inclusions in olivine, inclusions in matrix phases (e.g., phlogopite), or in carbonate-serpentine segregations. Barite is the most commonly observed sulphate phase. Bulk-sample ?34SVCDT values of sulphides in fresh kimberlites, which mostly do not contain barite, vary from - 2.0 to -5.7 ‰. Slightly altered kimberlite samples, in which sulphides were generally associated with serpentine, returned somewhat higher bulk-sulphide ?34SVCDT (-3.8 to +1.1 ‰). One sample from the Wesselton Water Tunnel Sills complex contains abundant barite and pyrite in its groundmass, with the latter having ?34SVCDT (+0.2 to +1.9 ‰) similar to altered kimberlites. Two further altered samples returned ?34SVCDT values (-10.1 to -13.0 ‰) that suggest a contribution from the local country rocks (Dwyka shale: ?34SVCDT from -10.2 to -10.5 ‰). All samples have near-zero ?33S values, suggesting that material displaying mass-independent fractionation has not played an important role. The negative ?34SVCDT values of fresh kimberlites from Kimberley suggest the involvement of recycled crustal material in their source, which is consistent with radiogenic isotope compositions. Overall, it appears that most kimberlitic sulphide S isotopic compositions can be explained by the action of a few typical magmatic/hydrothermal processes.
DS202012-2214
2009
Flament, N.Secular cooling of the solid Earth, emergence of the continents , and evolution of Earth's external envelopes.Thesis, Phd Univ. Sydney *** NOTE DATE, 210p. PdfMantlecratons

Abstract: The secular cooling of the mantle and of the continental lithosphere trigger an increase in the area of emerged land. The corollary increase in weathering and erosion processes has major consequences for the evolution of Earth's external envelopes. We developed a physical model to evaluate the area of emerged land as a function of mantle temperature, continental area, and of the distribution of continental elevations. Our numerical results show that less than 15% of Earth's surface consisted of emerged land by the end of the Archaean. This is consistent with many geological and geochemical observations. To estimate the secular cooling of the continental lithosphere, we combined thermo-mechanical models with fi eld observations. Our results, constrained by geological data, suggest that the Moho temperature has decreased by ~ 200ºC over 2.7 Ga in the Pilbara Craton. To evaluate the eff ect of continental growth on the evolution of the area of emerged land, we developed a model based on published thermal evolution models. Our results suggest that the area of emerged land was less than 5% of Earth's surface in the Archaean, and that it does not depend on crustal growth. This allows to reconcile the evolution of oceanic 87Sr/86Sr with early crustal growth models. Continents are enriched in phosphorus, which is essential to the biosphere. The emergence of the continents would thus have triggered an increase in the production of oxygen by photosynthetic micro-organisms, possibly contributing to the oxidation of the atmosphere 2.4 Ga ago.
DS202006-0919
2020
Flowers, R.M., Macdonald, F.A., Siddoway, C.S., Havranek, R.Diachronous development of Great Unconformities before Neoproterozoic Snowlball Earth. Proceedinds of the National Academy of Sciences, Vol. 117, 19, 9p. PdfUnited States, Coloradogeothermometry

Abstract: The Great Unconformity marks a major gap in the continental geological record, separating Precambrian basement from Phanerozoic sedimentary rocks. However, the timing, magnitude, spatial heterogeneity, and causes of the erosional event(s) and/or depositional hiatus that lead to its development are unknown. We present field relationships from the 1.07-Ga Pikes Peak batholith in Colorado that constrain the position of Cryogenian and Cambrian paleosurfaces below the Great Unconformity. Tavakaiv sandstone injectites with an age of ?676 ± 26 Ma cut Pikes Peak granite. Injection of quartzose sediment in bulbous bodies indicates near-surface conditions during emplacement. Fractured, weathered wall rock around Tavakaiv bodies and intensely altered basement fragments within unweathered injectites imply still earlier regolith development. These observations provide evidence that the granite was exhumed and resided at the surface prior to sand injection, likely before the 717-Ma Sturtian glaciation for the climate appropriate for regolith formation over an extensive region of the paleolandscape. The 510-Ma Sawatch sandstone directly overlies Tavakaiv-injected Pikes granite and drapes over core stones in Pikes regolith, consistent with limited erosion between 717 and 510 Ma. Zircon (U-Th)/He dates for basement below the Great Unconformity are 975 to 46 Ma and are consistent with exhumation by 717 Ma. Our results provide evidence that most erosion below the Great Unconformity in Colorado occurred before the first Neoproterozoic Snowball Earth and therefore cannot be a product of glacial erosion. We propose that multiple Great Unconformities developed diachronously and represent regional tectonic features rather than a synchronous global phenomenon.
DS202008-1391
2019
Fofana, M., Steyn, T.Monitoring the performance of DMS circuits using RhoVol technology. ( DMC)The Journal of the Southern African Insitute of Mining and Metallurgy, Vol. 119, Feb. 6p. PdfAfrica, South AfricaDMC

Abstract: The petrology and bulk-rock sulphur isotopic compositions of kimberlite samples from four localities (Bultfontein, De Beers, Kimberley, Wesselton) of the archetypal Kimberley cluster, South Africa, were used to investigate the origin(s) of S in kimberlites and gain insights into the occurrence of recycled crustal material in the source of Mesozoic kimberlites. The samples, which show variable degrees of alteration, are all hypabyssal and were derived from coherent root-zones as well as dykes and sills. Typical sulphide minerals are Cu-Fe-Ni-sulphides with less common pyrite, galena, sphalerite, and djerfisherite. They occur in a variety of textural associations, for example as groundmass phases, secondary inclusions in olivine, inclusions in matrix phases (e.g., phlogopite), or in carbonate-serpentine segregations. Barite is the most commonly observed sulphate phase. Bulk-sample ?34SVCDT values of sulphides in fresh kimberlites, which mostly do not contain barite, vary from - 2.0 to -5.7 ‰. Slightly altered kimberlite samples, in which sulphides were generally associated with serpentine, returned somewhat higher bulk-sulphide ?34SVCDT (-3.8 to +1.1 ‰). One sample from the Wesselton Water Tunnel Sills complex contains abundant barite and pyrite in its groundmass, with the latter having ?34SVCDT (+0.2 to +1.9 ‰) similar to altered kimberlites. Two further altered samples returned ?34SVCDT values (-10.1 to -13.0 ‰) that suggest a contribution from the local country rocks (Dwyka shale: ?34SVCDT from -10.2 to -10.5 ‰). All samples have near-zero ?33S values, suggesting that material displaying mass-independent fractionation has not played an important role. The negative ?34SVCDT values of fresh kimberlites from Kimberley suggest the involvement of recycled crustal material in their source, which is consistent with radiogenic isotope compositions. Overall, it appears that most kimberlitic sulphide S isotopic compositions can be explained by the action of a few typical magmatic/hydrothermal processes. One of the most important performance indicators of a dense medium cyclone (DMC) circuit is the Tromp curve, and by extension the separation density and Ecart Probable (Ep) values. The densimetric profiles of DMC product streams have been traditionally acquired using heavy liquid sinkfloat analysis, which has certain disadvantages, such as the associated safety and health risks. More recently, non-toxic media such as lithium hetero-polytungstates (LST) have been used, with the desired densities being achieved by maintaining the solutions at specific temperatures. However, the high costs of these liquids can be prohibitive. The long turnaround time of the sink-float analysis is a further disadvantage for timeous interventions to the operating set-points of the DMC process. The RhoVol technology can generate the density distribution of a batch of particles in a rapid, accurate, repeatable, and safe manner. Additional data of interest, such as particle size and shape, are also measured and reported on a per-particle basis. Furthermore, samples can be sorted into discrete sorting bins based on any of the measured parameters of the particle, making further analyses of the material possible. This technology has applications across all commodities that use the DMC, particularly in the size fractions 25 +8 mm and 8 +3 mm. To date, laboratory results have proved very encouraging separation densities are within 5% of traditional sink-float results, and the technology is being introduced to diamond DMC plants.
DS202002-0184
2019
Forster, M.W.Subduction zone metasomatism and its consequences for potassium rich magmatism and deep nitrogen recycling.Thesis Phd .Macquarie University, 250p. PdfMantlemetasomatism

Abstract: In total, subduction zones span 40,000 km across Earth’s surface and recycle an average thickness of 500 m of sediment. During burial and heating these sediments eventually start melting at T >675 °C, following which Si-rich hydrous melts infiltrate the peridotites of the mantle wedge above the subducting slab. In this thesis, a high-pressure experimental approach is used to examine the reaction of sediments and peridotites at 2-6 GPa in subduction zones and its consequences on the generation of K-rich magmatism and on deep nitrogen cycling. All experiments are conducted in a layered arrangement, where the depleted peridotite is placed above the sediments in a 1:1 ratio. At 2-3 GPa, the reaction of melts of sediment with depleted peridotite, simulating the fore-arc of a subduction zone, leads to the formation of layered phlogopite pyroxenites and selective incorporation of major and trace elements in these metasomatic layers. Partial melting of these phlogopite pyroxenites produces melts rich in K2O (>9 wt%) with K/Na >>2 and a trace element pattern comparable to “orogenic lamproites”. At similar pressures, the reaction of hydrous mantle melts with depleted peridotites produces metasomatic layers that show K/Na ~1 and a trace element pattern that closely resembles “anorogenic lamproites”. In both cases, K-enrichment is facilitated by the crystallization of an eclogitic residue rich in Na, poor in K, and consequently with low K/Na. At 4-6 GPa, the reaction of melts of sediment with depleted peridotite is does not produce mica, instead resulting in alkali chlorides with K/Na ratios similar to saline fluid inclusions in diamonds. Besides the chlorides, magnesite also crystallises in the peridotite. Both phases are important ingredients for the generation of salty kimberlites such as Udachnaya East. The change in metasomatic style from mica- to chloride formation between 3 to 4 GPa corresponds to the depth of the mid-lithospheric discontinuity, a zone of low seismic velocities that is found intermittently beneath all continents at a depth of 80-100 km. The subduction of sediment is the main mechanism that recycles nitrogen back to Earth’s mantle. The partitioning of nitrogen between fluid and melt (DN(Fluid/Melt)) and fluid and bulk residue (melt+mica) (DN(Fluid/Bulk)) was found to increase linearly with temperature normalized to pressure. Using the new partition coefficients, the amount of N recycled to Earth’s mantle since the onset of subduction is calculated as 50 ±6 %.
DS202002-0185
2020
Forster, M.W., Buhre, S., Xu, B., Prelevic, D., Mertz-Kraus, R., Foley, S.F.Two stage origin of K-enrichment in ultrapotassic magmatism simulated by melting of experimentally metasomatized mantle.MDPI Minerals, Vol. 10, 41;doe.10.3390/min10010041 21p. PdfMantlemetasomatism

Abstract: The generation of strongly potassic melts in the mantle requires the presence of phlogopite in the melting assemblage, while isotopic and trace element analyses of ultrapotassic rocks frequently indicate the involvement of subducted crustal lithologies in the source. However, phlogopite-free experiments that focus on melting of sedimentary rocks and subsequent hybridization with mantle rocks at pressures of 1-3 GPa have not successfully produced melts with K2O >5 wt%-6 wt%, while ultrapotassic igneous rocks reach up to 12 wt% K2O. Accordingly, a two-stage process that enriches K2O and increases K/Na in intermediary assemblages in the source prior to ultrapotassic magmatism seems likely. Here, we simulate this two-stage formation of ultrapotassic magmas using an experimental approach that involves re-melting of parts of an experimental product in a second experiment. In the first stage, reaction experiments containing layered sediment and dunite produced a modally metasomatized reaction zone at the border of a depleted peridotite. For the second-stage experiment, the metasomatized dunite was separated from the residue of the sedimentary rock and transferred to a smaller capsule, and melts were produced with 8 wt%-8.5 wt% K2O and K/Na of 6-7. This is the first time that extremely K-enriched ultrapotassic melts have been generated experimentally from sediments at low pressure applicable to a post-collisional setting.
DS202006-0920
2020
Foster, A., Darbyshire, F., Schaeffer, A.Anisotropic structure of the central North American craton surrounding the Mid-continent rift: evidence form Rayleigh waves.Precambrian Research, Vol. 342, 18p. PdfUnited States, Canadageophysics - seismics
DS202004-0511
2020
Fosu, B.R., Ghosh, P., Viladkar, S.G.Clumped isotope geochemistry of carbonatites in the north-western Deccan igneous province: aspects of evolution, post-depositional alteration and mineralization.Geochimica et Cosmochimica Acta, Vol. 274, pp. 118-135.Indiacarbonatite

Abstract: Carbonatites crystallise along a wide range of solidus temperatures and are commonly affected by post-magmatic textural re-equilibration and diagenesis. Further insights into the formation and modification of carbonatites are provided using carbon, oxygen and clumped isotope (?47) data of rocks from spatially associated Amba Dongar and Siriwasan alkaline complexes in the north-western Deccan igneous province, India. We derive apparent equilibrium blocking temperatures to help constrain the thermal evolution of the different rock types found within the alkaline complexes in a petrographic context. The apparent temperatures for the carbonatites are significantly low but are consistent with reports on other global carbonatites and model predictions. Rapidly cooled Oldoinyo Lengai natrocarbonatite yielded similar low temperatures, even in the absence of bulk isotopic alteration. The isotopic proxies and petrographic observations favour both isotopic exchange reactions and diagenesis in altering ?47 values in calciocarbonatites. Diagenetic reactions are however strongly favoured, as secondary calcites in nephelinites and ferrocarbonatites record much lower temperatures than in the calciocarbonatites, highlighting the effect of fluids and diagenetic reactions in 13C18O bond ordering in carbonatites. Variations in the CO isotope data reveal the coupling of fractional crystallisation and post-magmatic fluid-rock interactions on bulk rock composition. After emplacement, the resetting of clumped isotope signatures in carbonatites is facilitated by post-magmatic processes in both open and closed systems.
DS202003-0338
2020
Franz, G., Vyshnevsky, O., Taran, M., Khomenko, V., Wiedenbeck, M., Schiperski, F., Nissen, J.A new emerald occurrence from Kruta Balka, western Peri-Azovian, Ukraine: implications for understanding the crystal chemistry of emerald.American Mineralogist, Vol. 105, pp. 162-181. pdfEurope, Ukraineemerald

Abstract: We investigated emerald, the bright-green gem variety of beryl, from a new locality at Kruta Balka, Ukraine, and compare its chemical characteristics with those of emeralds from selected occurrences worldwide (Austria, Australia, Colombia, South Africa, Russia) to clarify the types and amounts of substitutions as well as the factors controlling such substitutions. For selected crystals, Be and Li were determined by secondary ion mass spectrometry, which showed that the generally assumed value of 3 Be atoms per formula unit (apfu) is valid; only some samples such as the emerald from Kruta Balka deviate from this value (2.944 Be apfu). An important substitution in emerald (expressed as an exchange vector with the additive component Al2Be3Si6O18) is (Mg,Fe2+)NaAl1?1, leading to a hypothetical end-member NaAl(Mg,Fe2+)[Be3Si6O18] called femag-beryl with Na occupying a vacancy position (?) in the structural channels of beryl. Based on both our results and data from the literature, emeralds worldwide can be characterized based on the amount of femag-substitution. Other minor substitutions in Li-bearing emerald include the exchange vectors LiNa2Al1?2 and LiNaBe1?1, where the former is unique to the Kruta Balka emeralds. Rarely, some Li can also be situated at a channel site, based on stoichiometric considerations. Both Cr- and V-distribution can be very heterogeneous in individual crystals, as shown in the samples from Kruta Balka, Madagascar, and Zimbabwe. Nevertheless, taking average values available for emerald occurrences, the Cr/(Cr+V) ratio (Cr#) in combination with the Mg/(Mg+Fe) ratio (Mg#) and the amount of femag-substitution allows emerald occurrences to be characterized. The "ultramafic" schist-type emeralds with high Cr# and Mg# come from occur-rences where the Fe-Mg-Cr-V component is controlled by the presence of ultramafic meta-igneous rocks. Emeralds with highly variable Mg# come from "sedimentary" localities, where the Fe-Mg-Cr-V component is controlled by metamorphosed sediments such as black shales and carbonates. A "transitional" group has both metasediments and ultramafic rocks as country rocks. Most "ultramafic" schist type occurrences are characterized by a high amount of femag-component, whereas those from the "sedimentary" and "transitional" groups have low femag contents. Growth conditions derived from the zoning pattern combined replacement, sector, and oscillatory zoning in the Kruta Balka emeralds indicate disequilibrium growth from a fluid along with late-stage Na-infiltration. Inclusions in Kruta Balka emeralds (zircon with up to 11 wt% Hf, tourmaline, albite, Sc-bearing apatite) point to a pegmatitic origin.
DS202001-0011
2019
Frezzotti, M.L.Diamond growth from organic compounds in hydrous fluids deep within the Earth.Nature Communications, doi.org/10.1038/ s41467-019-12984-y 8p. PdfMantlesubduction

Abstract: At subduction zones, most diamonds form by carbon saturation in hydrous fluids released from lithospheric plates on equilibration with mantle rocks. Although organic molecules are predicted among dissolved species which are the source for carbon in diamonds, their occurrence is not demonstrated in nature, and the physical model for crustal diamond formation is debated. Here, using Raman microspectroscopy, I determine the structure of carbon-based phases inside fluid inclusions in diamond-bearing rocks from the Alps. The results provide direct evidence that diamond surfaces are coated by sp2-, and sp3-bonded amorphous carbon and functional groups of carboxylic acids (e.g., carboxyl, carboxylate, methyl, and methylene), indicating the geosynthesis of organic compounds in deep hydrous fluids. Moreover, this study suggests diamond nucleation via metastable molecular precursors. As a possible scenario, with carbon saturation by reduction of carboxylate groups, I consider tetrahedral H-terminated C groups as templates for the growth of sp3-structured carbon.
DS202008-1392
2020
Frezzotti, M.L.Diamond growth from organic compounds in hydrous fluids deep within the Earth.Goldschmidt 2020, 1p. AbstractMantlesubduction

Abstract: Subduction diamonds represent the sequestration of carbon from fluids released from lithospheric plates at mantle depths. In deep fluids, besides reactive molecular species (e.g., CO2), inorganic, and organic aqueous ionic species have been proposed as a source of carbon in diamonds (Sverjensky et al., 2014). Unequivocal signatures of organic species, however, have not been found, neither a unified model for diamond nucleation and growth has been proposed. Here, I use Raman microspectroscopy to determine the structure and composition of carbon-based phases precipitated inside diamond-bearing fluid inclusions in metamorphic rocks from the Alps to reveal the spontaneous products on carbon saturation in deep Earth’s aqueous fluids. I find that microand nano-sized diamonds are coated by sp2-, and sp3-bonded amorphous carbon that shows Raman modes of attached organic functional group structures (e.g., carboxyl, carboxylate, methyl, and methylene). Present data suggest that decomposition of complex carboxylic acids can induce diamond nucleation on the reduction of the carboxyl groups, whereas sp3-bonded radicals can create structural intermediates allowing diamond growth (Frezzotti, 2019). This formation mechanism is consistent with nucleation models via metastable molecular precursors (Gebbie et al., 2018). The present study provides direct evidence that, deep within the Earth, dissolved inorganic carbon can spontaneously evolve to organic species in the absence of biologically catalyzed processes. Results suggest that the Earth’s interior should be considered as a favorable environment for the origin of prebiotic organic compounds.
DS202004-0512
2020
Gales, E., Black, B., Elkins-Tanton, E.Carbonatites as a record of the carbon isotope composition of large igneous province outgassing.Earth and Planetary Science Letters, Vol. 535, 116076 11p. PdfRussia, Siberiacarbonatite

Abstract: Large igneous province (LIP) eruptions have been linked in some cases to major perturbations of Earth's carbon cycle. However, few observations directly constrain the isotopic composition of carbon released by LIP magmas because carbon isotopes fractionate during degassing, which hampers understanding of the relative roles of mantle versus crustal carbon reservoirs. Carbonatite magmatism associated with LIPs provides a unique window into the isotopic systematics of LIP carbon because the majority of carbon in carbonatites crystalizes rather than degassing. Although the volume of such carbonatites is small, they offer one of the few available constraints on the mantle carbon originally hosted in other more voluminous magma types. Here, we present new data for the Guli carbonatites in the Siberian Traps. In addition, we compile ?260 published measurements of from carbonatites related to the Deccan Traps and the Paraná-Etendeka. We find no evidence for magmas with carbon isotope ratios lighter than depleted mantle values of ‰ from any of these LIPs, though some carbonatites range to heavier . We attribute relatively heavy in some carbonatites to either slightly 13C-enriched domains in the mantle lithosphere or carbon isotope fractionation in deep, carbon-saturated LIP magma reservoirs. The absence of a light component in LIP magmas supports the view that lithospheric carbon reservoirs must be tapped during cases of LIP magmatism linked with sharp negative carbon isotope excursions and mass extinctions.
DS202005-0731
2020
Galimov, E.M., Kaminsky, F.V., Shilobreeva, S.N., Sevastyanov, V.S., Voropaev, S.A., Khachatryan, G.K., Wirth, R., Schreiber, A., Saraykin, V.V., Karpov, G.A., Anikin, L.P.Enigmatic diamonds from the Tolbachik volcano, Kamchatka.American Mineralogist, Vol. 105, pp. 498-509. pdfRussiadeposit - Tolbachik

Abstract: Approximately 700 diamond crystals were identified in volcanic (mainly pyroclastic) rocks of the Tolbachik volcano, Kamchatka, Russia. They were studied with the use of SIMS, scanning and transmission electron microscopy, and utilization of electron energy loss spectroscopy and electron diffraction. Diamonds have cube-octahedral shape and extremely homogeneous internal structure. Two groups of impurity elements are distinguished by their distribution within the diamond. First group, N and H, the most common structural impurities in diamond, are distributed homogeneously. All other elements observed (Cl, F, O, S, Si, Al, Ca, and K) form local concentrations, implying the existence of inclusions, causing high concentrations of these elements. Most elements have concentrations 3-4 orders of magnitude less than chondritic values. Besides N and H, Si, F, Cl, and Na are relatively enriched because they are concentrated in micro- and nanoinclusions in diamond. Mineral inclusions in the studied diamonds are 70-450 nm in size, round- or oval-shaped. They are represented by two mineral groups: Mn-Ni alloys and silicides, with a wide range of concentrations for each group. Alloys vary in stoichiometry from MnNi to Mn2Ni, with a minor admixture of Si from 0 to 5.20-5.60 at%. Silicides, usually coexisting with alloys, vary in composition from (Mn,Ni)4Si to (Mn,Ni)5Si2 and Mn5Si2, and further to MnSi, forming pure Mn-silicides. Mineral inclusions have nanometer-sized bubbles that contain a fluid or a gas phase (F and O). Carbon isotopic compositions in diamonds vary from -21 to -29‰ ?13CVPDB (avg. = -25.4). Nitrogen isotopic compositions in diamond from Tolbachik volcano are from -2.32 to -2.58‰ ?15NAir. Geological, geochemical, and mineralogical data confirm the natural origin of studied Tolbachik diamonds from volcanic gases during the explosive stage of the eruption.
DS202009-1628
2018
Garber, J.M., Maurya, S., Hernandez, J.A., Duncan, M.S., Zeng, L., Zhang, H.L.Multidisciplenary constraints on the abundance of diamond and eclogite in the cratonic lithosphere.Geochemistry, Geophysics, Geosystems, Vol. 19: https://doi.org/10.1029/2018GC007534Mantleeclogite

Abstract: Some seismic models derived from tomographic studies indicate elevated shear?wave velocities (?4.7 km/s) around 120-150 km depth in cratonic lithospheric mantle. These velocities are higher than those of cratonic peridotites, even assuming a cold cratonic geotherm (i.e., 35 mW/m2 surface heat flux) and accounting for compositional heterogeneity in cratonic peridotite xenoliths and the effects of anelasticity. We reviewed various geophysical and petrologic constraints on the nature of cratonic roots (seismic velocities, lithology/mineralogy, electrical conductivity, and gravity) and explored a range of permissible rock and mineral assemblages that can explain the high seismic velocities. These constraints suggest that diamond and eclogite are the most likely high?Vs candidates to explain the observed velocities, but matching the high shear?wave velocities requires either a large proportion of eclogite (>50 vol.%) or the presence of up to 3 vol.% diamond, with the exact values depending on peridotite and eclogite compositions and the geotherm. Both of these estimates are higher than predicted by observations made on natural samples from kimberlites. However, a combination of ?20 vol.% eclogite and ~2 vol.% diamond may account for high shear?wave velocities, in proportions consistent with multiple geophysical observables, data from natural samples, and within mass balance constraints for global carbon. Our results further show that cratonic thermal structure need not be significantly cooler than determined from xenolith thermobarometry.
DS202002-0186
2020
Garcia, L.F., Abel, M., Perrin, M., dos Santis Alvarenga, R.The GeoCore ontology: a core ontology for general use in geology.Computers and Geosciences, Vol. 135, 104387 9p. PdfGlobalGeoCore

Abstract: Domain ontologies assume the role of representing, in a formal way, a consensual knowledge of a community over a domain. This task is especially difficult in a wide domain like Geology, which is composed of diversified science resting on a large variety of conceptual models that were developed over time. The meaning of the concepts used by the various professionals often depends on the particular vision that they have of a domain according to their background and working habits. Ontology development in Geology thus necessitates a drastic elucidation of the concepts and vocabulary used by geologists. This article intends to contribute to solving these difficulties by proposing a core ontology named GeoCore Ontology resting on the BFO top ontology, specially designed for describing scientific fields. GeoCore Ontology contains well-founded definitions of a limited set of general concepts within the Geology field that are currently considered by all geologists whatever their skill. It allows modelers to separately consider a geological object, the substance that constitutes it, the boundaries that limit it and the internal arrangement of the matter inside it. The core ontology also allows the description of the existentially dependent qualities attached to a geological object and the geological process that generated it in a particular geological age. This small set of formally defined and described concepts combined with concepts from BFO provides a backbone for deriving by subsumption more specialized geological concepts and also constitutes a baseline for integrating different existent domain ontologies within the Geology domain. The GeoCore ontology and the methodology that we used for building it, provide solutions for unveiling major misunderstanding regarding the concepts that are commonly used for formulating geological interpretations. This will facilitate the communication of this information to external Geology users and its integration in domain applications.
DS202002-0187
2020
Gardiner, N.J., Kirkland, C.L., Hollis, J.A., Cawood, P.A., Nebel, O., Szilas, K., Yakymchuk, C.North Atlantic craton architecture revealed by kimberlite-hosted crustal zircons.Earth and Planetary Science Letters, Vol. 534, 8p. PdfEurope, Greenlandkimberlite genesis

Abstract: Archean cratons are composites of terranes formed at different times, juxtaposed during craton assembly. Cratons are underpinned by a deep lithospheric root, and models for the development of this cratonic lithosphere include both vertical and horizontal accretion. How different Archean terranes at the surface are reflected vertically within the lithosphere, which might inform on modes of formation, is poorly constrained. Kimberlites, which originate from significant depths within the upper mantle, sample cratonic interiors. The North Atlantic Craton, West Greenland, comprises Eoarchean and Mesoarchean gneiss terranes - the latter including the Akia Terrane - assembled during the late Archean. We report U-Pb and Hf isotopic, and trace element, data measured in zircon xenocrysts from a Neoproterozoic (557 Ma) kimberlite which intruded the Mesoarchean Akia Terrane. The zircon trace element profiles suggest they crystallized from evolved magmas, and their Eo-to Neoarchean U-Pb ages match the surrounding gneiss terranes, and highlight that magmatism was episodic. Zircon Hf isotope values lie within two crustal evolution trends: a Mesoarchean trend and an Eoarchean trend. The Eoarchean trend is anchored on 3.8 Ga orthogneiss, and includes 3.6-3.5 Ga, 2.7 and 2.5-2.4 Ga aged zircons. The Mesoarchean Akia Terrane may have been built upon mafic crust, in which case all zircons whose Hf isotopes lie within the Eoarchean trend were derived from the surrounding Eoarchean gneiss terranes, emplaced under the Akia Terrane after ca. 2.97 or 2.7 Ga, perhaps during late Archean terrane assembly. Kimberlite-hosted peridotite rhenium depletion model ages suggest a late Archean stabilization for the lithospheric mantle. The zircon data support a model of lithospheric growth via tectonic stacking for the North Atlantic Craton.
DS202004-0513
2020
Gaucher, E.C.New perspectives in the industrial exploration for native hydrogen.Elements, Vol. pp. 8-9.Globalhydrogen

Abstract: Hydrogen gas (H2), when combusted, produces heat and water. There is no pollution, just water vapor. When hydrogen combines with oxygen, there is no generation of carbon dioxide, no production of cyclic hydro-carbons, no sulfur oxides (SOx), no nitrogen oxides (NOx), no ozone cogeneration. It seems that hydrogen, along with efficient energy production, solves many of our pollution problems, from urban air pollution to global warming. In the so-called Hydrogen Age of the future (Holland and Provenzano 2007), H2 will be mainly produced by the electrolysis of water using electricity that itself is derived from renewable energy sources or nuclear power plants. Steam methane reforming (a catalyzed reaction at high temperature where CH4 is combined with water to produce CO2 and H2) will only be acceptable as a source of H2 if it is associated with low-cost CO2 storage. But, in this future energy landscape, what is the role of naturally occurring hydrogen, sometimes referred to as native hydrogen?
DS202005-0732
2020
Gaucher, E.C.New perspectives in the industrial exploration for native hydrogen. ( brief review) whole issue on hydrogenElements, Vol. 18, 1, pp. 8-9.Globalhydrogen

Abstract: This article is a broad summary of the current state of knowledge concerning the potential exploration for native hydrogen across the globe. Native hydrogen has been identified in numerous source rocks in zones beyond sedimentary basins where petroleum companies typically operate. At the beginning of 2019 we may be at a tipping point with the first exploitable H2 field, potentially discovered in Mali. Of course, a number of issues and questions must still be resolved if these initial discoveries are to be transformed into a sustainable and abundant source of energy for society. However, the competencies that exist in the petroleum industry can readily be adapted by and to this new sector. New expertise will be needed to account for the reactivity of the hydrogen molecule in order to maximize exploration efforts and minimize the potential for chemical or biological consumption.
DS202012-2215
2020
Gautheron, C., Zeitler, P.K.Noble gases deliver cool dates from hot rocks. Elements, Vol. 16, pp. 303-309.MantleThermochronology

Abstract: Heat transfer in the solid Earth drives processes that modify temperatures, leaving behind a clear signature that we can measure using noble gas thermochronology. This allows us to record the thermal histories of rocks and obtain the timing, rate, and magnitude of phenomena such as erosion, deformation, and fluid flow. This is done by measuring the net balance between the accumulation of noble gas atoms from radioactive decay and their loss by temperature-activated diffusion in mineral grains. Together with knowledge about noble gas diffusion in common minerals, we can then use inverse models of this accumulation-diffusion balance to recover thermal histories. This approach is now a mainstream method by which to study geodynamics and Earth evolution.
DS202001-0012
2019
Gauthier, M.S., Hodder, T., Ross, M., Kelley, S.E. Rochester, A., McCausland< P. The subglacial mosaic of the Laurentide ice sheet; a study of the interior region of southwestern Hudson Bay.Quaternary Science Reviews, Vol. 214, pp. 1-27.Canada, Manitobageomorphology

Abstract: Reconstructions of past ice-flow provide useful insights into the long-term behaviour of past ice sheets and help to understand how glaciated landscapes are shaped. Here, we present reconstruction of a 10-phase ice-flow history from southwestern Hudson Bay in northeastern Manitoba (Canada), a dynamic region situated between two major ice dispersal centres of the Laurentide Ice Sheet. We utilize a diverse geologic dataset including 1900 field-based erosional indicators, 12 streamlined-landform flowsets, esker and meltwater corridor orientations, 103 till-fabrics analyses, and 1344 till-clast lithology counts. Our reconstruction suggests that both pre-MIS 2 and MIS 2 glaciations followed similar growth patterns, where ice advanced into study area from ice centered to the east (probably in northern Quebec), followed by a switch in ice-flow direction indicating flow from the Keewatin ice centre to the northwest and north. The cause for this switch in ice-flow orientation is uncertain, but the youngest switch may relate to retreat of ice during MIS 3 that then left space for Keewatin-sourced ice to advance over the study area. While modelling experiments indicate widespread cold-based conditions in the study area during the last glacial cycle, uniformly relict landscapes are not common. Instead, the glaciated landscape is palimpsest and commonly fragmented, forming a subglacial bed mosaic of erosional and depositional assemblages that record both shifting ice-flow direction through time and shifting subglacial conditions. Each assemblage formed, or modified, during times of dynamic (warm-based) ice, and later preserved under conditions below or close to the pressure melting point (slow and sluggish, or cold-based).
DS202005-0733
2020
Geballe, Z.M., Sime, N., Badro, J., van Keken, P.E., Goncharov, A.F.Thermal conductivity near the bottom of the Earth's lower mantle: measurements of pyrolite up to 120 Gpa and 2500 K.Earth and Planetary Science Letters, Vol. 536, 116161, 11p. PdfMantlegeothermometry

Abstract: Knowledge of thermal conductivity of mantle minerals is crucial for understanding heat transport from the Earth's core to mantle. At the pressure-temperature conditions of the Earth's core-mantle boundary, calculations of lattice thermal conductivity based on atomistic models have determined values ranging from 1 to 14 W/m/K for bridgmanite and bridgmanite-rich mineral assemblages. Previous studies have been performed at room temperature up to the pressures of the core-mantle boundary, but correcting these to geotherm temperatures may introduce large errors. Here we present the first measurements of lattice thermal conductivity of mantle minerals up to pressures and temperatures near the base of the mantle, 120 GPa and 2500 K. We use a combination of continuous and pulsed laser heating in a diamond anvil cell to measure the lattice thermal conductivity of pyrolite, the assemblage of minerals expected to make up the lower mantle. We find a value of W/m/K at 80 GPa and 2000 to 2500 K and 5.9 W/m/K at 124 GPa and 2000 to 3000 K. These values rule out the highest calculations of thermal conductivity of the Earth's mid-lower mantle (i.e. W/m/K at 80 GPa), and are consistent with both the high and low calculations of thermal conductivity near the base of the lower mantle.
DS202004-0514
2020
Gebralle, Z.M., Sime, N., Badro, J., van Kekn, P.E.Thermal conductivity near the bottom of the Earth's lower mantle: mesurements of pyrolite up to 120 GPa and 2500 K. Earth and Planetary Science Letters, Vol. 536, 116161 7p. PdfMantlegeothermometry

Abstract: Knowledge of thermal conductivity of mantle minerals is crucial for understanding heat transport from the Earth's core to mantle. At the pressure-temperature conditions of the Earth's core-mantle boundary, calculations of lattice thermal conductivity based on atomistic models have determined values ranging from 1 to 14 W/m/K for bridgmanite and bridgmanite-rich mineral assemblages. Previous studies have been performed at room temperature up to the pressures of the core-mantle boundary, but correcting these to geotherm temperatures may introduce large errors. Here we present the first measurements of lattice thermal conductivity of mantle minerals up to pressures and temperatures near the base of the mantle, 120 GPa and 2500 K. We use a combination of continuous and pulsed laser heating in a diamond anvil cell to measure the lattice thermal conductivity of pyrolite, the assemblage of minerals expected to make up the lower mantle. We find a value of W/m/K at 80 GPa and 2000 to 2500 K and 5.9 W/m/K at 124 GPa and 2000 to 3000 K. These values rule out the highest calculations of thermal conductivity of the Earth's mid-lower mantle (i.e. W/m/K at 80 GPa), and are consistent with both the high and low calculations of thermal conductivity near the base of the lower mantle.
DS202010-1844
2020
Genish, H., Ganesan, K., Stacey, A., Prawer, S., Rosenbluh, M.Effect of radiation damage on the quantum optical properties of nitrogen vacancies in diamond.Diamond & Related Materials, Vol. 109, 108049, 6p. PdfMantlenitrogen

Abstract: Single crystal diamond (<5?ppm nitrogen) containing native NV centers with coherence time of 150??s was irradiated with 2?MeV alpha particles, with doses ranging from 1012 ion/cm2 to 1015 ion/cm2. The effect of ion damage on the coherence time of NV centers was studied using optically detected magnetic resonance and supplemented by fluorescence and Raman microscopy. A cross-sectional geometry was employed so that the NV coherence time could be measured as a function of increasing defect concentration along the ion track. Surprisingly, although the ODMR contrast was found to decrease with increasing ion induced vacancy concentration, the measured decoherence time remained undiminished at 150us despite the estimated vacancy concentration reaching a value of 40?ppm at the end of range. These results suggest that ion induced damage in the form of an increase in vacancy concentration does not necessarily result in a significant increase in the density of the background spin bath.
DS202003-0339
2020
Geological Survey of IndiaMineral resources of India. ( first 19p. Kimberlites )Geological Survey of India, 75p. PdfIndiadiamond

Abstract: India has a rich tradition of mineral exploration. Innumerable old workings, mine dumps slag heaps, etc. are the tell tale signs of this glorious tradition. The flourishing diamond trade in the Deccan peninsula, mainly in the Golconda kingdom, had attracted world’s attention during historical time. Copper and gold were also used locally since the days of Indus Valley civilizations. East India Company started exploration for coal in the Eighteenth century with setting up of , the premier Earth science organisation and the second oldest survey of the country, in 1851 for the systematic geological survey and prospecting for coal. India was a notable producer of gold in the early part of twentieth century and major exporter of mica, sillimanite, kyanite, magnetite and chromite. Metallurgical industry started with the setting up of steel plants at Burnpur, Jamshedpur and copper smelter at Ghatsila. Second World War created great demand for various minerals and metals including those of strategic importance e.g., tungsten. Industrial policy, formulated after Independence, brought about a radical change in the mining and metallurgical industry. During the post-Independence period, GSI has embarked upon the exploration for minerals, particularly in favourable geological milieu spread over Dharwar, Bastar, Singhbhum and Aravalli cratons. The investigations carried out since 1960s provide us firsthand information of different mineral occurrences as well as their potential. Keeping in tune with the modern trends of mineral exploration, the GSI oriented its programmes through multidisciplinary surveys. From time to time it equipped itself with state-of-the-art laboratories to back up its various exploration programmes. The efforts have led to discovery of several mineral deposits in virgin areas in different parts of the country. A few other central and state government organisations were also involved in mineral exploration now and then, mostly in collaboration with foreign organisations. The liberalisation of India’s National Mineral Policy in 1993 paved the way for the entry of private entrepreneurs, including those from overseas for carrying out mineral exploration. The database developed by GSI has been found very useful for taking investment decisions by the Multi-National Companies.
DS202012-2216
2020
GeologypageNatural nanodiamonds in oceanic rocks.Geologypage.com, http://www.geologypage .com/2020/10/natural- nanodiamonds-in- oceanic-rocks.html Globalnanodiamonds

Abstract: Natural diamonds can form through low pressure and temperature geological processes on Earth, as stated in an article published in the journal Geochemical Perspectives Letters. The newfound mechanism, far from the classic view on the formation of diamonds under ultra-high pressure, is confirmed in the study, which draws on the participation of experts from the Mineral Resources Research Group of the Faculty of Earth Sciences of the University of Barcelona (UB).
DS202002-0188
2019
Ghent, E.D., Edwards, B.R., Russell, J.K.Pargasite bearing vein in spinel lherzolite from the mantle lithosphere of the North American Cordillera. Canadian Journal of Earth Sciences, Vol. 56, pp. 870-885.Canada, British Columbialherzolite

Abstract: Basanite lavas near Craven Lake, British Columbia, host a spinel lherzolite xenolith containing cross-cutting veins with pargasitic amphibole (plus minor apatite). The occurrence of vein amphibole in spinel lherzolite is singular for the Canadian Cordillera. The vein crosscuts foliated peridotite and is itself cut by the basanite host. The amphibole is pargasite, which is the most common amphibole composition in mantle peridotite. Rare earth element concentrations in the pargasite are similar to those for mafic alkaline rocks across the northern Cordilleran volcanic province (light rare earth elements ?50× chondrite and heavy rare earth elements ?5× chondrite). Two-pyroxene geothermometry suggests that the vein and host peridotite were thermally equilibrated prior to sampling by the basanite magma. Calculated temperature conditions for the sample, assuming equilibration along a model steady-state geotherm, are between 990 and 1050 °C and correspond to a pressure of 0.15 GPa (?52 ± 2 km depth). These conditions are consistent with the stability limits of mantle pargasite in the presence of a fluid having XH2O < ?0.1. The pargasite vein and associated apatite provide direct evidence for postaccretion fracture infiltration of CO2-F-H2O-bearing silicate fluids into the Cordilleran mantle lithosphere. Pargasite with low aH2O is in equilibrium with parts per million concentrations of H2O in mantle olivine, potentially lowering the mechanical strength of the lithospheric mantle underlying the Cordillera and making it more susceptible to processes such as lithospheric delamination. Remelting of Cordilleran mantle lithosphere containing amphibole veins may be involved in the formation of sporadic nephelinite found in the Canadian Cordillera.
DS202004-0515
2020
Gibson, S.A., Rooks, E.E., Day, J.A., Petrone, C.M., Leat, P.T.The role of sub-continental mantle as both "sink" and "source" in deep Earth volatile cycles.Geochimica et Cosmochimica Acta, Vol. 275, pp. 140-162.Mantlecraton

Abstract: The extent to which Earth’s sub-continental lithospheric mantle modulates the flux of volatile elements from our planet’s deep interior to its atmosphere (via volcanism) is poorly constrained. Here, we focus on "off-craton" sub-continental lithospheric mantle because this long-lived reservoir potentially acts as both a volatile “sink” and “source” during major heating and rifting events. The sub-continental lithospheric mantle is primarily formed of peridotites with subordinate amounts of pyroxenites. While both lithologies are dominated by nominally-volatile-free mantle minerals, some of these phases have been shown to contain non-negligible amounts of H2O (e.g. 100’s of ppmw in clinopyroxene). Data for volatile elements other than Li are, however, limited. We present new, high-precision, in-situ Secondary Ion Mass Spectrometry analyses of H, F, Cl, Li and B in olivine and pyroxenes from well-characterised garnet- and spinel-bearing peridotites and pyroxenites (from southern Patagonia and the Antarctic Peninsula). Our study confirms that clinopyroxene is the main host of H2O and F. The maximum F contents we report (up to 154 ppmw) are higher than those in previous studies and occur in Ti-Cr diopsides in highly-metasomatised peridotites and Ti-Al augites from clinopyroxenite veins. Water contents of clinopyroxenes (up to 615 ppmw) are within the range previously published for continental mantle. Lithium concentrations are low (<5 ppmw) in all analysed phases and both Cl and B are below detection levels (14 ppmw and 0.03 ppmw, respectively). Unique to our study is the large variation in major- and trace-element concentrations of the clinopyroxenes, which allows us to place quantitative constraints on how volatiles are stored in the mantle. We demonstrate that: (i) F contents of clinopyroxenes closely correlate with Ti and (ii) and is systematic and inversely correlated with temperature. Despite the redistribution of volatiles during sub-solidus re-equilibration, we show that the first order control on the concentration of volatiles in clinopyroxene is the style of metasomatism, i.e. channellised flow versus reactive percolation. The mean bulk volatile contents of peridotites from Pali Aike and the Antarctic Peninsula (H2O?=?89?±?31 ppmw, F?=?16?±?11.2 ppmw and Li?=?2?±?0.7 ppmw) are within the range previously published for continental "off-craton" mantle. The pyroxenites have significantly higher mean bulk concentrations of H2O (260?±?59 ppmw), F (86?±?43 ppmw) and Li (1.0?±?0.35 ppmw). While the greater capacity of mantle pyroxenites to host H2O relative to the associated peridotites has previously been observed in global "off-craton" mantle xenolith suites (e.g. Oahu, Hawaii; eastern China and the Rio Grande Rift, SW USA), here we show for the first time that pyroxenites are also major hosts of F (but not Cl, Li or B). Because of their relatively low solidus temperatures, pyroxenites in "off-craton" settings will be readily re-mobilised during lithospheric extension (and heating). We suggest these pyroxene-rich mantle lithologies may be responsible for the elevated concentrations of H2O and F observed in basalts and volcanic gasses from major continental rift zones and flood basalt provinces, and hence an important consideration in models of global volatile cycles.
DS202004-0516
2020
Giovannini, A.L., Mitchell, R.H., Bastos Neto, A.C., Moura, C.A.V., Pereira, V.P., Porto, C.G.Mineralogy and geochemistry of the Morro dos Seis Lagos siderite carbonatite, Amazonas, Brazil.Lithos, vol. 360-361, 105433 20p. PdfSouth America, Brazil, Amazonascarbonatite

Abstract: The Morro dos Seis Lagos niobium rare earth element, Ti-bearing lateritic deposit (Amazonas, Brazil) is derived from a primary siderite carbonatite. The complex is the only example of a Nb deposit in which Nb-rich rutile is the main Nb ore mineral. Apart from the laterites, at the current level of exposure the complex consists only of siderite carbonatite; silicate rocks are absent. Three types of siderite carbonatite are recognized: (1) a brecciated and oxidized core siderite carbonatite consisting of up to 95 vol% siderite together with: hematite; pyrochlore; Nb-brookite; Ti-maghemite; and thorobastnäsite; (2) a REE- and P-rich variety of the core siderite carbonatite consisting of siderite (up to 95 vol%), hematite, minor pyrochlore, monazite and bastnäsite; (3) a border hydrothermal siderite carbonatite with ~70 vol% siderite, barite (~15 vol%), gorceixite (~7 vol%) and minor rhabdophane and pyrochlore. The country rock gneiss in which the carbonatite was emplaced was affected by potassic fenitization, with the formation of phlogopite and orthoclase together with monazite, fluorapatite and bastnäsite. The siderite carbonatites exhibit a wide variation of ?13C (?5.39‰ to ?1.40‰), accompanied by a significant variation in ?18O (17.13‰ to 31.33‰), especially in the REE-rich core siderite carbonatite, and are explained as due to the presence of both H2O and CO2 in the magma. The core siderite carbonatite is the richest in Fe (48.64-70.85 wt% Fe2O3) and the poorest in Ca (up 0.82 wt% CaO) example of a siderite carbonatite yet recognized The ferrocarbonatite has significant contents of Mn, Ba, Th, Pb and LREE, and a very high Nb (up to 7667 ppm) content due to the presence of Nb-brookite. The substitution 3Ti4+ = Fe2+ + 2Nb5+ recognized in Nb-rich brookite explains enrichment of Nb in the core siderite carbonatite and indicates formation in a reducing environment. The high Nb/Ta ratio (1408-11,459) of the carbonatite is compatible with residual liquids derived by fractional crystallization. The 87Sr/86Sr (0.70411-0.70573) and 144Nd/143Nd (0.512663-0.512715) isotopic data suggest the carbonatite is mantle-derived with essentially no crustal contamination and is younger than the maximum age of 1328 ± 58 Ma (UPb in zircon). We suggest that the Morro dos Seis Lagos carbonatite complex represents the upper-most parts of a differentiated carbonatite magmatic system, and that the siderite carbonatite is related to late-magmatic-to-carbo-hydrothermal processes.
DS202008-1393
2020
Giuliani, A., Jackson, M.G., Fitzpayne, A.The role of FOZO-PREMA in kimberlite genesis. Goldschmidt 2020, 1p. AbstractMantlekimberlite

Abstract: FOZO-PREMA is an ubiquitous component of oceanic basalts and was originally defined by the convergence of Sr- Nd-Pb isotope trends of ocean island basalts (OIBs) from individual island-seamount chains [1]. FOZO-PREMA is also widespread in juvenile continental magmas, which argue for a global relevance of this component irrespective of the tectonic settings. Early studies proposed that FOZO-PREMA could be a physically discrete reservoir derived from depletion of primitive mantle based on the combination of geochemically depleted 143Nd/144Nd combined with elevated 3He/4He ratios [2]. Conversely, later models showed that isotopic compositions spanning the FOZO-PREMA field can be obtained by mixing recycled oceanic crust and mantle material previously depleted by crust extraction [3]. Kimberlites can provide a new perspective on this debate because a recent study of the Nd and Hf isotope compositions of kimberlite through time shows that these magmas sample a deep, long-lived, homogeneous reservoir, which might contain remnants of early Earth differentiation processes [4]. We critically review the Sr, Nd and Hf isotope compositions of kimberlites that were emplaced from ~2.1 Ga. After screening kimberlite isotopic data for the effects of lithospheric contamination and secondary alteration, we show that kimberlites through time have been derived from a mantle source with FOZO-PREMA composition. This observation makes it unlikely that FOZO-PREMA derives from continuous mixing of depleted and recycled components because the composition of subducted lithologies, pressure and temperature conditions in subduction zones, and temperature and oxygen fugacity conditions of the convective mantle have changed throughout Earth history. We therefore conclude that FOZO-PREMA is a long-lived component of Earth’s mantle, which must have existed for at least the last 2.1 Ga, the wider implications of which will be discussed.
DS202007-1142
2020
Giuliani, A., Pearson, D.G., Soltys, A., Dalton, H., Phillips, D., Foley, S.F., Lim, E.Kimberlite genesis from a common primary melt modified by lithospheric mantle assimilation.Science Advances, Vol. 6, eeaz0424Mantlemelting

Abstract: Quantifying the compositional evolution of mantle-derived melts from source to surface is fundamental for constraining the nature of primary melts and deep Earth composition. Despite abundant evidence for interaction between carbonate-rich melts, including diamondiferous kimberlites, and mantle wall rocks en route to surface, the effects of this interaction on melt compositions are poorly constrained. Here, we demonstrate a robust linear correlation between the Mg/Si ratios of kimberlites and their entrained mantle components and between Mg/Fe ratios of mantle-derived olivine cores and magmatic olivine rims in kimberlites worldwide. Combined with numerical modeling, these findings indicate that kimberlite melts with highly variable composition were broadly similar before lithosphere assimilation. This implies that kimberlites worldwide originated by partial melting of compositionally similar convective mantle sources under comparable physical conditions. We conclude that mantle assimilation markedly alters the major element composition of carbonate-rich melts and is a major process in the evolution of mantle-derived magmas.
DS202003-0340
2019
Giuliani, G., Groat, L.A.Geology of corundum and emerald gem deposits: a review.Gems & Gemology, Vol. 55, 4, pp. 464-511.Africa, Madagascar, Zambia, Asia, Sri Lanka, South America, Colombiaemerald

Abstract: The great challenge of geographic origin determination is to connect the properties and features of individual gems to the geology of their deposits. Similar geologic environments can produce gems with similar gemological properties, making it difficult to find unique identifiers. Over the last two decades, our knowledge of corundum and emerald deposit formation has improved significantly. The mineral deposits are classically separated into primary and secondary deposits. Primary corundum deposits are subdivided into two types based on their geological environment of formation: (1) magmatic and (2) metamorphic. Magmatic deposits include gem corundum in alkali basalts as in eastern Australia, and sapphire in lamprophyre and syenite as in Montana (United States) and Garba Tula (Kenya), respectively. Metamorphic deposits are divided into two subtypes (1) metamorphic deposits sensu stricto (in marble; mafic and ultramafic rocks, or M-UMR), and (2) metamorphic-metasomatic deposits characterized by high fluid-rock interaction and metasomatism (i.e., plumasite or desilicated pegmatites in M-UMR and marble, skarn deposits, and shear zonerelated deposits in different substrata, mainly corundum-bearing Mg-Cr-biotite schist). Examples of the first subtype include the ruby deposits in marble from the Mogok Stone Tract or those in M-UMR from Montepuez (Mozambique) and Aappaluttoq (Greenland). The second subtype concerns the sapphire from Kashmir hosted by plumasites in M-UMR. Secondary corundum deposits (i.e., present-day placers) result from the erosion of primary corundum deposits. Here, corundum is found in the following types of deposits: eluvial (derived by in situ weathering or weathering plus gravitational movement), diluvial (scree or talus), colluvial (deposited at the base of slopes by rainwash, sheetwash, slow continuous downslope creep, or a combination of these processes), and alluvial (deposited by rivers). Today, most sapphires are produced from gem placers related to alkali basalts, as in eastern Australia or southern Vietnam, while placers in metamorphic environments, such as in Sri Lanka (Ratnapura, Elahera) and Madagascar (Ilakaka), produce the highest-quality sapphires. The colluvial Montepuez deposit in Mozambique provides a huge and stable supply of clean and very high-quality rubies. Primary emerald deposits are subdivided into two types based on their geological environment of formation: (1) tectonic-magmatic-related (Type I) and (2) tectonic-metamorphic-related (Type II). Several subtypes are defined and especially Type IA, hosted in M-UMR, which accounts for about 70% of worldwide production (Brazil, Zambia, Russia, and others). It is characterized by the intrusion of pegmatites or quartz veins in M-UMR accompanied by huge hydrothermal fluid circulation and metasomatism with the formation of emerald-bearing desilicated pegmatite (plumasite) and biotite schist. Type IB in sedimentary rocks (China, Canada, Norway, Kazakhstan, and Australia) and Type IC in granitic rocks (Nigeria) are of minor importance. The subtype Type IIA of metamorphic deposits is related to hydrothermal fluid circulation at high temperature, in thrust fault and/or shear zones within M-UMR of volcano-sedimentary series, such as at the Santa Terezinha de Goiás deposit in Brazil. The subtype Type IIB is showcased by the Colombian emerald deposits located in the Lower Cretaceous black shales of the Eastern Cordillera Basin. These are related to the circulation of hydrothermal basinal fluids in black shales, at 300330°C, that dissolved evaporites in (1) thrust and tear faults for the deposits of the western emerald zone (Yacopi, Coscuez, Muzo, Peñas Blancas, Cunas, and La Pita mines) and (2) a regional evaporite level intercalated in the black shales or the deposits of the eastern emerald zone (Gachalá, Chivor, and Macanal mining districts). Secondary emerald deposits are unknown because emerald is too fragile to survive erosion and transport in rivers.
DS202007-1143
2020
Gladkochub, D.P., Donskaya, T.V.Geochemical composition of dolerites as an indicator of the distance of a dike swarm from the mantle plume center ( case study of Proterozoic dike swarms, Siberian craton).Doklady Earth Sciences, Vol. 491, pp. 243-246.Russia, Siberiadyke

Abstract: Based on investigation of Proterozoic mafic dike swarms of the Siberian Craton, we inferred how the geochemical and isotopic characteristics of dike swarms of dolerites of Large Igneous Provinces depend on their distance from the mantle plume head. It has been found that the dolerite parent melts near the mantle plume head correspond to OIB compositions. At significant distances from the plume, the initial melts of dolerites are generated in the subcontinental lithospheric mantle, which provides a wide range of their compositions differing from typical OIB and do not indicate directly the genetic relationship of these mafic rocks with the mantle plume.
DS202008-1394
2020
Goes, S., Hasterok, D., Schutt, D.L., Klocking, M.Continental lithospheric temperatures: a review.Physics of the Earth and Planetary Interiors, Vol. 306, 106509, 18p. PdfMantlegeothermometry

Abstract: Thermal structure of the lithosphere exerts a primary control on its strength and density and thereby its dynamic evolution as the outer thermal and mechanic boundary layer of the convecting mantle. This contribution focuses on continental lithosphere. We review constraints on thermal conductivity and heat production, geophysical and geochemical/petrological constraints on thermal structure of the continental lithosphere, as well as steady-state and non-steady state 1D thermal models and their applicability. Commonly used geotherm families that assume that crustal heat production contributes an approximately constant fraction of 25-40% to surface heat flow reproduce the global spread of temperatures and thermal thicknesses of the lithosphere below continents. However, we find that global variations in seismic thickness of continental lithosphere and seismically estimated variations in Moho temperature below the US are more compatible with models where upper crustal heat production is 2-3 times higher than lower crustal heat production (consistent with rock estimates) and the contribution of effective crustal heat production to thermal structure (i.e. estimated by describing thermal structure with steady-state geotherms) varies systematically from 40 to 60% in tectonically stable low surface heat flow regions to 20% or lower in higher heat flow tectonically active regions. The low effective heat production in tectonically active regions is likely partly the expression of a non-steady thermal state and advective heat transport.
DS202001-0013
2019
Goldie, R.Approximation of Tiffany & Co. seasonally - adjusted, quarterly sales per store ( sales x $ 000). Raymondgoldie @outlook.com, Dec. 6, 1p. GraphGlobalTiffany
DS202008-1395
2019
Golovin, A.V., Sharygin, I., Korsakov, A.V., Abersteiner, A.Can primitive kimberlitic melts be alkali-carbonate liquids: composition of the melt snapshots preserved in deepest mantle xenoliths.Journal of Raman Spectroscopy, doi.org/10.1002/jrs.5701 19p pdfRussiadeposit - Udachnaya-East

Abstract: The study of kimberlite rocks is important as they provide critical information regarding the composition and dynamics of the continental mantle and are the principal source of diamonds. Despite many decades of research, the original compositions of kimberlite melts, which are thought to be derived from depths > 150 km, remain highly debatable due to processes that can significantly modify their composition during ascent and emplacement. Snapshots of the kimberlite?related melts were entrapped as secondary melt inclusions hosted in olivine from sheared peridotite xenoliths from the Udachnaya?East pipe (Siberian craton). These xenoliths originated from 180? to 220?km depth and are among the deepest derived samples of mantle rocks exposed at the surface. The crystallised melt inclusions contain diverse daughter mineral assemblages (>30 mineral species), which are dominated by alkali?rich carbonates, sulfates, and chlorides. The presence of aragonite as a daughter mineral suggests a high?pressure origin for these inclusions. Raman?mapping studies of unexposed inclusions show that they are dominated by carbonates (>65 vol.%), whereas silicates are subordinate (<13 vol.%). This indicates that the parental melt for the inclusions was carbonatitic. The key chemical features of this melt are very high contents of alkalis, carbon dioxide, chlorine, and sulfur and extremely low silica and water. Alkali?carbonate melts entrapped in xenolith minerals likely represent snapshots of the primitive kimberlite melt. This composition is in contrast with the generally accepted notion that kimberlites originated as ultramafic silicate water?rich melts. Experimental studies revealed that alkali?carbonate melts are a very suitable diamond?forming media. Therefore, our findings support the idea that some diamonds and kimberlite magmatism may be genetically related.
DS202008-1396
2020
Gonzales-Jiminez, J.M., Tassara, S., Schettino, E., Roque-Rosell, J., Farre-de-Pablo, J., Saunders, J.E., Deditius, A.P., Colas, V., Rovira-Medina, J.J., Guadalupe Davalos, M., Schilling, M., Jiminez-Franco, A., Marchesi, C., Nieto, F., Proenza, J.A., GerMineralogy of the HSE in the subcontinental lithospheric mantle - an interpretive review.Lithos, in press available, 44p. PdfMantleHSE

Abstract: The highly siderophile elements (HSE: Os, Ir, Ru, Rh, Pt, Pd, Re, Au) exist in solid solution in accessory base-metal sulfides (BMS) as well as nano-to-micron scale minerals in rocks of the subcontinental lithospheric mantle (SCLM). The latter include platinum-group minerals (PGM) and gold minerals, which may vary widely in morphology, composition and distribution. The PGM form isolated grains often associated with larger BMS hosted in residual olivine, located at interstices in between peridotite-forming minerals or more commonly in association with metasomatic minerals (pyroxenes, carbonates, phosphates) and silicate glasses in some peridotite xenoliths. The PGM found inside residual olivine are mainly Os-, Ir- and Ru-rich sulfides and alloys. In contrast, those associated with metasomatic minerals or silicate glasses of peridotite xenoliths consist of Pt, Pd, and Rh bonded with semimetals like As, Te, Bi, and Sn. Nanoscale observations on natural samples along with the results of recent experiments indicate that nucleation of PGM is mainly related with the uptake of HSE by nanoparticles, nanominerals or nanomelts at high temperature (> 900?°C) in both silicate and/or sulfide melts, regardless of the residual or metasomatic origin of their host minerals. A similar interpretation can be assumed for gold minerals. Our observations highlight that nanoscale processes play an important role on the ore-forming potential of primitive mantle-derived magmas parental to magmatic-hydrothermal deposits enriched in noble metals. The metal inventory in these magmas could be related with the physical incorporation of HSE-bearing nanoparticles or nanomelts during processes of partial melting of mantle peridotite and melt migration from the mantle to overlying continental crust.
DS202010-1845
2020
Gordeychik, B., Churikova, T., Shea, T., Kronz, A,m Simakin, A., Worner, G.Fo and Ni relations in olivine differentiate between crystallization and diffusion trends.Journal of Petrology, 10.1093/petrology/egaa083Mantleolivine

Abstract: Nickel is a strongly compatible element in olivine, and thus fractional crystallization of olivine typically results in a concave-up trend on a Fo-Ni diagram. "Ni-enriched" olivine compositions are considered those that fall above such a crystallization trend. To explain Ni-enriched olivine crystals, we develop a set of theoretical and computational models to describe how primitive olivine phenocrysts from a parent (high-Mg, high-Ni) basalt re-equilibrate with an evolved (low-Mg, low-Ni) melt through diffusion. These models describe the progressive loss of Fo and Ni in olivine cores during protracted diffusion for various crystal shapes and different relative diffusivities for Ni and Fe-Mg. In the case when the diffusivity of Ni is lower than that for Fe-Mg interdiffusion, then olivine phenocrysts affected by protracted diffusion form a concave-down trend that contrasts with the concave-up crystallization trend. Models for different simple geometries show that the concavity of the diffusion trend does not depend on the size of the crystals and only weakly depends on their shape. We also find that the effect of diffusion anisotropy on trend concavity is in the same magnitude as the effect of crystal shape. Thus, both diffusion anisotropy and crystal shape do not significantly change the concave-down diffusion trend. Three-dimensional numerical diffusion models using a range of more complex, realistic olivine morphologies with anisotropy corroborate this conclusion. Thus, the curvature of the concave-down diffusion trend is mainly determined by the ratio of Ni and Fe-Mg diffusion coefficients. The initial and final points of the diffusion trend are in turn determined by the compositional contrast between mafic and more evolved melts that have mixed to cause disequilibrium between olivine cores and surrounding melt. We present several examples of measurements on olivine from arc basalts from Kamchatka, and several published olivine datasets from mafic magmas from non-subduction settings (lamproites and kimberlites) that are consistent with diffusion-controlled Fo-Ni behaviour. In each case the ratio of Ni and Fe-Mg diffusion coefficients is indicated to be?
DS202010-1846
2020
Gorojovsky, L., Alard, O.Optimization of laser and mass spectrometer parameters for the in situ analysis of Rb/Sr ratios by LA-ICP-MS/MS. ( mentions Monastery phlogopite megacrystJournal of Analytical Atomic Spectrometry, 10.1039/DOJA00308E 15p. PdfGlobalgeochronology

Abstract: The Rb-Sr isotopic system is widely used in geochronology. Conventionally burdened by the isobaric overlap of 87Rb and 87Sr, Rb/Sr dating in situ has only recently become achievable with the newly developed LA-ICP-MS/MS system. Simultaneous use of reactive gas (e.g. O2, N2O, or CH3F) during LA-ICP-MS/MS analysis has been shown to resolve the Rb and Sr overlap, thus now making available key spatial and temporal information that can only be accessed via in situ analytical techniques. The accuracy and precision of Rb/Sr ratios and ages are largely dependent on the laser and ICP-MS/MS parameters used. Rb/Sr isotopic analysis by LA-ICP-MS/MS is a recently developed technique and these parameters are yet to be fully explored. We investigate the effects of laser wavelength (213 nm and 193 nm), laser frequency (5 Hz and 10 Hz), laser carrier gas (He, H2, and N2), dwell time, and external standard calibration on the accuracy and precision of 87Rb/86Sr and 87Sr/86Sr ratios and ages. These analytical conditions have been tested on the commercially available reference materials: NIST SRM 610, USGS BHVO-2G, and pressed nano-particulate powder tablet CRPG Mica-mg, as well as a Monastery phlogopite megacryst. Our results show that accuracy and precision for 87Rb/86Sr and 87Sr/86Sr ratios are significantly affected by laser wavelength and frequency. Variation in these parameters can strongly magnify any matrix effects which directly influences the ability to apply effective external corrections. We obtain the best accuracy and precision when using a 193 nm laser wavelength, ablating at a frequency of 5 Hz (0.30 2s% and 0.15 2s% for 87Rb/86Sr and 87Sr/86Sr ratios, respectively). Meanwhile we find that age accuracy is highly dependant on external reference materials. When these analytical settings are put to test on the Monastery phlogopite, we obtain an age of 90.0 ± 3.6 (0.24% accuracy) when using mica-mg (87Rb/86Sr) and NIST 610 (87Sr/86Sr) as external standards.
DS202002-0189
2019
Goss, H.The shape of the world.EOS, 100, Dec. 31, http://doi.org/ 10.1029/2019EO138179Mantlegeodynamics
DS202008-1397
2020
Goss, H.A dive into the deep Earth.Eos, 101, doi.org/10.1029 /2020EO145467 1p. Mantlemineralogy

Abstract: In July, Eos looks at the incredible capabilities scientists have developed to recreate the enormous pressures and temperatures that exist far below the planet’s surface.
DS202005-0734
2020
Gramling, C.Plate tectonics may have started 400 million years earlier than we thought. sciencemag.org, April 22, 3p.AustraliaTectonics

Abstract: Modern plate tectonics may have gotten under way as early as 3.2 billion years ago, about 400 million years earlier than scientists thought. That, in turn, suggests that the movement of large pieces of Earth’s crust could have played a role in making the planet more hospitable to life. Geologist Alec Brenner of Harvard University and his colleagues measured the magnetic orientations of iron-bearing minerals in the Honeyeater Basalt, a layer of rock that formed between 3.19 billion and 3.18 billion years ago. The basalt is part of the East Pilbara Craton, an ancient bit of continent in Western Australia that includes rocks as old as 3.5 billion years. This craton, the researchers found, was on the move between 3.35 billion and 3.18 billion years ago, drifting around the planet at a rate of at least 2.5 centimeters per year. That’s a speed comparable to modern plate motions, the team reports April 22 in Science Advances.
DS202008-1398
2020
Greene, S., Jacob, D.E., O'Reilly, S.Y., Henry, H., Pinter, Z., Heaman, L.Extensive prekimberlitic lithosphere modification recorded in Jericho mantle xenoliths in kimberlites, Slave Craton.Goldschmidt 2020, 1p. AbstractCanada, Northwest Territoriesdeposit - Jericho

Abstract: Wehrlite and pyroxenite xenoliths and megacrysts from the Jericho kimberlite were analyzed by ?XRF and EBSD, and for major elements, trace elements, and isotopes (Pb-Sr- O) in major phases. Thermobarometry places these samples at 60 - 180 km and 600 - 1200 ??C. While modes and textures vary, many samples have olivine-olivine grain boundaries with straight edges and 120° angle junctions, indicating granoblastic recrystallisation, while clinopyroxene and orthopyroxene are complexly intergrown. Clinopyroxene twins and subgrains recording orientations distinct from the encapsulating grain were detected using EBSD and are inferred to represent recent modification processes. Several distinct garnet compositions were measured, with multiple thin garnet rims in some samples suggesting possible successive stages of garnet crystallisation. Complex chromium zoning in garnet is detected by ?XRF in several samples (fig.1). Pb-Pb ages for most samples are similar to the age of kimberlite entrainment (173 Ma), but the shallowest pyroxenite sample preserves the most radiogenic Pb composition, intercecting concordia at 0.7 - 1.1 Ga, and is the only sample with ?18O above the mantle range (6.2±0.1 ‰). The deepest sample has the lowest ?18O (5.5±0.1 ‰) and radiogenic 87Sr/86Sr similar to MARID rocks (0.709±1 ‰). These results suggest the Jericho lithosphere experienced several melt/fluid injection events that modified substantial portions of the sampled section soon before kimberlite entrainment.
DS202011-2039
2020
Gress, M.U., Koorneef, J.M., Thomassot, E., Chinn, I.L., van Zuilen, K., Davies, G.R.Sm-Nd isochron ages coupled with C-N isotope data of eclogitic diamonds from Jwaneng, Botswana.Geochimica et Cosmochimica Acta, 10.1016/j.gca.2020.10.010 35p. PdfAfrica, Botswanadeposit - Jwaneng

Abstract: Constraining the formation age of individual diamonds from incorporated mineral inclusions and assessing the host diamonds’ geochemical characteristics allows determination of the complex history of diamond growth in the sub-continental lithospheric mantle (SCLM). It also provides the rare opportunity to study the evolution of the deep cycling of volatiles over time. To achieve these aims, Sm-Nd isotope systematics are presented for 36 eclogitic garnet and clinopyroxene inclusions from 16 diamonds from the Jwaneng mine, Botswana. The inclusions and host diamonds comprise at least two compositional suites that record different ‘mechanisms’ of diamond formation and define two isochrons, one Paleoproterozoic (1.8 Ga) and one Neoproterozoic (0.85 Ga). There are indications of at least three additional diamond-forming events whose ages currently cannot be well constrained. The Paleoproterozoic diamond suite formed by large-scale (> 100’s km), volatile-rich metasomatism related to formation and re-working of the Proto-Kalahari Craton. In contrast, the heterogeneous composition of the Neoproterozoic diamond suite indicates diamond formation on a small-scale, through local (< 10 km) equilibration of compositionally variable diamond-forming fluids in different eclogitic substrates during the progressive breakup of the Rodinia supercontinent. The results demonstrate that regional events appear to reflect the input of volatiles (i.e., carbon-bearing) derived from the asthenospheric mantle, whereas local diamond-forming events mainly promote the redistribution of volatiles within the SCLM. The occurrence of isotopically light carbon analysed in distinct growth zones from samples of this study (?13C < -21.1‰) provides further indication of a recycled origin for surface-derived carbon in some diamonds from Jwaneng. Determining Earth’s long-term deep carbon cycle using diamonds, however, requires an understanding of the nature and scale of specific diamond-forming events.
DS202012-2217
2020
Griffin, W.L., Gain, S.E.M., Saunders, M., Bindi, L., Alard, O., Toledo, V., O'Reilly, S.Y.Parageneses of TiB2 in corundum xenoliths from Mt. Carmel, Israel: siderophile behavior of boron under reducing conditions.American Mineralogist, Vol. 105, pp. 1609-1621. pdfEurope, Israeldeposit - Mt. Carmel

Abstract: Titanium diboride (TiB2) is a minor but common phase in melt pockets trapped in the corundum aggregates that occur as xenoliths in Cretaceous basaltic volcanoes on Mt. Carmel, north Israel. These melt pockets show extensive textural evidence of immiscibility between metallic (Fe-Ti-C-Si) melts, Ca-Al-Mg-Si-O melts, and Ti-(oxy)nitride melts. The metallic melts commonly form spherules in the coexisting oxide glass. Most of the observed TiB2 crystallized from the Fe-Ti-C silicide melts and a smaller proportion from the oxide melts. The parageneses in the melt pockets of the xenoliths require fO2 ? ?IW-6, probably generated through interaction between evolved silicate melts and mantle-derived CH4+H2 fluids near the crust-mantle boundary. Under these highly reducing conditions boron, like carbon and nitrogen, behaved mainly as a siderophile element during the separation of immiscible metallic and oxide melts. These parageneses have implications for the residence of boron in the peridotitic mantle and for the occurrence of TiB2 in other less well-constrained environments such as ophiolitic chromitites.
DS202001-0014
2019
Groat, L.A.Adding logic to luck: recent advances in coloured stone exploration in Canada.Journal of Gemmology, Vol. 36, pp. 620-633.Canadagemstones
DS202003-0341
2019
Groat, L.A., Giuilani, G.,, Stone-Sundberg, J., Sun, Z., Renfro, N.D., Palke, A.C.A review of analytical methods used in geographic origin determination of gemstones.Gems & Gemology, Vol. 55, 4, pp. 512-535.Globalemerald, sapphire

Abstract: Origin determination is of increasing importance in the gem trade. It is possible because there is a close relationship between the geological environment of formation and the physical and chemical properties of gemstones, such as trace element and isotopic compositions, that can be measured in the laboratory using combinations of increasingly sophisticated instrumentation. Origin conclusions for ruby, sapphire, and emerald make up the bulk of demand for these services, with growing demand for alexandrite, tourmaline, and spinel. However, establishing origin with a high degree of confidence using the capabilities available today is met with varying degrees of success. Geographic origin can be determined with a high level of confidence for materials such as emerald, Paraíba-type tourmaline, alexandrite, and many rubies. For some materials, especially blue sapphire and some rubies, the situation is more difficult. The main problem is that if the geology of two deposits is similar, then the properties of the gemstones they produce will also be similar, to the point where concluding an origin becomes seemingly impossible in some cases. Origin determination currently relies on a combination of traditional gemological observations and advanced analytical instrumentation.
DS202002-0190
2020
Grocholski, B.Synthesizing single-layer diamond: Carbon allotropes of diamond and graphene.Science, Vol. 367, 6476, p. 402.Globalcarbon

Abstract: The carbon allotropes of diamond and graphene have different types of bonding that lead to their exceptional properties. Bakharev et al. pull off the impressive trick of making a monolayer carbon film that is diamond-like in its bonding. The authors accomplish this by attaching fluorine atoms to the carbon film, creating “F-diamane.” Diamane is a long-sought-after, but challenging to make, material that should have useful properties. F-diamane may find use in a variety of applications, from microelectronics as a semiconductor to a seed material for growing single-crystal diamond films.
DS202009-1629
2020
Groves, D.I., Santosh, M.Craton and thick lithosphere margins: the sites of giant mineral deposits and mineral provinces. Not specific to diamonds.Gondwana Research, in press available 28p. PdfGlobalgeodynamics
DS202004-0517
2019
Gruber, B.H.Temperatures and heat production in the Slave Craton lower crust: evidence from exnoliths in the Diavik A-154 kimberlite.Thesis MSc University of Alberta , 123p. Pdf Canada, Northwest Territoriesdeposit - Diavik A-154

Abstract: Lower crustal heat production is poorly constrained due to the relative inaccessibility of lower crustal samples and their inherent complexity. To obtain the requisite information, the current project conducts spatially resolved geochemical analyses on minerals in 15 lower crustal xenoliths erupted via the Diavik A-154 kimberlite of the Northwest Territories, Canada. The aims are to: 1) conduct geothermometric measurements on lower crustal minerals, 2) construct a heatproducing element budget of the lower crust of the Slave craton, and 3) test the validity of these measurements in a parameter space relevant to geodynamic modeling and diamond exploration. The Diavik lower crustal xenolith suite comprises two main lithologies, mafic granulite (garnet-plagioclase-clinopyroxene ± orthopyroxene) and metasedimentary granulite (garnetplagioclase- orthopyroxene ± quartz ± K-feldspar ± kyanite), which are present in proportions of approximately 80:20, respectively. Application of mineral-pair, iron-magnesium exchange geothermometers (garnet-biotite, garnet-amphibole, and garnet-clinopyroxene) to these xenoliths indicates that the lower crust was at a maximum temperature of roughly 500 °C at the time of kimberlite eruption (~ 55 Ma). The actual temperature of the lower crust is likely lower than 500 °C as the geothermometers probably record the closure temperature of diffusional Fe2+-Mg exchange between touching mineral pairs rather than the ambient temperature of the rocks prior to their entrainment in the kimberlite magma. Heat-producing element (HPE) concentration measurements show that the lower crustal heat production of the Slave craton is likely 0.14 ± 0.02 ?W/m3, which is lower than most values in the literature but broadly comparable to some geophysical estimates. This estimate is the result of (20:80) bimodal mixing of idealized lower crustal endmembers: a metasedimentary lower crust (0.37 ± 0.06 ?W/m3) and a mafic lower crust (0.08 ± 0.01 ?W/m3). These endmembers were iii calculated via a reconstructed bulk rock calculation utilizing trace element concentrations of constituent lower crustal minerals and idealized lithologies from the lower crustal xenoliths. Using these heat production estimates and other crustal parameters such as continental heat flux, mantle heat flux, crustal thickness, and crustal thermal conductivity, I modeled a Moho temperature for the Slave craton of 425 °C, which is consistent with maximum lower crustal temperature estimate given by geothermometry. Adjusting the lower crustal heat production in the geotherm modeling program FITPLOT changes the temperature of the Moho in a similar fashion to the calculated models; however, the diamond propensity of the mantle lithosphere (partially a function of Moho temperature and heat production) does not appear to be strongly affected by a changing Moho temperature and is more strongly controlled by the conditions of the mantle P-T array.
DS202005-0735
2020
Gryaznov, I.A., Zhimulev, E.I., Sonin, V.M., Lindenblot, E.S., Chepurov, A.A.Morphological features of diamond crystals resulting from dissolution in a Fe-Ni-S melt under high pressure.Doklady Earth Sciences, Vol. 489, 2, pp. 1449-1452 .pdfRussiadiamond morphology, CLIPPIR

Abstract: The primary results are presented on the dissolution of plane-faced diamond crystals of octahedral habit in a Fe-Ni-S melt under 3.5 GPa and 1400°C. It was found that the dissolution resulted in the transformation of plane-faced into curve-faced individuals of morphological features characteristic for kimberlite diamonds. It was concluded that the diamond forms as such might have formed in reduced domains of the Earth’s mantle before becoming involved in the kimberlite magma.
DS202002-0191
2019
Guice, G.L.Origin and geodynamic significance of ultramafic- mafic complexes in the North Atlantic and Kaapvaal cratons.Thesis, Phd Cardiff University, 315p. PdfEurope, Africa, South Africacraton
DS202008-1399
2020
Gukurume, S., Nhodo, L.Forced displacements in mining communities: politics in Chiadzwa diamond area, Zimbabwe.Journal of Contemporary African Studies, Vol. 38, 1, pp. 39-54.Africa, Zimbabwedeposit - Chiadzwa

Abstract: The Chiadzwa diamonds attracted widespread attention due to human rights violations and illegal smuggling. When diamonds were discovered in 2006, thousands of artisanal miners descended on the diamond fields. In response, the government unleashed the army and police in brutal crackdowns to drive artisanal miners off the diamond fields. This militarisation of diamond fields and extraction was followed by forced displacement of the Chiadzwa people. This article examines the lived, everyday experiences of the displaced Chiadzwa people. Findings reveal that displacements dislocated the livelihoods and socialities of the people. Displacements also exacerbated people's vulnerability to livelihood shocks, insecurity, and poverty. In relocating people the government adopted a ‘top-down’ approach which triggered contestations and conflicts with the people who felt alienated from their ancestral land and excluded from diamond wealth. Consequently, sabotage, resistance and subversion were commonplace in the relocation process. These socio-political ‘tactics’ should be viewed as ‘weapons of the weak’.
DS202006-0921
2020
Gusev, N.I., Sergeeva, L. Yu., Larionov, A.N., Skublov, S.G.Relics of the Eoarchean continental crust of the Anabar shield, Siberian Craton.Petrology, Vol. 28, 2, pp. 118-140.Russiadeposit - Daldyn

Abstract: In the northern part of the Anabar Shield, orthopyroxene plagiogneisses of the granulite Daldyn Group host lenses of mafic rocks surrounded by melanocratic rims. According to their chemical composition, the mafic rocks correspond to subalkaline gabbro, the plagiogneisses correspond to granodiorites contaminated with mafic material, and the rims are diorites. The orthopyroxene plagiogneisses of granodiorite composition have 147Sm/144Nd = 0.1097, ?Nd(?) = 1.6, TNd(DM) = 3.47 Ga and are metamorphosed anatectic granitoids with an age of 3.34 Ga. The mafic rocks have high Zr, Th, and Pb contents, are enriched in REE (?REE = 636 ppm), with a high degree of fractionation [(La/Yb)N = 17.73] and a well-defined Eu minimum (Eu/Eu* = 0.51), and have 147Sm/144Nd = 0.099, ?Nd(?) = 1.4 and TNd(DM) = 3.65 Ga. It is assumed that these rocks crystallized from melt derived from an enriched mantle (plume) source. Based on U-Pb (SHRIMP-II) dating of 50 zircon grains from the mafic rocks, a group of grains with concordant ages from 3567 to 1939 Ma was distinguished, along with a large number of discordant values. Multiple measurements in zircon grains with discordant age values make it possible to identify seven grains of Eoarchean age, with upper intercepts of the discordia corresponding to 3987 ± 71 to 3599 ± 33 Ma. The Lu-Hf systematics of 14 zircon grains is characterized by ?Hf(T) = +3.7 and by close values of THf(DM) = 3.95 and TCHf = 3.93 Ga (3.99 Ga for the oldest zircon). The Paleoarchean (3.57 Ga) zircons are characterized by negative values of ?Hf(T) = -5.3 and -6.8, THf(DM) = 3.92-3.98 Ga, and TCHf = 4.14-4.24 Ga, which indicate recycling of the preexisting Eoarchean and Hadean continental crust. The younger zircon (3287-2410 Ma) was also formed when the preexisting crust was recycled.
DS202007-1144
2020
Haddock, D., Manya, S., Brown, R.J., Jones, T.J., Wadsworth, F.B., Dobson, K.J., Gernon, T.M.Syn-eruptive agglutination of kimberlite volcanic ash. PyroclastsVolcanica, Vol. 3, 1, pp. 169-182. PdfAfrica, Tanzaniadeposit - Igwisi Hills

Abstract: Pyroclastic deposits of the Holocene Igwisi Hills kimberlite volcanoes, Tanzania, preserve unequivocal evidence for rapid, syn-eruptive agglutination. The unusual pyroclasts are composed of ash-sized particles agglutinated to each other by thin necks. The textures suggest the magma was disrupted into droplets during ascent. Collisions between particles occurred within a volcanic plume and on deposition within the conduit to form a weakly agglutinated, porous pyroclastic deposit. Theoretical considerations indicate that agglutination occurred over short timescales. Agglutinated clasts were entrained into weak volcanic plumes and deposited around the craters. Our results support the notion that agglutination can occur during kimberlite eruptions, and that some coherent, dense rocks in ancient kimberlite pipes interpreted as intrusive rocks could instead represent agglutinated pyroclastic rocks. Differentiating between agglutinated pyroclastic rocks and effusive or intrusive rocks in kimberlite pipes is important because of the potential effects that pyroclastic processes might have on diamond concentrations in deposits.
DS202011-2040
2020
Haddock, D., Manya, S., Brown, R.J., Jones, T.J., Wadsworth, F.B., Dobson, K.J., Gernon, T.M.Syn-eruptive agglutination of kimberlite volcanic ash.Volcanica, 15p. PdfAfrica, Tanzaniadeposit - Igwisi Hills kimberlite

Abstract: Pyroclastic deposits of the Holocene Igwisi Hills kimberlite volcanoes, Tanzania, preserve unequivocal evidence for rapid, syn-eruptive agglutination. The unusual pyroclasts are composed of ash-sized particles agglutinated to each other by thin necks. The textures suggest the magma was disrupted into droplets during ascent. Collisions between particles occurred within a volcanic plume and on deposition within the conduit to form a weakly agglutinated, porous pyroclastic deposit. Theoretical considerations indicate that agglutination occurred over short timescales. Agglutinated clasts were entrained into weak volcanic plumes and deposited around the craters. Our results support the notion that agglutination can occur during kimberlite eruptions, and that some coherent, dense rocks in ancient kimberlite pipes interpreted as intrusive rocks could instead represent agglutinated pyroclastic rocks. Differentiating between agglutinated pyroclastic rocks and effusive or intrusive rocks in kimberlite pipes is important because of the potential effects that pyroclastic processes might have on diamond concentrations in deposits.
DS202012-2218
2020
Hainschwang, T., Notari, F., Pamies, G.The origin of 1330 nm center diamonds. ( hydrogen)Diamond and Related Materials, in press available, 19p. PdfGlobalspectroscopy

Abstract: This study covers hydrogen-rich fancy color diamonds that exhibit complex spectra from the UV all the way to the mid-IR. The diamonds with such spectra that are included here show a large range of colors from brownish yellow to brown, yellow-green to olive and gray to violet. The color origin of such diamonds has always been stated as “hydrogen-related”, without much evidence pointing towards hydrogen actually causing absorptions in the visible spectral range, but only based on their unusually high IR active hydrogen content determined via their FTIR spectra. The diamonds analyzed during this work always showed a series of absorptions in the near-infrared at 7495, 7850, 8255, and 8615 cm?1. For the first time, this here presented study shows the results of low temperature near-infrared spectroscopy performed for a series of differently colored diamonds that all showed these NIR absorptions. When measured at 77 K, it became clear that these NIR bands are actually part of an electronic optical center with ZPLs at 1329.8 to 1330.2 nm (7520-7518 cm?1)/1331.8 to 1332.2 nm (7508-7506 cm?1) and 1341 to 1341.2 nm (7457-7456 cm?1). In this paper we will refer to this defect as the "1330 nm center" (which corresponds to 7519 cm?1) for the sake of brevity. The detailed analysis of the spectra has demonstrated that the colors of diamonds that exhibit the 1330 nm center spectra are caused partially by this same center, and by complex absorption bands associated to two series of ZPLs represented by a number of sharp bands between 965 and 1001 nm, referred to as the 990 nm series in this study. Of these, the 990 nm series was found only in diamonds with significant IR active hydrogen concentrations, while the 1330 nm center was determined to be independent from the concentration of IR active hydrogen. The 1330 nm center was found in spectra lacking the 990 nm series of ZPLs, but the 990 nm series has never been found in spectra without the 1330 nm center. We are suggesting that the defects involved in these absorptions are all nickel?nitrogen-related, with the 1330 nm center lacking hydrogen while it seems reasonable to assume that the 990 nm series includes hydrogen in its structure.
DS202002-0192
2019
Hazarika, B., Malpe, D.B., Dongre, A.Petrology and geochemistry of a boninite dyke from the western Bastar craton of central India.Journal of Earth System Science, Vol. 128, 17p. PdfIndiaboninite

Abstract: The Dongargarh Supergroup along with the basal Amgaon Gneissic Complex constitutes the northwestern part of the central Indian Bastar craton. In the present study, we report a new finding of a boninite dyke intruded in the Amgaon gneisses of this area. The dyke composed of mainly pyroxenes, amphiboles and subordinate amount of plagioclase. The higher contents of SiO2 (51-54 wt.%), MgO (12-14 wt.%), Ni (375-473 ppm), Cr (1416-1580 ppm) and very low TiO2 (0.2-0.4 wt.%) are consistent with the boninite nature of the dyke as well as the unevolved primary nature of the source magma. The extraordinarily high CaO content (15.97-17.7 wt.%) with higher CaO/Al2O3 (3.13-3.96) ratios classifies it as high-Ca boninite. The trace element ratios including Zr/Ti, Ti/V, Ti/Sc and Ti/Yb further show its geochemical similarity with the Archaean boninite. The dyke also shows negative high-field strength element (Nb, Ta and Ti) anomalies which are the characteristics of the boninite rocks reported elsewhere and along with the enriched light rare earth element pattern, it shows more affinity particularly with the northern Bastar boninite dyke. The mineralogical and geochemical similarities of the boninite dykes from the Bastar craton indicate a widespread boninitic event during the Palaeoproterozoic having a similar origin. These boninite dykes indicate the preservation of subduction-related signatures in the lithospheric mantle beneath the Bastar craton at the time of its evolution or may be during the convergence of the Bastar and Bundelkhand cratons.
DS202003-0342
2020
Hazarika, B., Malpe, D.B., Dongre, A.Petrogenesis of mafic dykes from the western Bastar craton of central India and their relation to ourgrowth of Columbia supercontinent.Mineralogy and Petrology, in press available, 20p. PdfIndiacraton

Abstract: We report mineral compositions and bulk rock geochemistry of mafic dykes intruded in the western part of Bastar craton, comprising of Archaean Amgaon Group and Proterozoic Dongargarh Supergroup of rocks. Field relations show two distinct trends of these dykes which are almost perpendicular to each other but having similar mineralogical and geochemical characteristics. Dykes are mostly composed of pyroxenes, plagioclase and subordinate amount of amphiboles and Fe-Ti oxides (magnetite and ilmenite). These hypersthene normative basaltic dykes show tholeiitic trend and are characterised by narrow compositional variations of MgO (6.067.08 wt%), FeOt (15.0617.78 wt%), TiO2 (1.182.24 wt%), Al2O3 (11.9615.54 wt%) and low Mg# [atomic Mg/(Mg?+?Fe2+)?×?100] values in the range of 3748. Low loss on ignition (LOI) values <2 wt% and significant trends of trace elements (Nb, La, Th, Sr) with Zr indicate insignificant effects of post magmatic processes in these dykes. Smooth correlations between major oxides and MgO, among trace element ratios (Ce/La, Th/Yb, Nb/Yb) and negative Nb-Ta anomalies without positive Zr and Hf anomalies negate the crustal contamination effects. The correlations of compatible (e.g. Cr, Ni) and incompatible (e.g. Ba, Rb) elements show involvement of both fractional crystallisation and partial melting processes in their formation. Flat heavy rare earth element (HREE) pattern with low (Tb/Yb)n values reveal their genesis from a mantle source without involvement of garnet and geochemical models suggested in the present study indicate melting from spinel lherzolite mantle source. Strong geochemical similarities of present dykes with those of earlier reported Lakhna (1.46 Ga) and Bandimal (1.42 Ga) dykes of northern Bastar craton suggest a widespread mafic magmatic event across the Bastar craton during 1.421.46 Ga. Present dykes therefore represent a subduction related outgrowth of Columbia supercontinent due to the accretion of continental margins.
DS202007-1145
2020
Hecker, J.G., Marks, M.A.W., Wenzel, T., Markl, G.Halogens in amphibole and mica from mantle xenoliths: implications for the halogen distribution and halogen budget of the metasomatized continental lithosphere.American Mineralogist, Vol. 105, pp. 781-794.Mantlemetasomatism

Abstract: This study reports halogen contents (F and Cl) of amphibole and phlogopite derived from mantle xenoliths and one peridotite massif, for amphibole and phlogopite megacrysts and ultramafic magmatic cumulates (hornblendites) found in alkaline volcanic rocks from 12 localities in Europe and Africa. Amphibole and phlogopite contain more F than Cl with F/Cl ratios reaching about 160 in phlogopites and 50 in amphiboles. Phlogopites are higher in F (median of 3400 ?g/g) than amphibole (median of 1000 ?g/g), while median Cl contents are higher in amphibole (290 ?g/g) compared to phlogopite (180 ?g/g). The Cl contents and the F/Cl ratios in amphibole and phlogopite from mantle xenoliths exhibit large differences between samples of the same region, recording very large variations of halogen contents in the continental lithosphere. We suggest that the halogen content in such samples largely depends on the initial composition of percolating melts and fluids in the continental lithosphere. During reaction of these agents with peridotitic wall-rocks, Cl is preferentially retained in the fluid as it is much more incompatible compared to water and F. This desiccation effect continuously increases salinity (Cl content) and decreases the F/Cl ratio in the agent with time, causing variable Cl contents and F/Cl ratios in amphibole and phlogopite at a specific locality. Subsequent partial melting processes may then sequester and re-distribute, especially Cl among amphibole, phlogopite and melts/fluids as a result of its strong incompatibility, whereas F is much less affected as it behaves slightly compatible. The impact of even small amounts of amphibole and mica on the total halogen budget in the continental lithosphere is significant and both minerals can effectively contribute to the high halogen contents typical of alkaline melts.
DS202009-1630
2020
Hegner, E., Rajesh, S., Willbold, M., Muller, D., Joachimiski, M., Hofmann, M., Linnemann, U., Zieger, J., Pradeepkumar, A.P.Sediment derived origin of the putatative Munnar carbonatite, South India.Journal of Asian Earth Science, Vol. 200, 104432, 18p. PdfIndiadeposit - Munnar

Abstract: Metacarbonate assemblages in high-grade metamorphic terranes often pose challenges when trying to distinguish between mantle-derived carbonatite and sedimentary carbonate protoliths. We present a study of granulite-facies metacarbonate samples of the putative Munnar carbonatite described as decimeter-thick dikes and veins, and layers of a meter-thick metacarbonate and calc-silicate assemblage, respectively. Thin sections of the metacarbonate dike samples show absence of pyrochlore and ubiquitous scapolite, titanite, wollastonite, and detrital zircons are compatible with impure limestone protoliths. Nd and Sr isotope compositions indicate protoliths with Paleoproterozoic crustal residence times which contrast the mantle sources of Indian and global carbonatites. Trace-element patterns display the characteristics of upper crust, and Ce- and Y-anomalies in a number of samples suggest protolith formation under marine conditions. Carbon and oxygen isotope compositions of the metacarbonate samples interlayered with calc-silicate rocks are similar to those in marine limestone. The metacarbonate dikes, however, show mantle-like compositions which are interpreted as reflecting equilibration with mantle-derived CO2 during granulite-facies metamorphism. The dikes yielded a U-Pb zircon crystallization age of 1020 ± 70 Ma and a cross-cutting quartz syenite, thought to be cogenetic, a magmatic age of 620 ± 35 Ma; the hosting gneiss provided a magmatic age of 2452 ± 14 Ma. We conclude that the layered metacarbonate and calc-silicate rocks represent a former marine limestone and marl sequence and the metacarbonate dikes and veins small-volume melts of crust-derived carbonate-rich sediment.
DS202011-2041
2013
Henderson, B., Collins, A.S., Payne, J., Forbes, C., Saha, D.Geological and geochemistry constraining India in Columbia: the age, isotopic provenance and geochemistry of the protoliths of the Ongole Domain, southern eastern Ghats, India. *** NOTE DATEGondwana Research, in press available. 19p. PdfIndiaNuna

Abstract: The Ongole Domain in the southern Eastern Ghats Belt of India formed during the final stages of Columbia amalgamation at ca. 1600 Ma. Yet very little is known about the protolith ages, tectonic evolution or geographic affinity of the region. We present new detrital and igneous U-Pb-Hf zircon data and in-situ monazite data to further understand the tectonic evolution of this Columbia-forming orogen. Detrital zircon patterns from the metasedimentary rocks are dominated by major populations of Palaeoproterozoic grains (ca. 2460, 2320, 2260, 2200-2100, 2080-2010, 1980-1920, 1850 and 1750 Ma), and minor Archaean grains (ca. 2850, 2740, 2600 and 2550 Ma). Combined U-Pb ages and Lu-Hf zircon isotopic data suggest that the sedimentary protoliths were not sourced from the adjacent Dharwar Craton. Instead they were likely derived from East Antarctica, possibly the same source as parts of Proterozoic Australia. Magmatism occurred episodically between 1.64 and 1.57 Ga in the Ongole Domain, forming felsic orthopyroxene-bearing granitoids. Isotopically, the granitoids are evolved, producing ?Hf values between ? 2 and ? 12. The magmatism is interpreted to have been derived from the reworking of Archaean crust with only a minor juvenile input. Metamorphism between 1.68 and 1.60 Ga resulted in the partial to complete resetting of detrital zircon grains, as well as the growth of new metamorphic zircon at 1.67 and 1.63 Ga. In-situ monazite geochronology indicates metamorphism occurred between 1.68 and 1.59 Ga. The Ongole Domain is interpreted to represent part of an exotic terrane, which was transferred to proto-India in the late Palaeoproterozoic as part of a linear accretionary orogenic belt that may also have included south-west Baltica and south-eastern Laurentia. Given the isotopic, geological and geochemical similarities, the proposed exotic terrane is interpreted to be an extension of the Napier Complex, Antarctica, and may also have been connected to Proterozoic Australia (North Australian Craton and Gawler Craton).
DS202007-1146
2020
Heyn. B.H., Conrad, C.P., Tronnes, R.G.Core-mantle boundary topography and its relation to the viscosity structure of the lowermost mantle.Earth and Planetary Science Letters, Vol. 543, 116358 14p. PdfMantlemantle plumes

Abstract: Two large areas of anomalously low seismic velocities are visible in all tomographic models of the lowermost mantle. Depending on the density structure of these Large Low Shear Velocity Provinces (LLSVPs), the core-mantle boundary (CMB) will deform upwards or downwards due to isostatic and dynamic topography, the latter being sensitive to the viscosity structure of the lowermost mantle. Heterogeneities in the viscosity structure, although difficult to constrain, might be especially important if the LLSVPs are thermochemical piles with elevated intrinsic viscosity as suggested by mineral physics. Based on numerical models, we identify a short-wavelength (about 80-120 km wide, up to a few km deep) topographic depression that forms around the pile edges if the pile is more viscous than the surrounding mantle. The depression forms when a wedge of thermal boundary layer material becomes compressed against the viscous pile, and is enhanced by relative uplift of the CMB beneath the pile by plumes rising above it. The depth and asymmetry of the depression constrain the magnitude of the viscosity contrast between pile and the surrounding mantle. Furthermore, (periodic) plume initiation and pile collapse at the pile margin systematically modify the characteristic depression, with a maximum in asymmetry and depth at the time of plume initiation. Core-reflected waves or scattered energy may be used to detect this topographic signature of stiff thermochemical piles at the base of the mantle.
DS202011-2042
2020
Hilson, G.The African mining vision: a manifesto for more inclusive extractive industry-led developments.Canadian Journal of Development Studies, Vol. 41, 3, pp. 417-431. pdfAfricalegal

Abstract: This paper introduces a special section of the Canadian Journal of Development Studies, "The Africa Mining Vision: A Manifesto for More Inclusive Extractive Industry-Led Development?" Conceived by African ministers "in charge of mineral resources" with inputs and guidance from African Union Heads of State, the Africa Mining Vision (AMV) was officially launched in February 2009. The papers presented in this special section reflect critically on progress that has since been made with operationalising the AMV at the country level across Africa; the general shortcomings of the manifesto; and the challenges that must be overcome if the continent is to derive greater economic benefit from its abundant mineral wealth.
DS202005-0736
2020
Hinze, W. J,, Chandler, V.W.Reviewing the configuration and extent of the Midcontinent rift system.Precambrian Research, Vol. 342, 18p. PdfUnited States, Michigan, Ohio, Oklahomageophsyics - magnetics

Abstract: Uncertainty exists in the configuration and extent of the Midcontinent Rift System (MRS) because of deficiencies in geophysical data and limited information from outcrops and basement drill holes. Additional ambiguity is caused by misunderstanding the definition of continental rifts. Six principal problematic regions in mapping the MRS are described. Gravity and magnetic data, supported by drill hole and seismic reflection data, show that the Eastern Lake Superior rift segment of the MRS continues south from Lake Superior and connects to a much narrower rift in northern Lake Michigan. The eastern margin of this transition is ill defined because of the lack of definitive anomalies and supporting seismic and drill hole data, but is interpreted to occur near the U.S. - Canada border. The rift segment in southeastern Michigan intersects the Grenville Front and likely continues eastwards in modified form to near the boundary with Canada. Cross-cutting gravity and magnetic signatures may reflect Grenvillian overthrusts near the terminus of the MRS in Michigan. The proposed southerly extensions of both branches of the rift system into Oklahoma and Ohio are based primarily on positive gravity anomalies, but neither postulated extension appears to be associated with rifted troughs. Rather the gravity anomalies of the western branch are related to intrusive mafic rocks and those of the eastern branch are most likely related to deep crustal metamorphic rocks thrust into juxtaposition with less dense crust by Grenville orogenesis. Recent paleomagnetic investigations, in conjunction with high-resolution radiometric dating, imply that the MRS developed during the rapid southward movement of Laurentia during a quiescent period along its eastern continental margin. Massive magmatic activity accompanying the rifting was likely due to rising mantle material that was displaced by subducted lithosphere along the southern margin. The heated crust was made more ductile, fostering rifting due to extensional stresses. The Nipigon Embayment remains as a possible candidate for an early "third branch" of the MRS, but current evidence is insufficient to include the Fort Wayne "rift" as part of the MRS. Future studies of the MRS would be well-served by new age-dating and high-resolution seismic studies of the lithosphere.
DS202001-0015
2018
Hodder, T. Kelley, S.E.Kimberlite indicator minerals and clast lithology composition of till, Kaskattama region northeastern Manitoba (parts of NTS 53N, O, 54 B,C.)Manitoba Report, GS2018-13 pdf 17p. Canada, Manitobageochemistry

Abstract: Canada exhibits many of the challenges involved with exploring for coloured stones in countries with very low population densities, temperate-to-arctic climates and a lack of infrastructure hindering access to most prospective areas. Despite this, a number of discoveries have occurred, mainly during the past two decades. These include emeralds from Northwest Territories (1997) and Yukon (1998); sapphire (2002) and spinel (from 1982)—including cobalt-blue stones—from Baffin Island in Nunavut; and ruby and pink sapphire (2002) from British Columbia. Such discoveries can be assisted by undertaking scientific research into gem formation, as well as by applying exploration criteria developed elsewhere to uncharted territory. Future exploration in Canada and other countries facing similar challenges will likely benefit from additional geological studies to identify prospective areas and features; innovative means of transportation, such as boats instead of aircraft; drones for exploring rugged terrain; hyperspectral imaging for mineral sensing; surveying with UV lamps to identify minerals associated with gem mineralisation; and careful prospecting (including field mapping and collecting heavy mineral concentrates) by experienced individuals. Quaternary geology fieldwork was conducted at a reconnaissance-scale in the Kaskattama highland area to document the Quaternary stratigraphy and till composition. The diamond potential of this region was investigated using kimberlite-indicator-mineral (KIM) counts from till samples. Indicator mineral results are the focus of this report and are combined with ice-flow and till-clast-lithology data to provide a context to interpret provenance. Kimberlite-indicator minerals were recovered from glacial sediments (till) in the Kaskattama highland area and KIM counts are elevated relative to data from the surrounding area. The lowest KIM counts were from till with a high Hudson Bay Basin (carbonatedominated) and low undifferentiated greenstone and greywacke (UGG) provenance signature. The highest KIM counts are associated with till samples that have a relatively elevated UGG or elevated granitoid provenance signature. Till samples with relatively elevated UGG concentration have an interpreted east or southeast provenance, which is supported by ice-flow data and the recovery of distinct east-sourced erratics. Till samples with a relatively elevated granitoid clast concentration have a correlation with the southwest- trending Hayes streamlined-landform flowset. Considering the likely provenance for granitoid clasts is to the northwest, the presence of relatively high concentrations of granitoid clasts in the Hayes flowset could be indicative of a higher inheritance from previous ice-flow events or a palimpsest dispersal pattern. Interpretation of till-composition and ice-flow data has indicated there are likely multiple sources for the KIMs recovered during this study. Detailed work is recommended to clarify local-scale dispersal patterns.
DS202005-0737
2019
Hoffman, P.F.Big Time: Proterozoic Eon.Annual Review of Earth and Planetary Sciences, Vol. 47, pp. 1-17. pdfMantleplate tectonics

Abstract: The Proterozoic Eon was once regarded as the neglected middle half of Earth history. The name refers to early animals, but they did not appear until the eon (2.5-0.54 Ga) was nearly over. Eukaryotic cells and sexual reproduction evolved much earlier in the eon, as did chloroplasts. Molecular dioxygen, the presence of which altered the geochemical behavior of nearly every element essential to life, rose from negligible to near-modern levels, and then plummeted before rising fitfully again. Plate tectonics took on a modern form, and two supercontinents, Nuna and Rodinia, successively congregated and later dispersed. Climate regulatory failures, i.e., Snowball Earth, appear to be a uniquely Proterozoic phenomenon, having occurred twice in rapid succession near the end of the eon (from 717 to 660 Ma and from 650 to 635 Ma) and arguably once near its beginning (ca. 2.43 Ga). Dynamic sea glaciers covered Snowball Earth oceans from pole to pole, and equatorial sublimation drove slow-moving ice sheets on land. Ultimately, the gradual accumulation of CO2 triggered rapid deglaciation and transient greenhouse aftermaths. Physically based and geologically tested, Neoproterozoic Snowball Earth appears to have molecular legacies in ancient bitumens and modern organisms. This is the story of my love affair with an eon that is now a little less neglected.
DS202008-1400
2020
Hoggard, M.J., Czarnota, K., Richards, F.D., Huston, D.L., Jaques, A.L., Ghelichkhan, S.Global distribution of sediment hosted metals controlled by craton edge stability. ( not specific to diamonds but of interest)Nature Geoscience, Vol. 13, pp. 504-510.Mantlelithospheric thickness

Abstract: Sustainable development and the transition to a clean-energy economy drives ever-increasing demand for base metals, substantially outstripping the discovery rate of new deposits and necessitating dramatic improvements in exploration success. Rifting of the continents has formed widespread sedimentary basins, some of which contain large quantities of copper, lead and zinc. Despite over a century of research, the geological structure responsible for the spatial distribution of such fertile regions remains enigmatic. Here, we use statistical tests to compare deposit locations with new maps of lithospheric thickness, which outline the base of tectonic plates. We find that 85% of sediment-hosted base metals, including all giant deposits (>10?megatonnes of metal), occur within 200?kilometres of the transition between thick and thin lithosphere. Rifting in this setting produces greater subsidence and lower basal heat flow, enlarging the depth extent of hydrothermal circulation available for forming giant deposits. Given that mineralization ages span the past two?billion?years, this observation implies long-term lithospheric edge stability and a genetic link between deep Earth processes and near-surface hydrothermal mineral systems. This discovery provides an unprecedented global framework for identifying fertile regions for targeted mineral exploration, reducing the search space for new deposits by two-thirds on this lithospheric thickness criterion alone.
DS202007-1147
2020
Hoggard, M.J., Parnell-Turner, R., White, N. Hotspots and mantle plumes revisited: towards reconciling the mantle heat transfer discrepancy.Earth and Planetary Science Letters, Vol. 542, 116317 16p. PdfMantleplumes, geothermometry

Abstract: Mantle convection is the principal mechanism by which heat is transferred from the deep Earth to the surface. Cold subducting slabs sink into the mantle and steadily warm, whilst upwelling plumes carry heat to the base of lithospheric plates where it can subsequently escape by conduction. Accurate estimation of the total heat carried by these plumes is important for understanding geodynamic processes and Earth's thermal budget. Existing estimates, based upon swell geometries and velocities of overriding plates, yield a global heat flux of ?2 TW and indicate that plumes play only a minor role in heat transfer. Here, we revisit the Icelandic and Hawaiian plumes to show that their individual flux estimates are likely to be incorrect due to the assumption that buoyancy is mainly produced within the lithosphere and therefore translates at plate velocities. We develop an alternative methodology that depends upon swell volume, is independent of plate velocities, and allows both for decay of buoyancy through time and for differential motion between asthenospheric buoyancy and the overlying plate. Reanalysis of the Icelandic and Hawaiian swells yields buoyancy fluxes of Mg s?1 and Mg s?1, respectively. Both swells are used to calibrate a buoyancy decay timescale of ?45 Myr for the new volumetric approach, which enables buoyancy fluxes to be estimated for a global inventory of 53 swells. Estimates from magmatic hotspots yield a cumulative lower bound on global plume flux of 2 TW, which increases to 6 TW if amagmatic swells are also included and if all buoyancy is assumed to be thermal in origin. Our results suggest that upwelling plumes play a significant role in the transfer of heat into the uppermost mantle.
DS202001-0016
2019
Holwell, D.A., Fiorentini, M., McDonald, I., Lu, Y., Giuliani, A., Smith, D.J., Keith, M., Locmelis, M.A metasomatized lithospheric mantle control on the metallogenic signature of post-subduction magmatism. ( Not specific to diamonds)Nature Communications, doi.org/10.1038/s41467-019-11065-4 pdf 10p.Mantlesubduction

Abstract: Ore deposits are loci on Earth where energy and mass flux are greatly enhanced and focussed, acting as magnifying lenses into metal transport, fractionation and concentration mechanisms through the lithosphere. Here we show that the metallogenic architecture of the lithosphere is illuminated by the geochemical signatures of metasomatised mantle rocks and post-subduction magmatic-hydrothermal mineral systems. Our data reveal that anomalously gold and tellurium rich magmatic sulfides in mantle-derived magmas emplaced in the lower crust share a common metallogenic signature with upper crustal porphyry-epithermal ore systems. We propose that a trans-lithospheric continuum exists whereby post-subduction magmas transporting metal-rich sulfide cargoes play a fundamental role in fluxing metals into the crust from metasomatised lithospheric mantle. Therefore, ore deposits are not merely associated with isolated zones where serendipitous happenstance has produced mineralisation. Rather, they are depositional points along the mantle-to-upper crust pathway of magmas and hydrothermal fluids, synthesising the concentrated metallogenic budget available.
DS202006-0922
2020
Hong, L., Znag,, M.Object oriented multiscale deep features for hyperspectral image classification. (Not specific to diamonds)International Journal of Remote Sensing, Vol. 41, 14, pp. 5549-5572.Globalhyperspectral

Abstract: The classification of hyperspectral images (HSIs) is one of the most popular topics in the remote sensing community. Numerous feature extraction methods have been proposed to improve the classification accuracy of HSIs. Recently, deep features extracted by convolution neural network (CNN) have been introduced into the classification process of HSIs. Due to the nonlinear and invariant advantages of the features, CNN methods provide a powerful tool for representing geographic objects and classifying HSIs. However, traditional deep features only extracted at pixel-level and often neglect multiscale characteristics of geographic objects. In this study, a new deep feature extraction method is proposed, which takes advantage of multi-scale object analysis and the CNN model. Firstly, multiscale image objects are obtained by the multiscale segmentation algorithm and multiscale low-level features of objects are extracted. Secondly, the CNN is devoted to obtain deep features from low-level object features at each scale, respectively. Thirdly, the obtained deep features at all scales are stacked and fed to one fully connected layer to extract the multiscale deep learning features for classification. Finally, the logistic regression classifier is applied to hyperspectral image (HSI) classification based on object-oriented multiscale deep features. The proposed method was carried out on three widely used hyperspectral data sets: University of Pavia, Salinas, and Washington DC. The results reveal that the proposed method provides better results than other state-of-the-art methods.
DS202012-2219
2020
Hoover, W.F., Page, F.Z., Schulze, D.J., Kitajima, K., Valley, J.W.Massive fluid influx beneath the Colorado Plateau ( USA) related to slab removal and diatreme emplacement: evidence from oxygen isotope zoning in eclogite xenoliths.Journal of Petrology, in press available, 52p. PdfUnited States, Colorado Plateaueclogite

Abstract: The Colorado Plateau has undergone as much as 1.8?km of uplift over the past 80?Ma, but never underwent the pervasive deformation common in the neighboring tectonic provinces of the western USA. To understand the source, timing and distribution of mantle hydration, and its role in plateau uplift, garnets from four eclogite xenoliths of the Moses Rock diatreme (Navajo Volcanic Field, Utah, USA) were analyzed in situ for ?18O by secondary ion mass spectrometry. These garnets have the largest reported intra-crystalline oxygen isotope zoning to date in mantle-derived xenoliths with core-to-rim variations of as much as 3‰. All samples have core ?18O values greater than that of the pristine mantle (?5.3‰, mantle garnet as derived from mantle zircon; Valley et al., 1998; Page et al., 2007) consistent with an altered upper oceanic crust protolith. Oxygen isotope ratios decrease from core to rim recording interaction with a low-?18O fluid at high temperature, likely derived from serpentinite in the foundering Farallon slab. All zoned samples converge at a ?18O value of ?6‰, regardless of core composition, suggesting that fluid infiltration was widely distributed. Constraints on the timing of this fluid influx, relative to diatreme emplacement, can be gained from diffusion modeling of major element zoning in garnet. Modeling using best-estimates of peak metamorphic conditions (620ºC, 3.7?GPa) yield durations of?
DS202011-2043
2019
Horvath, L., Gault, R.A., Pfenninger-Horvath, Poirier, G.Mont Saint-Hilaire: history, geology, mineralogy.The Canadian Mineralogist, Special Publication 14, 634p. Canada, QuebecBook

Abstract: This paper introduces a special section of the Canadian Journal of Development Studies, "The Africa Mining Vision: A Manifesto for More Inclusive Extractive Industry-Led Development?" Conceived by African ministers "in charge of mineral resources" with inputs and guidance from African Union Heads of State, the Africa Mining Vision (AMV) was officially launched in February 2009. The papers presented in this special section reflect critically on progress that has since been made with operationalising the AMV at the country level across Africa; the general shortcomings of the manifesto; and the challenges that must be overcome if the continent is to derive g Taking over 20 years of meticulous preparation, László and Elsa Horváth, a duo of dedicated and dynamic amateur mineralogists, along with two researchers, Robert Gault, a mineralogist, and Glenn Poirier, a geologist, have produced the ultimate book "Mont Saint-Hilaire: History, Geology, Mineralogy". The photography captures the colors of Vásárely, the symmetry of Escher, the form of Bartók and the intricate patterns of Mandelbrot, all found here, in this miracle of nature. One cannot but marvel at how this single, small quarry contains such mineral diversity. At last count, over 434 mineral species have been found at Mont Saint-Hilaire, representing 9% of all known mineral species. The 66 type minerals first described from this locality represent 1.3 % of all mineral species, placing the Poudrette quarry in an extremely rarified class for worldwide mineral localities. Almost half, 47, of all known chemical elements are included in this mineral mix. Beginning some 124 million years ago, several million years and a variety of geological processes were needed to accomplish this assemblage. Be captivated, learn and, most of all, enjoy!reater economic benefit from its abundant mineral wealth.
DS202011-2044
2020
Hou, X-Z., Yang, Z-F., Wang, Z-J.The occurrence characteristics and recovery potential of middle-heavy rare earth elements in the Bayan Obo deposit, northern China.Ore Geology Reviews, Vol. 126, 103737, 13p. PdfChinaREE

Abstract: The Bayan Obo deposit is a world-class Fe-REE-Nb deposit, and its reserves of rare earth element (REE) resources rank the first over the world. In the face of the current situation of insufficient utilization rate of rare earth resources and scarcity of middle-heavy rare earth elements (M?HREE) resources, the Bayan Obo deposit with such a huge amount of M?HREE cannot be underestimated. In this paper, the occurrence characteristics of M?HREE in different types of iron ore in the Bayan Obo main ore body are studied by using field emission scanning electron microscope (FESEM), energy dispersive spectrometer (EDS) and advanced mineral identification and characterisation system (AMICS), and the enrichment mechanism is also discussed. The results show that both Sm and Y are the most abundant M?HREE in each type of iron ore in the main ore body, and the content of M?HREE accounts for 1.41%-5.57% of total REE, among which the content of M?HREE in aegirine type Nb-REE-Fe ore (824.47 ppm) and fluorite type Nb-REE-Fe ore (794.82 ppm) are higher, and the content of M?HREE in massive type Nb-REE-Fe ore is lower (318.49 ppm). The main minerals containing M?HREE are bastnasite, parisite, Huanghoite, monazite, aeschynite and fergusonite, among which the content of M?HREE in fergusonite and aeschynite are the highest. According to the characteristics of mineral paragenetic association of REE in this ore district, it is believed that the REE migrates mainly in many different forms of complexes. Heavy rare earth elements (HREE) mainly experienced carbonatite magmatism stage, sodium-fluorine metasomatism stage and late vein mineralization stage, and finally got enrichment.
DS202012-2220
2020
Howarth, G.What meteorites can tell us about Mars.Univ. Cape Town, https://www.news.uct.ac.za /news/research-office/ -article/2020-11-24-what -meteorites-can-tell- us-about-marsMarsmeteorites

Abstract: Hundreds of millions of years ago something crashed into the planet Mars with enough force to eject pieces of Martian rock into space. Some of these pieces of rock made their way to Earth where they entered our atmosphere as meteors. A precious few landed on the surface of our planet as meteorites. Thanks to scientists like Geoffrey Howarth, a geologist based at the University of Cape Town (UCT), these Martian meteorites are now being studied to better understand the structure and geological history of the red planet. Here’s what we know so far.
DS202004-0518
2020
Howarth, G.H., Giuliani, A.Contrasting types of miceaceous kimberlite-lamproite magmatism from the Man craton ( West Africa): new insights from petrography and mineral chemistry.Lithos, in press available 63p. PdfAfrica, Sierra Leone, Liberiadeposit - Tongo, Weasua

Abstract: Diamondiferous rock types worldwide are broadly divided into kimberlite and lamproite, the latter of which have unique characteristics in different regions and include carbonate-rich varieties (formerly orangeites/Group II kimberlites). Diamondiferous rocks in West Africa are typically micaceous and share petrographic, mineralogical, and geochemical characteristics with both kimberlites and lamproites. To further constrain the classification and petrogenesis of diamondiferous rocks worldwide and their variability between different cratonic regions, in this study we combine detailed petrographic observations with olivine, phlogopite, and spinel chemistry for hypabyssal samples from the Jurassic Tongo dike (Sierra Leone) and the Neoproterozoic Weasua cluster (Liberia). The Tongo dike contains macrocrysts of olivine and phlogopite in a groundmass of olivine, abundant phlogopite, spinel, perovskite, and apatite with a base of calcite, dolomite, and lesser serpentine. The phlogopite is characterised by concurrent FeO and Al2O3 enrichment, which is typical of kimberlites and unlike lamproites. These features and the kimberlite-like spinel compositions allow us to classify the Tongo samples as micaceous kimberlites. The Weasua rocks comprise macrocrysts of olivine in a groundmass of olivine, phlogopite, diopside (zoned towards aegirine-rich rims), spinel, perovskite, and apatite with a base of serpentine and less common calcite. The composition of Weasua phlogopite trends to significant FeO enrichment and Al2O3 depletion, i.e. towards tetraferriphlogopite. The enrichment in mica, phlogopite chemistry and presence of magmatic diopside indicates that these rocks are olivine lamproites. The populations of olivine macrocrysts and microcrysts at Tongo and Weasua are similar and characterised by distinct core and rim zones. Two distinct olivine core populations are observed. 1) forsterite-rich (Fo?>?90) olivine interpreted to reflect xenocrysts from typical mantle peridotites. Al-in-olivine thermometry suggests that these cores have P-T equilibration within diamond stability at Weasua and Tongo. 2) Al-, Ca- and Na- rich cores with P-T formation conditions extending beyond the mantle adiabat. These cores are interpreted to reflect metasomatic and thermal perturbation linked with the infiltration of kimberlite/lamproite melts in the deep lithosphere shortly before entrainment in the ascending magma. The olivine rims at Tongo and Weasua show limited variations in Fo contents at similar values of 88.9?±?0.8 for Tongo and 89.6?±?1.2 for Weasua, as well as similar minor and trace element concentrations. Thus, whereas the Tongo and Weasua rock types are classified as kimberlite and olivine lamproite, respectively, the olivine chemistry suggests a similar petrogenetic evolution.
DS202006-0923
2020
Howell, D., Collins, A.T., Loudin, L.C., Diggle, P.L., D'Haenens-Johansson, U.F.S., Smit, K.V., Katrusha, A.N., Butler, J.E., Nestola, F.Automated FTIR mapping of boron distribution in diamond. DiaMap_IIb ( synthetics)Diamonds & Related Materials, In press available, 30p. PdfGlobalsynthetics

Abstract: Type IIb diamonds are those that contain more boron than nitrogen. The presence of this uncompensated boron gives rise to absorption in the infrared part of the electromagnetic spectrum, extending into the visible region and often resulting in blue colouration. Here we report on the expansion of the DiaMap freeware (for the automated spectral deconvolution of Type I [nitrogen containing] diamonds) to work on Type IIb diamonds, returning concentrations from three boron-related absorption bands, and determining which band provides the most reliable value. The program uses the calibration coefficients of Collins (2010), which show good relative agreement between the three bands, but might require some further study to confirm their absolute accuracy to the uncompensated boron concentration. The methodology of DiaMap_IIb is applicable to all Type IIb diamonds, both natural and synthetic. Analysis of high-resolution Fourier-transform infrared (FTIR) maps of two high-pressure high-temperature (HPHT) synthetic diamonds using DiaMap_IIb, confirm the growth sector dependence of the boron incorporation. Partitioning of boron strongly favours the octahedral {111} sectors.
DS202004-0519
2020
Howell, D., Stachel, T., Stern, R.A., Pearson, D.G., Nestola, F., Hardman, M.F., Harris, J.W., Jaques, A.L., Shirery, S.B., Cartigny, P., Smit, K.V., Aulbach, S., Brenker, F.E., Jacob, D.E., Thomassot, E., Walter, M.J., Navon, O.Deep carbon through time: Earth's diamond record and its implications for carbon cycling and fluid speciation in the mantle.(peridotite and eclogite used)Geochimica et Cosmochimica Acta, Vol. 275, pp. 99-122.Mantlecarbon

Abstract: Diamonds are unrivalled in their ability to record the mantle carbon cycle and mantle fO2 over a vast portion of Earth’s history. Diamonds’ inertness and antiquity means their carbon isotopic characteristics directly reflect their growth environment within the mantle as far back as ?3.5 Ga. This paper reports the results of a thorough secondary ion mass spectrometry (SIMS) carbon isotope and nitrogen concentration study, carried out on fragments of 144 diamond samples from various locations, from ?3.5 to 1.4 Ga for P [peridotitic]-type diamonds and 3.0 to 1.0 Ga for E [eclogitic]-type diamonds. The majority of the studied samples were from diamonds used to establish formation ages and thus provide a direct connection between the carbon isotope values, nitrogen contents and the formation ages. In total, 908 carbon isotope and nitrogen concentration measurements were obtained. The total ?¹³C data range from ?17.1 to ?1.9 ‰ (P = ?8.4 to ?1.9 ‰; E = ?17.1 to ?2.1‰) and N contents range from 0 to 3073 at. ppm (P = 0 to 3073 at. ppm; E = 1 to 2661 at. ppm). In general, there is no systematic variation with time in the mantle carbon isotope record since > 3 Ga. The mode in ?¹³C of peridotitic diamonds has been at ?5 (±2) ‰ since the earliest diamond growth ?3.5 Ga, and this mode is also observed in the eclogitic diamond record since ?3 Ga. The skewness of eclogitic diamonds’ ?¹³C distributions to more negative values, which the data establishes began around 3 Ga, is also consistent through time, with no global trends apparent. No isotopic and concentration trends were recorded within individual samples, indicating that, firstly, closed system fractionation trends are rare. This implies that diamonds typically grow in systems with high excess of carbon in the fluid (i.e. relative to the mass of the growing diamond). Any minerals included into diamond during the growth process are more likely to be isotopically reset at the time of diamond formation, meaning inclusion ages would be representative of the diamond growth event irrespective of whether they are syngenetic or protogenetic. Secondly, the lack of significant variation seen in the peridotitic diamonds studied is in keeping with modeling of Rayleigh isotopic fractionation in multicomponent systems (RIFMS) during isochemical diamond precipitation in harzburgitic mantle. The RIFMS model not only showed that in water-maximum fluids at constant depths along a geotherm, fractionation can only account for variations of <1‰, but also that the principal ?¹³C mode of ?5 ± 1‰ in the global harzburgitic diamond record occurs if the variation in fO2 is only 0.4 log units. Due to the wide age distribution of P-type diamonds, this leads to the conclusion that the speciation and oxygen fugacity of diamond forming fluids has been relatively consistent. The deep mantle has therefore generated fluids with near constant carbon speciation for 3.5 Ga.
DS202001-0017
2019
Huang, C., Zhang, N, Li, Z.X., Dang, Z.Modeling the inception of supercontinent breakup: stress state and the importance of orogens.Geochemistry, Geophysics, Geosystems, in press available pdf 20p.Globalgeodynamics

Abstract: The relative significance of various geodynamic mechanisms that drive supercontinent breakup is unclear. A previous analysis of extensional stress during supercontinent breakup demonstrated the importance of the plume?push force relative to the dragging force of subduction retreat. Here, we extend the analysis to basal traction (shear stress) and cross?lithosphere integrations of both extensional and shear stresses, aiming to understand more clearly the relevant importance of these mechanisms in supercontinent breakup. More importantly, we evaluate the effect of preexisting orogens (mobile belts) in the lithosphere on supercontinent breakup process. Our analysis suggests that a homogeneous supercontinent has extensional stress of 20-50 MPa in its interior (<40° from the central point). When orogens are introduced, the extensional stress in the continents focuses on the top 80?km of the lithosphere with an average magnitude of ~160 MPa, whereas at the margin of the supercontinent the extensional stress is 5-50 MPa. In both homogeneous and orogeny?embedded cases, the subsupercontinent mantle upwellings act as the controlling factor on the normal stress field in the supercontinent interior. Compared with the extensional stress, shear stress at the bottom of the supercontinent is 1-2 order of magnitude smaller (0-5 MPa). In our two end?member models, the breakup of a supercontinent with orogens can be achieved after the first extensional stress surge, whereas for a hypothetical supercontinent without orogens it starts with more diffused local thinning of the continental lithospheric before the breakup, suggesting that weak orogens play a critical role in the dispersal of supercontinents.
DS202007-1148
2020
Huang, F., Sverjensky, D.A.Mixing of carbonatitic into saline fluid fluid during Panda diamond formation.Geochimica et Cosmochimica Acta, in press available 59p. PdfCanada, Northwest Territoriesdeposit - Panda

Abstract: Diamonds containing fluid inclusions provide invaluable samples of upper mantle fluids, the study of which illuminates not only diamond formation but also the long-term evolution of the subcratonic, lithospheric mantle. The very large range of inclusion compositions worldwide has been interpreted to represent four end-member fluids: saline (rich in Na+K+Cl); silicic (rich in Si+Al); and carbonatitic (rich in Ca+Mg+Fe, with low-Mg and high-Mg end members). However, the sources and evolution of these fluids and the processes involved in diamond formation are still unclear. We used an unusual study of diamonds from the Panda kimberlite (Ekati Mine, Northwest Territories, Canada) in which both mineral and fluid inclusions in the diamonds were analyzed (Tomlinson et al., 2006) to develop models of the saline, silicic, and low-Mg carbonatitic fluids present in the Panda fluid inclusions. The models used aqueous speciation and solubility calculations to link the solid and fluid inclusion chemistry with model upper mantle rock types. We used the extended Deep Earth Water model to calculate equilibrium constants previously calibrated with experimental rock solubilities referring to upper mantle temperatures and pressures (Huang and Sverjensky, 2019). Our results at 950 °C and 4.5 GPa suggest that the saline fluid could originate from peridotite, the silicic fluid from eclogite, and the low-Mg carbonatitic fluid from carbonated dunite. The fluid models were then used to predict the irreversible, chemical mass transfer when the carbonatitic fluid infiltrated a harzburgite containing a saline fluid. Simultaneous reduction of formate and bicarbonate in the carbonatitic fluid and oxidation of aqueous hydrocarbons from the peridotitic fluid during mixing and reaction with harzburgite resulted in the formation of diamond, olivine, garnet, and clinopyroxene, and increases in the and . Olivine was predicted to become more Fe-rich and garnet more Ca and Fe-rich with reaction progress, in agreement with reported temporal trends (core-to-rim) in the Panda mineral inclusions. The fluid at the site of diamond formation became more saline with reaction progress and the predicted aqueous phase concentrations of all elements changed consistent with trends in Panda fluid inclusions. In contrast, a prediction for a saline fluid infiltrating a harzburgite containing a carbonatitic fluid resulted in trends of the silicate minerals and the salinity with reaction progress that were in the opposite direction to data from the Panda diamonds. Overall, our study strongly supports the notion that fluids from subducting slabs could mix and precipitate diamonds containing carbon from both oxidized and reduced sources, while adding Ca and Fe to the sub-lithospheric cratonic mantle through metasomatic reactions.
DS202008-1401
2020
Huang, S., Tschauner, O., Yang, S., Humayun, M.HIMU signature trapped in a diamond from the mantle transition zone.Goldschmidt 2020, 1p. AbstractMantlediamond inclusion

Abstract: Mantle plumes sample the deep mantle. A limited number of geochemical endmember components can describe the isotopic and compositional variations in the ocean island basalts (OIBs), which are produced by plume volcanism. The endmembers are correlated to compositions in the OIB source regions or represent incorporation of material upon ascent. However, their actual nature and origins are still highly debated. The depths of plume sources have been proposed to be anywhere between the core-mantle boundary and the upper mantle, and need not be the same for all plume-related volcanic activities. Using a combination of synchrotron micro-X ray fluorescence and -diffraction mapping, and in-situ Laser Ablation Inductively Coupled Plasma Mass Spectrometry, we show that the elemental features of HIMU-rich OIBs, such as Bermuda, St Helena, and Cook-Austral, exactly match the geochemical signature of a multiphase inclusion in a diamond. The geochemical signature in our studied diamond inclusion is markedly different from that of inclusions in lithospheric diamonds. The phases identified in the inclusion are majorite-rich garnet, ilmenite, the sodic 10Å-phase (TAP), and liebermannite. Furthermore, we show that this inclusion was entrapped at 14.5 ± 0.5 GPa (420-440 km) and 1450 ± 50 K. At the conditions of entrapment, the diamond inclusion phase assembly was garnet + ilmenite + liebermannite + clinopyroxene + stishovite + fluid. Sodic TAP is a retrograde product of reaction between clinopyroxene, stishovite, and fluid upon ascent. Its presence shows that the HIMU source is water-saturated. Entrapment in diamond indicates that the fluid also contained carbonate. The conditions of 14.5 ± 0.5 GPa and 1450 ± 50 K plot right on top of the alkaline carbonatite solidus, and match the formation of carbonatitic melt from subducted slabs plus diamond formation from reaction of carbonate with iron. In summary, our data show that the transition zone source accounts for the global HIMU endmember.
DS202001-0018
2019
Huang, W., Ni, P., Shui, T., Shi, G.Hydrogen rich green diamond color treated by multi step processing.Gems & Gemology, Vol. 55, 3, pp. 398-405.Globaldiamond color

Abstract: A cut diamond of intense yellowish green color has been characterized using microscopy and spectroscopic techniques. The diamond has been unambiguously identified as color-treated. The simultaneous presence of multiple centers related to irradiation and annealing—including H1a, H1b, NV0, NV-, H3, H4, GR1, and H2—was revealed. UV-Vis-NIR absorption spectroscopy showed that the diamond owes its color to the two major bands related to H3 and GR1. The combination of these spectroscopic features in one diamond has not been reported in the gemological literature, suggesting that this diamond was subjected to a complex treatment procedure that is not frequently applied. Taking into account the thermal stability of the defects involved and the defect transformations at high temperatures, two possible treatment procedures explaining the observed combination of spectroscopic features are proposed.
DS202001-0019
2019
Huang, Z., Yuan, C., Long, X., Zhang, Y., Du, L.From breakup of Nuna to assembly of Rodinia: a link between the Chinese central Tianshen block and Fennoscandia.Tectonics, Doi.org/10.1029/ 2018TC005471China, Europe, Fennoscandiageochronology

Abstract: The transition from breakup of Nuna (or Columbia, 2.0-1.6 Ga) to assembly of Rodinia (1.0-0.9 Ga) is investigated by means of U?Pb and Lu?Hf data of detrital zircons from three Neoproterozoic metasedimentary rocks in the Central Tianshan Block (CTB), NW China. These data yield six age peaks around 1.0, 1.13, 1.34, 1.4-1.6, 1.75, and 2.6 Ga. Few zircons are detected between 2.0 and 2.5 Ga. The Paleoproterozoic to Neoproterozoic detrital zircons have Hf isotopic compositions (?22.1 to +13.0) similar to those of coeval magmatic rocks in the CTB, indicating a proximal provenance. These results, together with the geological evidence and the presence of 1.4 Ga orogenic granitoids in the CTB, rule out most cratons as the CTB sources but support a Fennoscandia ancestry. Zircon U?Pb ages and Hf isotopic compositions from the CTB and Fennoscandia suggest that from 1.8 to 1.4 Ga, the ?Hf(t) values increased toward more positive values, consistent with an exterior orogen characteristic that the lower crust was replaced by a juvenile arc crust. In contrast, from 1.4 to 0.9 Ga, zircon ?Hf(t) values decreased to more negative values, reflecting an interior orogen, characterized by enhanced contribution of recycled crustal material from collided continental fragments. This marked shift most likely reflected a transition from breakup of Nuna to assembly of Rodinia, accomplished by a transformation from an exterior orogen to an interior one.
DS202002-0193
2020
Hurt, S.M., Wolf, A.S.Anomalous structure of MgCO3 liquid and the buoyancy of carbonatite melts.Earth and Planetary Science Letters, Vol. 531, 10p. PdfMantlecarbonatite

Abstract: MgCO3 is one of the most important components of mantle-derived carbonatite melts, and yet also one of the most difficult to study experimentally. Attempts to constrain its thermodynamic properties are hampered by decarbonation, which occurs at only ?500 °C, far below its metastable 1 bar melting temperature. Molecular dynamic simulations, however, can predict the thermodynamic properties of the MgCO3 liquid component in spite of experimental challenges. Using the recently developed empirical potential model for high-pressure alkaline-earth carbonate liquids (Hurt and Wolf, 2018), we simulate melts in the MgCO3-CaCO3-SrCO3-BaCO3 system from 773 to 2373 K up to 20 GPa. At 1 bar, MgCO3 liquid assumes a novel topology characterized by a 4-fold coordination of the metal cation (Mg) with both the carbonate molecule and oxygen ion; this is distinct from the other alkaline-earth carbonate liquids in which the metal cation is in ?6- and ?8-fold coordination with carbonate and oxygen. With increasing pressure, MgCO3 liquid structure becomes progressively more like that of (Ca, Sr, Ba)CO3 liquids with approaching 6-fold coordination with carbonate groups. The novel network topology of MgCO3 liquid results in a melt that is significantly more buoyant and compressible than other alkaline-earth carbonate liquids. Simulations of mixed MgCO3-bearing melts show that metal cation coordination with O and C is independent of bulk composition. Mixed simulation also reveal that molar volume, compressibility, enthalpy and heat capacity do not mix ideally with (Ca, Sr, Ba)CO3 liquids at 1 bar, a consequence of preferential metal-cation ordering in MgCO3-bearing mixtures. As pressure increases, however, mixing progressively approaches ideality with respect to molar volume, becoming nearly ideal by 12 GPa. The model is further applied to mantle-derived primary carbonatite melts with compositions, temperatures and pressures determined by published phase equilibrium experiments. The voluminous structure of liquid MgCO3 results in a buoyant melt that inhibits a density crossover with the surrounding mantle. Assuming FeCO3 liquid also adopts the same anomalous high-volume structure as MgCO3, we predict that even the most Fe-rich ferrocarbonatites would remain buoyant and be barred from sinking or stagnating in the mantle.
DS202005-0738
2020
Hutchison, M.T.Data methods applied to Greenland diamond exploration package.Ministry of Mineral Resources Report, Government of Greenland, 6,895KB pdfEurope, GreenlandData

Abstract: The Government of Greenland’s Diamond exploration data package compiles over 50 years of diamond exploration data. In addition to samples derived from Greenland’s established areas of diamondiferous rocks in central West Greenland, a wide coverage of regional exploration data extending throughout the country is included. The database follows a similar methodology of attribution and has a compatible structure to the Diamond exploration databases of the Northern Territory of Australia and Western Australia, and so meets international standards applied in areas of diamond mining. The Diamond exploration data package is the first of its kind to collate diamond exploration data country-wide in a publicly accessible fashion. It incorporates the locations of 25 000 diamond exploration samples. Associated with these samples are over 109 000 good-quality chemical analyses of mineral separate grains integrated into a standardised framework. In total, 100 discrete, named in-situ bodies, which in principle have diamond potential (kimberlites, lamproites, ultramafic lamprophyres, and carbonatites) have also been compiled in the diamond exploration data package. These occur among over 3 000 compiled in situ occurrences of dykes, pipes, sills and blows. With considerable data generated from bulk sampling of diamondiferous bodies, notably Garnet Lake, Qeqertaa and Majuagaa, this part of the database considerably expands upon previous compilations of relevant Greenland rocks, including the Geological Survey of Denmark and Greenland’s Report 2004-117. As a companion, 56 emplacement age determinations from 36 bodies are reported, encompassing most of the geographic extent of Greenland’s known rocks with diamond potential. Analyses of the exploration data allow for an understanding of exploration history in areas of known occurrences and identification of considerable gaps in the exploration coverage within areas of diamond potential. The Diamond exploration data package stands as a means to support and encourage future diamond exploration in Greenland in addition to further establishing a rigorous framework suitable for development of diamond exploration databases elsewhere.
DS202005-0739
2020
Hutchison, M.T.Greenland diamond exploration data package.www.trigon-gs.com/ publications_ms.html, external link free downloadEurope, GreenlandData

Abstract: The Department of Geology within the Mineral Resources Authority is pleased to announce the publication and release of a Greenland diamond exploration package. Greenland has seen significant diamond exploration, but remains heavily underexplored. The last diamond data package for Greenland was produced in 2004. However, considerable exploration has since been undertaken, generating abundant new exploration data. The new data package, covering the whole of Greenland, doubles the size of the previously available data. Furthermore, new discoveries of world-class significance were made in Greenland over the last fifteen years, which feature in the new product. The new diamond exploration data package collates publicly available, up-to-date information on Greenland’s diamond exploration history and sampling data from all across Greenland. It focuses on the locations of diamond-relevant rocks in-situ and as float, and the physical sampling and results of geochemical testing of these rocks. The package includes over 24,000 sample locations with over 10,000 being positive for diamond indicators. Accompanying these sample locations, there are over 121,000 mineral chemical analyses and detailed descriptions of over 1,000 diamonds. The database furthermore includes 3,000 in-situ locations of kimberlite, ultramafic lamprophyre, carbonatite and lamproites, in some cases with outcrop polygons and polylines, and geochronology data. Geophysical and remote sensing data are included by reference to other sources. Data are presented in raw formats and spatially as ArcMap and QGIS projects and as MapInfo files, as well as sample and analytical databases, and diamond-relevant exploration and survey reports. The package was commissioned by the Department of Geology, Mineral Resources Authority, and created by Mark T. Hutchison, Trigon GeoServices. To access the data package, contact us at [email protected], and you will receive the package through an ftp folder. The free data package aligns with the Mineral Resources Authority’s policy of publishing free, high quality, exploration-relevant geoscientific data. The data package highlights that Greenland has a major diamond potential. With this diamond data package, the Mineral Resources Authority aims to spark interest and support exploration for diamonds in Greenland.
DS202009-1631
2020
Hyung, E., Jacobsen, S.The 142Nd/144 Nd variations in mantle derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present.Proceedings of the National Academy of Sciences, Voll. 176, no. 26, 14738-44. pdfMantleplate tectonics

Abstract: Early silicate differentiation events for the terrestrial planets can be traced with the short-lived 146Sm-142Nd system (?100-My half-life). Resulting early Earth-produced 142Nd/144Nd variations are an excellent tracer of the rate of mantle mixing and thus a potential tracer of plate tectonics through time. Evidence for early silicate differentiation in the Hadean (4.6 to 4.0 Ga) has been provided by 142Nd/144Nd measurements of rocks that show both higher and lower (±20 ppm) values than the present-day mantle, demonstrating major silicate Earth differentiation within the first 100 My of solar system formation. We have obtained an external 2? uncertainty at 1.7 ppm for 142Nd/144Nd measurements to constrain its homogeneity/heterogeneity in the mantle for the last 2 Ga. We report that most modern-day mid-ocean ridge basalt and ocean island basalt samples as well as continental crustal rocks going back to 2 Ga are within 1.7 ppm of the average Earth 142Nd/144Nd value. Considering mafic and ultramafic compositions, we use a mantle-mixing model to show that this trend is consistent with a mantle stirring time of about 400 My since the early Hadean. Such a fast mantle stirring rate supports the notion that Earth’s thermal and chemical evolution is likely to have been largely regulated by plate tectonics for most of its history. Some young rocks have 142Nd/144Nd signatures marginally resolved (?3 ppm), suggesting that the entire mantle is not equally well homogenized and that some silicate mantle signatures from an early differentiated mantle (>4.1 Ga ago) are preserved in the modern mantle.
DS202007-1149
2019
In Color MagazineThe Russian emerald saga - The Mariinsky Priisk mine.incolorMagazine.com, Vol. Fall pp. 26-46.Russiadeposit - Mariinsky Priisk
DS202001-0020
2020
Ionov, D.A., Guo, P., Nelson, W.R., Shirey, S.B., Willbold, M.Paleoproterozoic melt depleted lithospheric mantle in the Khanka block, far eastern Russia: inferences for mobile belts bordering the North China and Siberian cratons.Geochimica et Cosmochimica Acta, Vol. 270, pp. 95-111.China, Russiametasomatism, melting

Abstract: The eastern part of Asia between the North China and Siberian cratons contains orogenic belts formed by the Paleo-Asian and Pacific subduction and older continental blocks. A fundamental question regarding these and all mobile belts is the fate of the continental lithospheric mantle (CLM) during their formation, i.e. whether, or to what extent the CLM may be formed, replaced or affected during orogeny. Insights into these processes can be obtained from mantle xenoliths hosted by Cenozoic basalts in the Proterozoic Khanka block in the far eastern Russia between NE China and the Pacific coast of Asia. We report petrographic, chemical, and Os-Sr-Nd isotope data for spinel peridotite xenoliths at two Khanka sites: Sviyagin and Podgelban. The modal abundances and chemical compositions suggest that the peridotites are residues of low to moderate degrees of melt extraction from fertile mantle. They show an 187Os/188Os vs. 187Re/188Os correlation with an apparent 1.9?Ga age; the 187Os/188Os ratios are positively correlated with Al2O3 and other melt extraction indices. These results provide the first robust CLM age constraints for the eastern Central Asian Orogenic Belt (CAOB). The ages suggest that the ancient CLM of the Khanka block may be roughly coeval with reworked CLM at Hannuoba (North China craton), and that it persisted through the Phanerozoic orogenies. Moreover, despite the proximity to Phanerozoic subduction zones, the Khanka CLM shows little post-melting enrichment, e.g. the clinopyroxenes are typically LREE-depleted and have Sr-Nd isotope ratios typical of the MORB mantle. We posit that the metasomatism of the CLM, earlier proposed for North China xenolith suites and ascribed to the effects of Pacific or older subduction and related mantle upwelling, may not be widespread in the CAOB. In general, Proterozoic blocks composed of residual peridotites may be more common in the CLM of the SE Siberia and northern China, and possibly other orogenic belts, than previously thought.
DS202002-0194
2020
Ionov, D.A., Guo, P., Nelson, W.R., Shirey, S.B., Willbold, M.Paleoproterozoic melt depleted lithospheric mantle in the Khanka block, far eastern Russia: inferences for mobile belts bordering the North China and Siberian cratons.Geochimica et Cosmochimica Acta, Vol. 270, pp. 95-111.Russiaperidotites

Abstract: The eastern part of Asia between the North China and Siberian cratons contains orogenic belts formed by the Paleo-Asian and Pacific subduction and older continental blocks. A fundamental question regarding these and all mobile belts is the fate of the continental lithospheric mantle (CLM) during their formation, i.e. whether, or to what extent the CLM may be formed, replaced or affected during orogeny. Insights into these processes can be obtained from mantle xenoliths hosted by Cenozoic basalts in the Proterozoic Khanka block in the far eastern Russia between NE China and the Pacific coast of Asia. We report petrographic, chemical, and Os-Sr-Nd isotope data for spinel peridotite xenoliths at two Khanka sites: Sviyagin and Podgelban. The modal abundances and chemical compositions suggest that the peridotites are residues of low to moderate degrees of melt extraction from fertile mantle. They show an 187Os/188Os vs. 187Re/188Os correlation with an apparent 1.9?Ga age; the 187Os/188Os ratios are positively correlated with Al2O3 and other melt extraction indices. These results provide the first robust CLM age constraints for the eastern Central Asian Orogenic Belt (CAOB). The ages suggest that the ancient CLM of the Khanka block may be roughly coeval with reworked CLM at Hannuoba (North China craton), and that it persisted through the Phanerozoic orogenies. Moreover, despite the proximity to Phanerozoic subduction zones, the Khanka CLM shows little post-melting enrichment, e.g. the clinopyroxenes are typically LREE-depleted and have Sr-Nd isotope ratios typical of the MORB mantle. We posit that the metasomatism of the CLM, earlier proposed for North China xenolith suites and ascribed to the effects of Pacific or older subduction and related mantle upwelling, may not be widespread in the CAOB. In general, Proterozoic blocks composed of residual peridotites may be more common in the CLM of the SE Siberia and northern China, and possibly other orogenic belts, than previously thought.
DS202007-1150
2020
Ionov, D.A., Liu, Z., Li, J., Golovin, A.V., Korsakov, A.V., Xu, Y.The age and origin of cratonic lithospheric mantle: Archean dunites vs paleoproterozoic harzburgites from the Udachnaya kimberlite, Siberian craton.Geochimica et Cosmochimica Acta, Vol. 281, pp. 67-90. pdfRussia, Siberiadeposit - Udachnaya

Abstract: Cratonic lithospheric mantle is believed to have been formed in the Archean, but kimberlite-hosted coarse peridotites from Udachnaya in the central Siberian craton typically yield Paleoproterozoic Re-depletion Os isotope ages (TRD). By comparison, olivine megacrysts from Udachnaya, sometimes called “megacrystalline peridotites”, often yield Archean TRD ages, but the nature of these rare materials remains enigmatic. We provide whole-rock (WR) Re-Os isotope and PGE analyses for 24 olivine-rich xenoliths from Udachnaya as well as modal and petrographic data, WR and mineral major and trace element compositions. The samples were selected based on (a) high olivine abundances in hand specimens and (b) sufficient freshness and size to yield representative WR powders. They comprise medium- to coarse-grained (olivine??1?cm) dunite, olivine megacrysts and low-orthopyroxene (11-21% opx) harzburgites equilibrated at 783-1154?°C and 3.9-6.5 GPa; coarse dunites have not been previously reported from Udachnaya; two xenoliths contain ilmenite. The harzburgites and dunites have similar WR variation ranges of Ca, Al, Fe, Cr and Mg# (0.917-0.934) typical of refractory cratonic peridotites, but the dunites tend to have higher MgO, NiO and Mg/Si. Mineral abundances and those of Ca and Al are not correlated with Mg#WR; they are not due to differences in melting degrees but are linked to metasomatism. Several samples with high 187Re/188Os show a positive linear correlation with 187Os/188Os with an apparent age of 0.37?Ga, same as eruption age of host kimberlite. Robust TRD ages were obtained for 16 xenoliths with low 187Re/188Os (0.02-0.13). TRD ages for low-opx harzburgites (1.9-2.1?Ga; average 2.0?±?0.1?Ga, 1 ?) are manifestly lower than for dunites and megacrysts (2.4-3.1?Ga); the latter define two subsets with average TRD of 2.6?±?0.1?Ga and 3.0?±?0.1?Ga, and TMA of 3.0?±?0.2?Ga and 3.3?±?0.1?Ga, respectively. Differences in olivine grain size (coarse vs. megacrystalline) are not related to age. The age relations suggest that the dunites and megacrysts could not be produced by re-melting of harzburgites, e.g. in arc settings, nor be melt channel materials in harzburgites. Instead, they are relict fragments of lithospheric mantle formed in the Archean (likely in two events at or after 2.6?Ga and 3.0?Ga) that were incorporated into cratonic lithosphere during the final assembly of the Siberian craton in the Paleoproterozoic. A multi-stage formation of the Siberian lithospheric mantle is consistent with crustal basement ages from U-Pb dating of zircons from crustal xenoliths at Udachnaya and detrital zircons from the northern Siberian craton (1.8-2.0, 2.4-2.8 and 3.0-3.4?Ga). The new data from the Siberian and other cratons suggest that the formation of strongly melt-depleted cratonic lithosphere (e.g. Mg# ?0.92) did not stop at the Archean-Proterozoic boundary as is commonly thought, but continued in the Paleoproterozoic. The same may be valid for the transition from the ‘Archean’ (4-2.5?Ga) to modern tectonic regimes.
DS202009-1632
2020
Iskrina, A., Spivak, A.V., Bobrov, A.V., Eremin, N.N., Marchenko, E.I., Dubrovinsky, L.S.Synthesis and crystal structures of new high-pressure phases CaAl2O4 and Ca2Al6O11.Lithos, Vol. 374-375, 6p. PdfMantlegarnet

Abstract: The phases of CaAl2O4 and Ca2Al6O11 were synthesized at 15 GPa and 1600 °C. Microprobe data gave formulae Ca1.003Al1.998O4 and Ca2.05Al5.97O11, on the basis of 4 and 11 oxygen atoms. The crystal structures have been refined by single-crystal X-ray diffraction. Orthorhombic unitcell parameters for CaAl2O4 are a = 8.8569(10) Å; b = 2.8561(4) Å; c = 10.2521(11) Å; V = 259.34(5) Å3; Z = 8 (space group Pnma). The Ca2Al6O11 phase was obtained for the first time. It crystallizes with a space group P42/mnm and has lattice parameters a = b = 11.1675(4) Å; c = 2.83180(10) Å; V = 353.16(2) Å3; Z = 2. A Raman spectrum was obtained for a new phase for the first time. Our results suggest that both studied phases are stable under the condition of the transition zone and can be considered as potential aluminum concentrators in the Earth's deep geospheres.
DS202011-2045
2007
Ivanic, T.The chrome-garnet peridotite assemblages and their role in the evolution of the mantle lithosphere.Phd Thesis, University of Edinbugh, 257p. Pdf Africa, South Africadeposit - Newlands, Bobbejaan

Abstract: Newlands and Bobbejaan kimberlites, South Africa, contain suites of highly chromian, garnet-rich peridotites amongst their xenolith population and an investigation of these xenoliths has been targeted because there is an overlap of mineral compositions withthe garnet-chromite-olivine paragenesis found as inclusions in diamonds. A high proportion of garnets and chromites in these rocks plot in the diamond facies fields on Cr2O3-CaO and Cr2O3-MgO wt. % plots respectively. However, it has also been found that many Cr-rich assemblages are clinopyroxene-bearing (lherzolitic) as well as harzburgitic (i.e. forming arange of chromite-garnet peridotite assemblages). Many samples have garnets with inclusions of serpentine ± chromite (+ clinopyroxene in lherzolitic samples) whose arrangement are sometimes indicative of exsolution or annealed exsolution textures. Initial bulk REE patterns were calculated for the pre-exsolution, pre-metasomatism, high-Cr garnets. The patterns found are humped for harzburgitic samples and relatively flat for lherzolitic ones. These appear to be closely linked to the concentration of Ca in garnet indicative of a single-stage formation process for the humped profiles. The profiles were later modified by exsolution of pyroxenes (with a clear link between Ca content of garnet and the garnet/clinopyroxene partition coefficients) and, in a few cases, by metasomatism causing a zonation of REE.Most of the garnets have strongly developed zonation patterns which are a result of diffusion towards the matrix (external zonation) followed by zonation towards inclusions (internal zonation). Cr-Al and Mg-Ca inter-diffuse in both types of zonation; Ti may also be strongly zoned, whereas Fe is not distinctly zoned in any sample. External zonation may be divided into ‘P-T re-equilibration’ and ‘metasomatic’ types, where the former type conforms to down-P-T garnet-spinel transition reaction simulations and the latter does not. All internal zonations conform to down P-T reaction simulations. All the zonation profiles conform well to diffusion controlled reaction models. External P-T re-equilibration is modelled to have occurred on an order of magnitude greater timescale than internal zonation (~5 Ma compared to ~0.5 Ma using DMg= 10-20m2 /s). Metasomatic zonation occurs over the longest diffusion distances and is modelled to have timescales up to 20 Ma. Based upon the geometries of chemical heterogeneity in the minerals analysed, a sequence of events has been proposed for the evolution of the Newlands and Bobbejaan samples: (1) Earliest known mineralogy. Thereis little evidence for the events prior to and during this stage. However, the modal mineralogy is postulated to have been more garnet and olivine-rich than seen in the samples and the crystals more chemically homogeneous. The P and T in samples are modelled to have the highest Ps and Ts of all stages (potentially > 65kb and > 1350°C). (2) Exsolution.This stage represents the initiation of an event which significantly lowered P and T where spinel and pyroxene exsolved from garnet. (3a) External zonation - P-T re-equilibration and metasomatism. These events are contiguous with stage 2 and P-T estimates for this stage indicate further lowering of P and T. This is accompanied by modification of a few samples by the infiltration of metasomatic fluid. (3b) Internal zonation – P-T re-equilibration. This stage represents the final lowering of P and T, yielding final P-T estimates on clinopyroxene inclusion-garnet boundaries of 38-50 kb and 900-1150°C. These P-T estimates place samples plot on a relatively cool continental steady state geotherm. (4) Kimberlite eruption. The initial formation of the garnet-rich rock types with their (calculated) highly chromian composition and particular initial REE compositions appears to be related to a major depletion event with subsequent burial. Differential interaction with a CO2-bearing fluid would generate the range of harzburgitic and lherzolitic compositions found. However it is acknowledged that this is difficult to determine and constrain because of the lack of preservation of evidence prior to Stage 2.The down-P-T event has a similar timescale and associated uplift rate to be related to continent-continent collision according to the time scales for diffusion. The contemporaneous metasomatism leads to postulation that the event may have been related to the continental accretion of the eastern and western parts of the Kaapvaal craton in the late Archaean. In terms of the relation to diamond, it was found that samples with high-Cr harzburgitic garnets tended to yield P-T estimates that were most substantially into the diamond stability field based upon the Cr-Al partitioning between garnet and spinel and also modelling the samples using the computer programme known as‘Perplex’. Clinopyroxene-bearing samples (i.e. those with a bulk rock composition higher inCa) tended to indicate higher temperatures of equilibration. Cr-spinels from the harzburgitic paragenesis have higher Mg and lower Ti than the lherzolitic Cr-spinels, but overlapping Cr compositions at high Cr and may be differentiated on Cr-Mg and Cr-Ti compositional plots.
DS202012-2221
2021
Jackson, C.R.M., Cottrell, E., Andrews, B.Warm and oxidizing slabs limit ingassing efficiency of nitrogen to the mantle.Earth and Planetary Letters, Vol. 553, 116515, 12p. PdfMantlenitrogen

Abstract: Nitrogen is a major and essential component of Earth's atmosphere, yet relative to other volatile elements, there are relatively few experimental constraints on the pathways by which nitrogen cycles between Earth's interior and exterior. We report mineral-melt and mineral-fluid partitioning experiments to constrain the behavior of nitrogen during slab dehydration and sediment melting processes. Experiments reacted rhyolitic melts with silicate and oxide minerals, in the presence of excess aqueous fluid, over temperatures between 725-925 °C and pressures between 0.2 and 2.3 GPa. Oxygen fugacity ranged between iron metal saturation (?NNO-5) to that in excess of primitive arc basalts (?NNO+2). Our experiments demonstrate that hydrous fluid is the preferred phase for nitrogen over minerals (biotite, K-feldspar, and amphibole) and rhyolitic melts across all conditions explored. Relatively large effects of pressure (?log()/?(GPa/K) = 761 ± 68 (1?), ?log()/?(GPa/K) = 462 ± 169) and moderate effects of oxygen fugacity (NNO = -0.20 ± 0.04, ?logNNO = -0.10 ± 0.04) modulate partitioning of nitrogen. We further document negligible partitioning effects related to mineral composition or Cl content of hydrous fluid. Of the minerals investigated, biotite has the largest affinity for N and should control the retention of N in slabs where present. Application of partitioning data to slab dehydration PT paths highlights the potential for highly incompatible behavior ( < 0.1) from the slab along warmer and oxidized (NNO+1) subduction geotherms, whereas dehydration along reduced and cooler geotherms will extract moderate amounts of nitrogen ( > 0.1). We find that slab melting is less effective at extracting N from slabs than fluid loss, at least under oxidized conditions (NNO+1). Ultimately, the conditions under which slabs lose fluid strongly affect the distribution of nitrogen between Earth's interior and exterior.
DS202001-0021
2019
Jacques, J.F.An eye on diamonds. The way diamonds are utilised for ophthalmic surgery.Gems & Jewellery, Vol. 28, 4, pp. 22-23.GlobalCryo-EM
DS202008-1402
2020
Jalowitzki, T., Gervasoni, F., Sumino, H., Klemme, S., Berndt, J., Dalla Costa, M., Fuck, R.A.Plume subduction events recorded by KS2 kimberlite indicator minerals from Juina, Brazil.Goldschmidt 2020, 1p. AbstractSouth America, Brazil, Mato Grossodeposit - Juina

Abstract: The Cretaceous Juína Kimberlite Province (JKP, 95-92 Ma) is located in the southwest of the Amazonian Craton, northwest of Mato Grosso, Brazil. Here we present new geochemical and isotopic data of garnet (n=187) and zircon (n=25) megacrysts collected from the KS2 kimberlite. The magmatic zircon megacrysts have U-Pb ages of 92.1 ± 0.7 Ma. The chondrite-normalized rare earth element (REE) patterns (LREE
DS202009-1633
2020
Jaques, A.L., Brink, F., Chen, J.Magmatic haggertyite in olivine lamproites of the West Kimberley region, western Australia.The American Mineralogist, in press available, 31p. PdfAustralialamproites
DS202012-2222
2020
Jaques, A.L., Brink, F., Chen, J.Magmatic haggertyite in olivine lamproites of the West Kimberley region, Western Australia.American Mineralogist, Vol. 105, pp. 1724-1733.Australialamproites

Abstract: We report the first occurrence of magmatic haggertyite (BaFe6Ti5MgO19) from the Miocene lamproites of the West Kimberley region of Western Australia. This contrasts with the metasomatic formation reported in an olivine lamproite host at the type locality, Prairie Creek, Arkansas. Haggertyite occurs in the groundmass of a diamondiferous olivine lamproite pipe in the Ellendale field, and within the large zoned Walgidee Hills lamproite where it forms part of an extensive suite of Ba- and K-bearing titanate and Ti-rich silicate minerals. The haggertyite co-exists with chromian spinel, perovskite, and ilmenite in the Ellendale lamproite, and with priderite and perovskite and, in one locality, with priderite, jeppeite, ilmenite, and perovskite, in the Walgidee Hills lamproite. Unlike priderite and perovskite, which are common groundmass phases in the Ellendale olivine lamproites and present throughout the Walgidee Hills lamproite, haggertyite appears restricted in its occurrence and crystallization interval, with sparse ilmenite apparently mostly crystallizing as an alternative phase. In the Walgidee Hills lamproite the haggertyite-bearing assemblage is succeeded by the Ba-titanate assemblage priderite plus jeppeite in the evolved central part of the body. The haggertyite in the main zone of the Walgidee Hills lamproite has an average composition of (Ba0.7K0.3)1.0(Ti5.0Fe3+2.1Cr0.1Fe2+3.8Mn0.2Mg0.6Na0.1)12O19 and is thus very similar to the original haggertyite described from xenoliths in the Prairie Creek lamproite apart from being poorer in Cr and Ni. Haggertyite in the groundmass of the Ellendale olivine lamproite and the central zone of the Walgidee Hills lamproite, in addition to variations in Mg and Cr, show significant variation in Ti and Fe contents and in calculated Fe3+ and Fe2+. A linear inverse relationship between Ti and Fe, and Ti and Fe3+, indicates that Fe3+ is accommodated by the coupled substitution Ti4+ + Fe2+ ? 2 Fe3+. A marked trend to higher Fe3+ in the haggertyite in Ellendale 9 olivine lamproite is ascribed to increasing oxidation during crystallization, with fO2 estimated from the olivine-spinel thermometer and oxygen barometer at Dlog FMQ = -1 to +3 at temperatures of 790-660 °C. The haggertyite in the central zone of the Walgidee Hills lamproite, in contrast, shows a marked trend to Fe2+ enrichment, which is associated with decreasing Fe in perovskite. This is inferred to indicate formation under more reducing conditions, but sufficiently oxidized to permit Fe3+ in co-existing priderite and jeppeite. Trace-element analysis by LA-ICP-MS shows the Walgidee Hills haggertyite contains minor amounts of Na, Si, Ca, V, Co, Zn, Sr, Zr, Nb, and Pb, and only traces of Al, P, Sc, Rb, REE, Hf, and Ta. Moreover, the haggertyite is preferentially enriched in certain lithophile (Ba, Sr), siderophile (Mn, Fe, Co, Ni), and chalcophile (Zn, Pb) elements relative to co-existing priderite. Haggertyite crystallization appears to be a consequence not only of the very high Ba, Ti, and K contents of the lamproite, but of relatively high-Fe concentrations and low temperatures in evolved olivine lamproite magma with the Fe3+/Fe2+ ratio determined by the prevailing fO2. The new data suggest that haggertyite might also be present but previously unrecognized in the evolved groundmass of other olivine lamproites. Haggertyite is one of an increasing number of new minerals in upper mantle rocks and volcanics derived from the upper mantle hosting large-ion-lithophile and high field strength cations.
DS202008-1403
2020
Jeffay, J.Size still matters. History of Cullinan diamond.Idexonline Memo , July 2, 2p.Africa, South Africadeposit - Premier
DS202008-1404
2020
Jeffay, J.Daytrip Mom finds 2.23 carat brown diamond at "Dig your own" mine.Idexonline Memo , June 30, 1p.United States, Arkansasdeposit - Crater of Diamonds
DS202003-0343
2020
Jellinek, M., Lenardic, A., Pierrehumbert, R.T.Ice, fire, or fizzle: the climate footprint of Earth's supercontinental cycles.Geochemistry, Geophysics, Geosystems, Vol. 21, 2, 66p. PdfMantlegeodynamics

Abstract: Supercontinent assembly and breakup can influence the rate and global extent to which insulated and relatively warm subcontinental mantle is mixed globally, potentially introducing lateral oceanic?continental mantle temperature variations that regulate volcanic and weathering controls on Earth's long?term carbon cycle for a few hundred million years. We propose that the relatively warm and unchanging climate of the Nuna supercontinental epoch (1.81.3 Ga) is characteristic of thorough mantle thermal mixing. By contrast, the extreme cooling?warming climate variability of the Neoproterozoic Rodinia episode (10.63 Ga) and the more modest but similar climate change during the Mesozoic Pangea cycle (0.30.05 Ga) are characteristic features of the effects of subcontinental mantle thermal isolation with differing longevity. A tectonically modulated carbon cycle model coupled to a one?dimensional energy balance climate model predicts the qualitative form of Mesozoic climate evolution expressed in tropical sea?surface temperature and ice sheet proxy data. Applied to the Neoproterozoic, this supercontinental control can drive Earth into, as well as out of, a continuous or intermittently panglacial climate, consistent with aspects of proxy data for the Cryogenian?Ediacaran period. The timing and magnitude of this cooling?warming climate variability depends, however, on the detailed character of mantle thermal mixing, which is incompletely constrained. We show also that the predominant modes of chemical weathering and a tectonically paced abiotic methane production at mid?ocean ridges can modulate the intensity of this climate change. For the Nuna epoch, the model predicts a relatively warm and ice?free climate related to mantle dynamics potentially consistent with the intense anorogenic magmatism of this period.
DS202004-0520
2020
Johnson, B.W., Wing, B.A.Limited Archean continental emergence reflected in an early Archean 180-enriched ocean.Nature Geoscience, 10.1038/s41561-020-0538-9Australiawater

Abstract: The origin and evolution of Earth’s biosphere were shaped by the physical and chemical histories of the oceans. Marine chemical sediments and altered oceanic crust preserve a geochemical record of these histories. Marine chemical sediments, for example, exhibit an increase in their 18O/16O ratio through time. The implications of this signal are ambiguous but are typically cast in terms of two endmember (but not mutually exclusive) scenarios. The oceans may have been much warmer in the deep past if they had an oxygen isotope composition similar to that of today. Alternatively, the nature of fluid-rock interactions (including the weathering processes associated with continental emergence) may have been different in the past, leading to an evolving oceanic oxygen isotope composition. Here we examine approximately 3.24-billion-year-old hydrothermally altered oceanic crust from the Panorama district in the Pilbara Craton of Western Australia as an alternative oxygen isotope archive to marine chemical sediments. We find that, at that time, seawater at Panorama had an oxygen isotope composition enriched in 18O relative to the modern ocean with a ?18O of 3.3?±?0.1‰ VSMOW. We suggest that seawater ?18O may have decreased through time, in contrast to the large increases seen in marine chemical sediments. To explain this possibility, we construct an oxygen isotope exchange model of the geologic water cycle, which suggests that the initiation of continental weathering in the late Archaean, between 3 and 2.5 billion years ago, would have drawn down an 18O-enriched early Archaean ocean to ?18O values similar to those of modern seawater. We conclude that Earth’s water cycle may have gone through two separate phases of steady-state behaviour, before and after the emergence of the continents.
DS202012-2223
2020
Jones, D.C., Kumar, S., Lanigan, P.M.P., McGuiness, C.D., Dale, M.W., Twichen, D.J., Fisher, D., Martineau, P.M., Neil, M.A., Dunsby, C., French, P.M.W.Multidemensional luminescence microscope for imaging defect colour centres in diamond.Methods and Applications in Flouresence, Vol. 8, 1, 01404 htpp:dx.doi.org/10.1088/2050-6120/ab4eacGloballuminescence

Abstract: We report a multidimensional luminescence microscope providing hyperspectral imaging and time-resolved (luminescence lifetime) imaging for the study of luminescent diamond defects. The instrument includes crossed-polariser white light transmission microscopy to reveal any birefringence that would indicate strain in the diamond lattice. We demonstrate the application of this new instrument to detect defects in natural and synthetic diamonds including N3, nitrogen and silicon vacancies. Hyperspectral imaging provides contrast that is not apparent in conventional intensity images and the luminescence lifetime provides further contrast.
DS202006-0924
2020
Jones, T.D., Maguire, R.R., van Keken, P.E., Ritsema, J., Koelemeijer, P.Subducted oceanic crust as the origin of seismically slow lower-mantle structures.Progress in Earth and Planetary Science , Vol. 7, 16p. PdfMantlegeophysics - seismics

Abstract: Mantle tomography reveals the existence of two large low-shear-velocity provinces (LLSVPs) at the base of the mantle. We examine here the hypothesis that they are piles of oceanic crust that have steadily accumulated and warmed over billions of years. We use existing global geodynamic models in which dense oceanic crust forms at divergent plate boundaries and subducts at convergent ones. The model suite covers the predicted density range for oceanic crust over lower mantle conditions. To meaningfully compare our geodynamic models to tomographic structures, we convert them into models of seismic wavespeed and explicitly account for the limited resolving power of tomography. Our results demonstrate that long-term recycling of dense oceanic crust naturally leads to the formation of thermochemical piles with seismic characteristics similar to the LLSVPs. The extent to which oceanic crust contributes to the LLSVPs depends upon its density in the lower mantle for which accurate data is lacking. We find that the LLSVPs are not composed solely of oceanic crust. Rather, they are basalt rich at their base (bottom 100-200 km) and grade into peridotite toward their sides and top with the strength of their seismic signature arising from the dominant role of temperature. We conclude that recycling of oceanic crust, if sufficiently dense, has a strong influence on the thermal and chemical evolution of Earth’s mantle.
DS202001-0022
2019
Jones, T.J., Reynolds, C.D., Boothroyd, S.C.Fluid dynamic induced break-up during volcanic eruptions. ( mentions kimberlite and carbonatite)Nature Communications, doi.org/10.1038/ s41467-019-11750-4 7p. pdf Mantlemelting

Abstract: Determining whether magma fragments during eruption remains a seminal challenge in volcanology. There is a robust paradigm for fragmentation of high viscosity, silicic magmas, however little is known about the fragmentation behaviour of lower viscosity systems—the most abundant form of volcanism on Earth and on other planetary bodies and satellites. Here we provide a quantitative model, based on experiments, for the non-brittle, fluid dynamic induced fragmentation of low viscosity melts. We define the conditions under which extensional thinning or liquid break-up can be expected. We show that break-up, both in our experiments and natural eruptions, occurs by both viscous and capillary instabilities operating on contrasting timescales. These timescales are used to produce a universal break-up criterion valid for low viscosity melts such as basalt, kimberlite and carbonatite. Lastly, we relate these break-up instabilities to changes in eruptive behaviour, the associated natural hazard and ultimately the deposits formed.
DS202007-1151
2019
Jones, T.J., Reynolds, C.D., Boothroyd, S.C.Fluid dynamics induced break up during volcanic eruptions.Nature Communications, Vol. 10, 1, 10.1038/s41467-019-11750-4.Mantlegeodynamics

Abstract: Determining whether magma fragments during eruption remains a seminal challenge in volcanology. There is a robust paradigm for fragmentation of high viscosity, silicic magmas, however little is known about the fragmentation behaviour of lower viscosity systems—the most abundant form of volcanism on Earth and on other planetary bodies and satellites. Here we provide a quantitative model, based on experiments, for the non-brittle, fluid dynamic induced fragmentation of low viscosity melts. We define the conditions under which extensional thinning or liquid break-up can be expected. We show that break-up, both in our experiments and natural eruptions, occurs by both viscous and capillary instabilities operating on contrasting timescales. These timescales are used to produce a universal break-up criterion valid for low viscosity melts such as basalt, kimberlite and carbonatite. Lastly, we relate these break-up instabilities to changes in eruptive behaviour, the associated natural hazard and ultimately the deposits formed.
DS202007-1152
2020
Juarez-Perez, E., Haro, M.Perovskite cells take a step forward.Science, Vol 368, 6497, p. 1309.Globalperovskite

Abstract: Today's monocrystalline silicon solar cells have their throne on the roofs of our houses. In the past decade, however, perovskite solar cells (PSCs) show impressive advances with a high power conversion efficiency (PCE) of 25.2% (1) and low fabrication cost, which make this technology promising for further advances in decarbonization energy models (2). Yet the life cycle of PSCs needs to be increased for market integration. Poor stability is the main impediment to commercializing this technology. Thus, great effort has been focused on the causes and mechanisms of degradation, many of which can be mitigated or minimized with encapsulation. Various strategies have been proposed to increase PSCs' operational stability, which is affected by moisture, oxidation, heat, light, and other factors (3, 4). On page 1328 of this issue, Shi et al. (5) report a successful encapsulation procedure for hybrid PSCs.
DS202004-0521
2020
Jung, S., Hauff, F., Berndt, J.Generation of a potassic to ultrapotassic alkaline complex in a syn-collisional setting through flat subduction: constraints on magma sources and processes ( Otjimingwe alkaline complex, Damara orogen, Namibia).Gondwana Research, Vol. 82, pp. 267-287.Africa, Namibiametasomatism

Abstract: The ~545 Ma-old syn-collisional Otjimbingwe alkaline complex is composed of pyroxene-amphibole-biotite-bearing, mildly nepheline-normative to quartz-normative rocks ranging in composition from monzogabbro to monzonite, syenite and granite. The alkaline rocks have moderate to high SiO2 (50.5-73.0 wt%) and Na2O + K2O (5.1-11.5 wt%) and moderate to low MgO (6.6-0.2 wt%) concentrations. All samples have high large ion lithophile element (LILE: Ba up to 4600 ppm) and high-field-strength element contents (HFSE; Zr: 155-1328 ppm; Nb: 16-110 ppm; Ta: 1.4-7.1 ppm and Hf: 4-24 ppm) and have strongly fractionated LREE patterns ((La/Yb)N = 14-51). The most primitive members lack significant negative Eu anomalies. Mantle-normalized multi-element diagrams show depletion in Ba, Rb, Nb (Ta), P and Ti. The alkaline rocks have moderate radiogenic initial 87Sr/86Sr ratios (0.7061-0.7087) and unradiogenic initial ?Nd values (?3.9 to ?6.1). This isotope signature, associated with high LREE/HFSE ratios indicates that the parental melts were generated in enriched portions of the shallow lithospheric mantle, which was probably affected by previous subduction zone processes. In addition, correlations between Sr and Nd isotopes indicate that some of these variations result from combined crustal assimilation and fractional crystallization (AFC) processes. A new model of flat subduction is presented that explains most of the unsolved problems in the orogenic evolution of the Damara orogen, namely (i) the absence of early intrusive rocks with a clear subduction zone setting, (ii) the absence of high-pressure rocks such as blueschists and eclogites, (iii) the unusual distribution of igneous rocks with a clear predominance of granite and granodiorite and (iv) the need for a asthenospheric window during a classical subduction to explain the high T/moderate P granulite facies conditions in the overriding plate.
DS202007-1153
2020
Jung, S., Hauff, F., Berndt, J.Generation of a potassic to ultrapotassic alkaline complex in a syn-collisional setting through flat subduction: constraints on magma sources and processes ( Otjimingwe alkaline complex, Damara orogen, Namibia.Gondwana Research, Vol. 82, pp. 267-287. pdfAfrica, Namibiadeposit - Otjimbingwe

Abstract: The ~545 Ma-old syn-collisional Otjimbingwe alkaline complex is composed of pyroxene-amphibole-biotite-bearing, mildly nepheline-normative to quartz-normative rocks ranging in composition from monzogabbro to monzonite, syenite and granite. The alkaline rocks have moderate to high SiO2 (50.5-73.0 wt%) and Na2O + K2O (5.1-11.5 wt%) and moderate to low MgO (6.6-0.2 wt%) concentrations. All samples have high large ion lithophile element (LILE: Ba up to 4600 ppm) and high-field-strength element contents (HFSE; Zr: 155-1328 ppm; Nb: 16-110 ppm; Ta: 1.4-7.1 ppm and Hf: 4-24 ppm) and have strongly fractionated LREE patterns ((La/Yb)N = 14-51). The most primitive members lack significant negative Eu anomalies. Mantle-normalized multi-element diagrams show depletion in Ba, Rb, Nb (Ta), P and Ti. The alkaline rocks have moderate radiogenic initial 87Sr/86Sr ratios (0.7061-0.7087) and unradiogenic initial ?Nd values (?3.9 to ?6.1). This isotope signature, associated with high LREE/HFSE ratios indicates that the parental melts were generated in enriched portions of the shallow lithospheric mantle, which was probably affected by previous subduction zone processes. In addition, correlations between Sr and Nd isotopes indicate that some of these variations result from combined crustal assimilation and fractional crystallization (AFC) processes. A new model of flat subduction is presented that explains most of the unsolved problems in the orogenic evolution of the Damara orogen, namely (i) the absence of early intrusive rocks with a clear subduction zone setting, (ii) the absence of high-pressure rocks such as blueschists and eclogites, (iii) the unusual distribution of igneous rocks with a clear predominance of granite and granodiorite and (iv) the need for a asthenospheric window during a classical subduction to explain the high T/moderate P granulite facies conditions in the overriding plate. Graphical abstract
DS202005-0740
2020
Kaminsky, F.V.Basic problems concerning the composition of the Earth's lower mantle.Lithos, in press available, 8p. PdfMantlebridgmanite

Abstract: The last decade has seen the publication of a number of new and highly pertinent studies on the composition of the Earth's lower mantle, leading to a better understanding of the Deep Earth. A series of new lower-mantle minerals were found, having formed under natural conditions and received the following names: bridgmanite, jeffbenite, breyite, and ellinaite. Some other, as yet, unnamed oxides, phosphates, and fluorides were also discovered for the first time. Among the new mineral phases, of particular interest are cubic nitrogen and ice-VII. Their presence demonstrates a significant role of both nitrogen and of water in the Deep Earth. This new data allows for creation of a principal model for the composition of the Earth's lower mantle. By various evidences, it differs greatly to that of the upper mantle composition, and is heterogeneous.
DS202011-2046
2020
Kaminsky, F.V., Shilobreeva, S.N., Ber, B.Ya., Kazantsev, D.Yu.Quantification of hydrogen in natural diamond by secondary ion mass spectrometry. (SIMS)Doklady Earth Sciences, Vol. 494, 1, pp. 699-703. pdfSouth America, Brazilhydrogen

Abstract: The volumetric concentration of hydrogen in two Brazilian diamonds is determined using secondary ion mass spectrometry and implantation of hydrogen into an external standard sample (with a dose of 1 × 16 at/cm2 and energy of 120 KeV). The diamonds studied differ noticeably in their intensities of IR-active hydrogen from 0 to 1.5 cm-1 according to the analyses of their IR spectra. The results demonstrate that for both samples studied, the volumetric concentration of hydrogen does not exceed the reached detectable level of (1-2) × 1018 at/cm3 or 1.7-3.3 at. ppm; i.e., it is lower by an order of magnitude than in the early chemical analysis and by 2-3 orders of magnitude lower than the results of the ion-beam spectrochemical, nuclear-physical, and ERDA analyses. Only a part of the hydrogen forms optically active impurities in diamond crystals and can be determined by spectral methods.
DS202007-1154
2020
Kane, R.E.America's Royal Gem Montana and Yogo sapphires.incolorMagazine.com, Vol. winter pp. 30-39.United States, Montanadeposit - Yogo sapphires
DS202009-1634
2020
Kaneva, E., Shendrik, R.Yu., Radomskaya, T.A., Suvorova, L.E.Fedorite from Murun alkaline complex ( Russia): spectroscopy and crystal chemical features.Minerals ( MDPI), Vol. 10, 702, 24p. PdfRussiadeposit - Murun

Abstract: Fedorite is a rare phyllosilicate, having a crystal structure characterized by SiO4-tetrahedral double layers located between continuous layers formed by edge-sharing (Ca,Na)-octahedra, and containing interlayer K, Na atoms and H2O molecules. A mineralogical-petrographic and detailed crystal-chemical study of fedorite specimens from three districts of the Murun alkaline complex was performed. The sequence of the crystallization of minerals in association with fedorite was established. The studied fedorite samples differ in the content of interlayer potassium and water molecules. A comparative analysis based on polyhedral characteristics and deformation parameters was carried out. For the first time, EPR, optical absorption and emission spectra were obtained for fedorite. The raspberry-red coloration of the mineral specimens could be attributed to the presence of Mn4+ ions.
DS202010-1847
2020
Kaneva, E.V., Shendrik, R.Yu., Radomskaya, T.A., Suvorova, L.F.Fedorite from Murun alkaline complex ( Russia): spectroscopy and crystal chemical features.Minerals, Vol. 10, 702 10.3390/min10080702 24p. PdfRussia, Yakutiadeposit - Murun

Abstract: Fedorite is a rare phyllosilicate, having a crystal structure characterized by SiO4-tetrahedral double layers located between continuous layers formed by edge-sharing (Ca,Na)-octahedra, and containing interlayer K, Na atoms and H2O molecules. A mineralogical-petrographic and detailed crystal-chemical study of fedorite specimens from three districts of the Murun alkaline complex was performed. The sequence of the crystallization of minerals in association with fedorite was established. The studied fedorite samples differ in the content of interlayer potassium and water molecules. A comparative analysis based on polyhedral characteristics and deformation parameters was carried out. For the first time, EPR, optical absorption and emission spectra were obtained for fedorite. The raspberry-red coloration of the mineral specimens could be attributed to the presence of Mn4+ ions.
DS202008-1405
2020
Kara, J., Vaisanen, M., Heinonen, J.S., Lahaye, Y., O'Brien, H., Huhma, H.Tracing arcologites in the Paleoproteroic era - a shift from 1.88 Ga calc-alkaline to 1.86 Ga high-Nb and adakite-like magmatism in central Fennoscandian shield.Lithos, in press available, 68p. PdfEurope, Fennoscandiaalkaline
DS202008-1406
2020
Kargin, A.V., Kamenetsky, V.S.Links between ultramafic lamprophyres and kimberlites in the Anabar shield, Yakutia, Russia: evidence from multiphase inclusions in rock-forming minerals.Goldschmidt 2020, 1p. AbstractRussia, Yakutiadeposit - Viktoria

Abstract: To provide new constraints on the evolution of ultramafic lamprophyre melts and relation to kimberlites, we examined monomineralic and primary multiphase melt inclusions in rock-forming minerals within damtjernite from Viktoria pipe, Anabar region, Siberia craton, Russia. The studied samples are relatively unaltered nepheline-bearing, carbonate-poor damtjernite with a significant amount of monticellite in the groundmass and as a replacement of olivine. Studied inclusions hosted by groundmass monticellite, magnesian ulvöspinel-magnetite and perovskite. Monomineralic inclusions sized up to 10 ?m are round-toeuhedral in shape and are comprised of monticellite, spinel, perovskite and nepheline. Multiphase melt inclusions sized up to 10-15 ?m have rounded to elongate and amoeboid shapes. These inclusions are heterogeneous in composition and consist of perovskite, spinel group minerals, apatite (including F- and Sr-apatite), feldspathoids, multiphase alkali (Na, K) carbonate and chloride (sylvite/halite), rare K-Naand Ba-sulfates, phlogopite and baddeleyite. Despite the lack of carbonate phases in studied rocks, the composition of multiphase inclusions indicates that lamprophyre melts contained carbonate or carbonate/chlorite components. The CO2 degassing is consistent with the reaction between olivine and carbonate-bearing melt led to decarbonation reaction and generation of montichellite, as described in [1]. The composition of multiphase inclusions within minerals from lamprophyres is close to the composition of multiphase inclusions within olivine, spinel, monticellite, perovskite from kimberlites, thus indicating possible genetic links between parental melts of ultramafic lamprophyre and kimberlite.
DS202010-1848
2020
Kargin, A.V., Nosova, A.A., Babarina, I.I., Dokuchaev, A.Ya., Kondrashov, I.A.Paleproterozoic kimberlites of Kimozero: petrographic facies recstruction of kimberlite pipe overcoming tectonic and metamorphic modification.Doklady Earth Sciences, Vol. 493, 1, pp. 522-525.Russiadeposit - Kimozero

Abstract: Based on a detailed petrographic investigation and geological observations of the Paleoproterozoic Kimozero kimberlite (Karelia, Russia), we present a new model of kimberlite pipe with multiphase and mono-crater structure. We recognised volcanoclastic and coherent kimberlite series that filled the inner and outer zones of the kimberlite crater. The multiphase structure, emplacement style, petrography and reconstructed size of the Kimozero kimberlite correspond to Phanerozoic kimberlite pipes.
DS202008-1407
2020
Kargin, A.V., Nosova, A.A., Sazonova, L.V., Peresetskaya, E.V., Golubeva, Yu.Yu., Lebedeva, N.M., Tretyachenko, V.V., Khvostikov, V.A., Burmii, J.P.Ilmenite from the Arkangelsk diamond province, Russia: composition, origin and indicator of diamondiferous kimberlites.Petrology, Vol. 28, 4, pp. 341-369. pdfRussia, Archangelilmenite

Abstract: To provide new insights into the origin and evolution of kimberlitic magmas with different diamond concentrations from the Arkhangelsk diamond province in northwestern Russia, we examined the major-and trace-element compositions of ilmenite from diamondiferous kimberlite of the Grib pipe and diamond barren kimberlites from the Kepino cluster (Stepnaya and TsNIGRI-Arkhangelskaya pipes). Ilmenite from diamond-barren kimberlites shows lower Mg, Ti, Cr, Ni and Cu concentrations with increase in both Fe 3+ and Fe 2+ and Nb, Ta, Zr, Hf, Zn and V concentrations. The main differences between kimberlites with different diamond contents are the Nb and Zr concentrations and their correlation patterns with Mg and Cr concentrations. Ilmenite from the Grib kimberlite has Zr concentrations <110 ppm, whereas ilmenite from the Kepino kimberlites has Zr concentrations >300 ppm. Ilmenite crystallisation within the Grib kimberlite occurred under increasing oxygen fugacity (fO 2), which may reflect assimilation of mantle peridotite by the kimberlitic magmas. Ilmenite from the Kepino kimberlites suggests its crystallisation under constant fO 2 , with the ilmenite composition being controlled by processes of fractional crystallisation of megacrystic minerals. These assumptions were confirmed with assimilation-fractional crystallisation calculations. On the basis of obtained data, we developed a model for the evolution of the kimberlitic magmas for both diamon-diferous and barren kimberlites. The diamond-bearing kimberlitic magmas were generated under intense interaction of kimberlitic magmas with the surrounding lithospheric mantle. It may be that during early modification of the lithospheric mantle by kimberlitic magmas as well as with kimberlitic magmas' local stretching and swift ascent, the capture of the mantle xenoliths was favoured over the crystallisation of phenocrysts. The formation of barren kimberlitic magmas may have occurred when the lithospheric mantle in the vicinity of ascending magmas was already geochemically equilibrated with them. It also is possible that the magma's ascent slowed under conditions of dominantly compressive stresses with crystallisation of olivine and other megacrystic phases.
DS202010-1849
2020
Kargin, A.V., Nosova, A.A., Sazonova, L.V., Peresetskaya, E.V., Golubeva, Yu.Yu., Lebedeva, N.M., Tretyachenko, V.V., Khvostikov, V.A., Burmii, J.P.Ilmenite from the Arkangelsk diamond province, Russia: composition, origin and indicator of diamondiferous kimberlites.Petrology, Vol. 28, 4, pp. 315-337. pdfRussia, Archangeldeposit - Grib, Kepino cluster

Abstract: To provide new insights into the origin and evolution of kimberlitic magmas with different diamond concentrations from the Arkhangelsk diamond province in north-western Russia, we examined the major- and trace-element compositions of ilmenite from diamondiferous kimberlite of the Grib pipe and diamond-barren kimberlites from the Kepino cluster (Stepnaya and TsNIGRI-Arkhangelskaya pipes). Ilmenite from diamond-barren kimberlites shows lower Mg, Ti, Cr, Ni and Cu concentrations with increase in both Fe3+ and Fe2+ and Nb, Ta, Zr, Hf, Zn and V concentrations. The main differences between kimberlites with different diamond contents are the Nb and Zr concentrations and their correlation patterns with Mg and Cr concentrations. Ilmenite from the Grib kimberlite has Zr concentrations <110 ppm, whereas ilmenite from the Kepino kimberlites has Zr concentrations >300 ppm. Ilmenite crystallisation within the Grib kimberlite occurred under increasing oxygen fugacity (fO2), which may reflect assimilation of mantle peridotite by the kimberlitic magmas. Ilmenite from the Kepino kimberlites suggests its crystallisation under constant fO2, with the ilmenite composition being controlled by processes of fractional crystallisation of megacrystic minerals. These assumptions were confirmed with assimilation-fractional crystallisation calculations. On the basis of obtained data, we developed a model for the evolution of the kimberlitic magmas for both diamondiferous and barren kimberlites. The diamond-bearing kimberlitic magmas were generated under intense interaction of kimberlitic magmas with the surrounding lithospheric mantle. It may be that during early modification of the lithospheric mantle by kimberlitic magmas as well as with kimberlitic magmas’ local stretching and swift ascent, the capture of the mantle xenoliths was favoured over the crystallisation of phenocrysts. The formation of barren kimberlitic magmas may have occurred when the lithospheric mantle in the vicinity of ascending magmas was already geochemically equilibrated with them. It also is possible that the magma’s ascent slowed under conditions of dominantly compressive stresses with crystallisation of olivine and other megacrystic phases.
DS202003-0344
2019
Katsuke, Y., Sun, Z., Breeding, C.M., Dutrow, B.L.Geographic origin of Paraiba tourmaline.Gems & Gemology, Vol. 55, 4, pp. 648-659.South America, Braziltourmaline

Abstract: Vivid blue to green copper-bearing tourmalines, known as Paraíba tourmalines, are recovered from deposits in Brazil, Nigeria, and Mozambique. These tourmalines are sought after for their intense colors. Prices are based, in part, on the geographic origin of a stone, and determining provenance is thus an important aspect for Paraíba tourmaline. However, their geographic origin cannot be established by standard gemological testing and/or qualitative chemical analyses. GIA has established sophisticated criteria requiring quantitative chemical analyses to determine geographic origin for these tourmalines. These criteria were based on several hundred samples from known sources spanning the three countries. Highly accurate and precise quantitative elemental concentrations for Cu, Zn, Ga, Sr, Sn, and Pb are acquired with laser ablationinductively coupled plasmamass spectrometry (LA-ICP-MS). These data can then be plotted as a function of elemental concentration for accurate geographic origin determination.
DS202005-0741
2020
Keller, D., Ague, J.J.Quartz, mica, and amphibole exsolution from majoritic garnet reveals ultra-deep sediment subduction, Appalachian region.Science Advances, doi. 10.1126/sciadv.aay5178 13p. PdfUnited States, ConnecticutUHT, HPG

Abstract: Diamond and coesite are classic indicators of ultrahigh-pressure (UHP; ?100-kilometer depth) metamorphism, but they readily recrystallize during exhumation. Crystallographically oriented pyroxene and amphibole exsolution lamellae in garnet document decomposed supersilicic UHP majoritic garnet originally stable at diamond-grade conditions, but majoritic precursors have only been quantitatively demonstrated in mafic and ultramafic rocks. Moreover, controversy persists regarding which silicates majoritic garnet breakdown produces. We present a method for reconstructing precursor majoritic garnet chemistry in metasedimentary Appalachian gneisses containing garnets preserving concentric zones of crystallographically oriented lamellae including quartz, amphibole, and sodium phlogopite. We link this to novel quartz-garnet crystallographic orientation data. The results reveal majoritic precursors stable at ?175-kilometer depth and that quartz and mica may exsolve from garnet. Large UHP terranes in the European Caledonides formed during collision of the paleocontinents Baltica and Laurentia; we demonstrate UHP metamorphism from the microcontinent-continent convergence characterizing the contiguous and coeval Appalachian orogen.
DS202004-0522
2020
Kellett, D.A., Pehrsson, S., Skipton, D., Regis, D., Camacho, A., Schneider, D., Berman, R.Thermochronological history of the Northern Canadian Shield. Nuna, Churchill Province, Trans-Hudson orogen, Thelon, RaePrecambrian Research, doi.org/10.1016/j.precamres.2020.105703 in press available 80p. PdfCanadageothermometry

Abstract: The northern Canadian Shield is comprised of multiple Archean cratons that were sutured by the late Paleoproterozoic to form the Canadian component of supercontinent Nuna. More than 2000 combined K-Ar and 40Ar/39Ar cooling ages from across the region reveal a stark contrast in upper and lower plate thermal responses to Nuna-forming events, with the Churchill Province in particular revealing near complete thermal reworking during the late Paleoproterozoic. We review the detailed cooling history for five regions that span the Churchill Province and Trans-Hudson orogen (THO): Thelon Tectonic Zone, South Rae, Reindeer Zone, South Hall Peninsula, and the Cape Smith Belt. The cooling patterns across Churchill Province are revealed in two >1500 km transects. At the plate scale, Churchill’s cooling history is dominated by THO accretionary and collisional events, during which it formed the upper plate. Cooling ages generally young from west to east across both southern and central Churchill, and latest cooling in the THO is 50 myr older in southernmost Churchill (Reindeer Zone) compared to eastern Churchill (Hall Peninsula), indicating diachronous thermal equilibration across 2000 km strike length of the THO. Churchill exhibits relatively high post-terminal THO cooling rates of ~4 °C/myr, which support other geological evidence for widespread rapid exhumation of the THO upper plate following terminal collision, potentially in response to lithospheric delamination.
DS202001-0023
2019
Kelley, S.E., Ross, M., Elliott, B., Normandeau, P.X.Effect of shifting ice flow and basal topography in shaping three dimensional dispersal patterns , Lac de Gras region, Northwest Territories.Journal of Geochemical Exploration, Vol. 199, pp. 105-127.Canada, Northwest Territoriesgeomorphology

Abstract: Tracing indicator minerals and geochemical pathfinders in glacial sediments back to their up-ice source is a common mineral exploration approach in prospective, formerly glaciated regions. In this study, we utilize surface and subsurface data from the Lac de Gras area of the Northwest Territories to develop a three-dimensional understanding of till compositional anomalies emanating from two known kimberlite pipes, DO-18 and DO-27. Specifically, this study examines the three-dimensional shape of dispersal trains as defined by geochemical pathfinder elements and kimberlite indicator minerals shed from a pair of kimberlite pipes within a till cover of variable thickness. From our ninety-four reverse circulation boreholes (n?=?251 till samples), and other publicly-available geologic datasets, we have reconstructed bedrock topography, till thickness, and the subsurface geometry of two dispersal trains. Utilizing our three-dimensional dataset, we have documented the role of basal topography in creating dispersal patterns with contrasting geometries from two adjacent kimberlites, as well as in the preferential preservation of older till units. The combination of field observations of ice-flow indicators and till compositional data demonstrates that features produced by multiple ice flows are preserved in both the erosional and depositional records in this region. Three-dimensional dispersion patterns of kimberlite indicators reflect the effect of shifting ice-flow direction with respect to slope aspect of bedrock topography in governing compositional variability within glacial drift. Our findings suggest that surficial data do not capture the full extent of dispersion patterns even in areas of relatively thin and discontinuous till cover.
DS202006-0925
2016
Kendall, J-M., Lithgow-Bertelloni, C.Why is Africa rifting? GSL SP 420 ( Lyell release May 11, 2020), Vol. 420, pp. 11-30. pdfAfricaTectonics

Abstract: Continental rifting has a fundamental role in the tectonic behaviour of the Earth, shaping the surface we live on. Although there is not yet a consensus about the dominant mechanism for rifting, there is a general agreement that the stresses required to rift the continental lithosphere are not readily available. Here we use a global finite element model of the lithosphere to calculate the stresses acting on Africa. We consider the stresses induced by mantle flow, crustal structure and topography in two types of models: one in which flow is exclusively driven by the subducting slabs and one in which it is derived from a shear wave tomographic model. The latter predicts much larger stresses and a more realistic dynamic topography. It is therefore clear that the mantle structure beneath Africa plays a key part in providing the radial and horizontal tractions, dynamic topography and gravitational potential energy necessary for rifting. Nevertheless, the total available stress (c. 100 MPa) is much less than that needed to break thick, cold continental lithosphere. Instead, we appeal to a model of magma-assisted rifting along pre-existing weaknesses, where the strain is localized in a narrow axial region and the strength of the plate is reduced significantly. Mounting geological and geophysical observations support such a model.
DS202005-0742
2020
Keshav, S., Corgne, A., Gudfinnsson, G.H., Fei, Y.Major and trace element partitioning between majoritic garnet, clinopyroxene, and carbon dioxide-rich liquid in model carbonated peridotite at 10 Gpa and interpretations of the element chemistry of majoritic garnet inclusions in diamonds from the subcontiLithos, Vol. 362-363, 11p. PdfSouth America, Brazil, Guineadiamond inclusions

Abstract: Experimentally determined major and trace element partition coefficients between majoritic garnet, clinopyroxene, and carbon dioxide-rich liquid are reported at 10 GPa and 1800 °C in a model carbonated peridotite composition in the system CaO-MgO-Al2O3-SiO2-CO2. Besides majoritic garnet, the liquid coexists with forsterite, orthopyroxene, and clinopyroxene, making melting phase relations invariant at fixed pressure and temperature conditions. Partition coefficients span a wide range of values - for instance, Sr, Nb, Ba, La, and Ce are highly incompatible in majoritic garnet, while Ca, Y, Nb, and Ho are moderately incompatible, and Lu, Si, Al, and Mg are compatible. Strong fractionation of light rare earth elements (e.g., La, Ce, Nd, Sm) and high field strength elements (e.g., Nb, Ta, Zr, Hf, Th) is seen between majoritic garnet and liquid. The experimentally determined partitioning values are used to calculate compositions of melts in equilibrium with majoritic garnet inclusions in diamonds from select localities in Brazil and Guinea. The calculated melts largely straddle those between documented carbonatites, kimberlites, and alkali basalts, low-degree mantle melting products from carbonated peridotite. This resemblance firmly suggests that majoritic garnet inclusions in diamonds from Brazil and Guinea can simply be interpreted as precipitates from such melts, thereby offering an alternative to the hypothesis that the element chemistry of such inclusions in diamonds can largely, and sometimes only, be ascribed to subducted oceanic crust, and further that, fusion of this crust may limit the terrestrial 'carbon recycling' at depths much beyond corresponding to those of Earth's transition zone.
DS202006-0926
2020
Keulen, N., Thomsen, T.B., Schumacher, J.C., Poulsen, M.D., Kalvig, P., Vennemann, T., Salimi, R.Formation, origin and geographic typing of corundum ( ruby and pink sapphire) from the Fiskenaesst complex, Greenland.Lithos, Vol. 366-367, 26p. PdfEurope, Greenlandruby

Abstract: Metamorphic petrology observations on rubies found in-situ in their host-rock are combined with geochemical measurements and optical microscopy observations on the same rubies, with the aim of connecting the ruby-forming metamorphic reaction to a unique fingerprint for these minerals. The Fiskenæsset complex in Greenland is used as an area of this case study. Isochemical pressure-temperature sections were calculated based on electron microprobe and whole-rock geochemistry analyses, and compared to field observations. Rubies formed from reaction between olivine/serpentine and anorthite, triggered by the intrusion of a 2.71 Ga pegmatite. Al is sourced from the anorthite reacting to calcic amphibole, silica from the pegmatite reacts with olivine/serpentine to anthophyllite, Cr3+ is mobile in the pegmatitic fluid, giving colour to the rubies. The ruby-forming reaction occurs at about 640 °C and 7 kbar. In order to establish the unique fingerprint for this ruby-bearing ultramafic complex, laser-ablation inductively-coupled-plasma mass-spectrometry trace-element measurements, oxygen isotope compositions, optical microscopy and scanning electron microscopy were applied. Due to the setting in an ultramafic rock-anorthosite-leucogabbro complex, the fingerprint of the rubies from the Fiskenæsset complex is rather unique. Compared to rubies from other localities, Fiskenæsset complex rubies contain high Cr, intermediate Fe, and low V, Ga, and Ti concentrations, low oxygen isotope values (1.6-4.2‰) and a rarely-observed combination of optical growth features and mineral inclusions like anthophyllite+biotite. Results for other Greenland localities are presented and discussed as well. Even though these are derived from ultramafic rock settings too, they record different trace-element ratios and oxygen isotope values, resulting from variations in the Archaean ruby-forming reaction.
DS202004-0523
2020
Kibikas, W.M., Carpenter, B.M., Ghassemi, A.Mechanical strength and physical properties of Oklahoma's igneous basement.Tectonophysics, Vol. 777, 228336, 15p. PdfUnited States, Oklahomageophysics, seismics

Abstract: From 2009 to 2016, a drastic increase in seismic activity occurred in the Central and Eastern US (CEUS), particularly in the Oklahoma-Kansas region. The majority of hypocenters were focused in the crystalline basement rock. Information regarding the physical properties (elastic wave velocity, peak strength, etc.) of rocks in the CEUS basement to date is sparse. Forecasting future seismic hazard and predicting the in situ response of the crystalline basement requires their geomechanical parameters be adequately constrained. This work assesses the mechanical and petrophysical properties of several sets of basement rocks from Oklahoma to provide a better framework for understanding intraplate seismicity and overall basement deformation in the continental United States. Laboratory experiments were conducted with granite, rhyolite and diabase basement rock samples collected from southern Oklahoma. Evolution of compressional and shear wave velocity with increasing confinement was measured through a series of ultrasonic velocity tests. A suite of uniaxial and triaxial tests were conducted to measure the elastic and inelastic deformation behavior of the basement rocks. Deformation data was evaluated using the Mohr-Coulomb criterion and compared with additional preexisting deformation data of igneous basement rocks. Dynamic and static elastic properties compare favorably with available field measurements and demonstrate the role physical properties can play in varying mechanical behavior. Granitic samples demonstrate moderate variation of intrinsic physical properties can alter elastic properties and failure behavior significantly. Water-weakening in the basement rocks may indicate fluid-assisted processes such as stress corrosion cracking enhance deformation in the crystalline basement.
DS202011-2047
2020
Kilgore, M.L., Peslier, A.H., Brandon, A.D., Schaffer, L.A., Morris, R.V., Graff, T.G., Agresti, D.G., O'Reilly, S.Y., Griffin, W.L., Pearson, D.G., Barry, K.G., Shaulis, J.Metasomatic control of hydrogen contents in the layered cratonic mantle lithosphere sampled by Lac de Gras xenoliths in the central Slave Craton, Canada.Geochimica et Cosmochimica Acta, Vol. 286, pp. 29-83. pdfCanada, Northwest Territoriesxenoliths

Abstract: Whether hydrogen incorporated in nominally anhydrous mantle minerals plays a role in the strength and longevity of the thick cratonic lithosphere is a matter of debate. In particular, the percolation of hydrogen-bearing melts and fluids could potentially add hydrogen to the mantle lithosphere, weaken its olivines (the dominant mineral in mantle peridotite), and cause delamination of the lithosphere's base. The influence of metasomatism on hydrogen contents of cratonic mantle minerals can be tested in mantle xenoliths from the Slave Craton (Canada) because they show extensive evidence for metasomatism of a layered cratonic mantle. Minerals from mantle xenoliths from the Diavik mine in the Lac de Gras kimberlite area located at the center of the Archean Slave craton were analyzed by FTIR for hydrogen contents. The 18 peridotites, two pyroxenites, one websterite and one wehrlite span an equilibration pressure range from 3.1 to 6.6 GPa and include samples from the shallow (?145?km), oxidized ultra-depleted layer; the deeper (?145-180?km), reduced less depleted layer; and an ultra-deep (?180?km) layer near the base of the lithosphere. Olivine, orthopyroxene, clinopyroxene and garnet from peridotites contain 30-145, 110-225, 105-285, 2-105?ppm H2O, respectively. Within each deep and ultra-deep layer, correlations of hydrogen contents in minerals and tracers of metasomatism (for example light over heavy rare-earth-element ratio (LREE/HREE), high-field-strength-element (HFSE) content with equilibration pressure) can be explained by a chromatographic process occurring during the percolation of kimberlite-like melts through garnet peridotite. The hydrogen content of peridotite minerals is controlled by the compositions of the evolving melt and of the minerals and by mineral/melt partition coefficients. At the beginning of the process, clinopyroxene scavenges most of the hydrogen and garnet most of the HFSE. As the melt evolves and becomes enriched in hydrogen and LREE, olivine and garnet start to incorporate hydrogen and pyroxenes become enriched in LREE. The hydrogen content of peridotite increases with decreasing depth, overall (e.g., from 75 to 138?ppm H2O in the deep peridotites). Effective viscosity calculated using olivine hydrogen content for the deepest xenoliths near the lithosphere-asthenosphere boundary overlaps with estimates of asthenospheric viscosities. These xenoliths cannot be representative of the overall cratonic root because the lack of viscosity contrast would have caused basal erosion of lithosphere. Instead, metasomatism must be confined in narrow zones channeling kimberlite melts through the lithosphere and from where xenoliths are preferentially sampled. Such localized metasomatism by hydrogen-bearing melts therefore does not necessarily result in delamination of the cratonic root.
DS202007-1155
2020
Kim, D.Seismic echoes reveal structures at the base of the mantle.www.livescience.com/core-mantle-ULVZ-blobs-enormous.html, 3p. Mantlegeophysics - seismics
DS202003-0345
2020
King, S.D.Do impacts impact global tectonics?Geology, Vol. 48, pp. 205-206. Globalgeodynamics
DS202011-2048
2020
Kiraly, A., Conrad, C.P., Hansen, L.N.Evolving viscous anisotropy in the Upper mantle and its geodynamic implications.Geochemistry, Geophysics, Geosystems, 10.1029/ 2020GC009159 22p. PdfMantleolivine

Abstract: The uppermost layer of Earth's mantle, the asthenosphere, experiences large deformations due to a variety of tectonic processes. During deformation, grains of olivine, the main rock?forming mineral in the asthenosphere, rotate into a preferred direction parallel to the deformation, developing a texture that can affect the response of the asthenosphere to tectonic stresses. Laboratory measurements show that the deformation rate depends on the orientation of the shear stress relative to the olivine texture. We use numerical models to apply the findings of the laboratory measurements to geodynamic situations that are difficult to simulate in a laboratory. These models track the development of olivine texture and its directional response to shear stress, which are highly coupled. Our results suggest that anisotropic viscosity in the asthenosphere can significantly affect the motions of tectonic plates, as plate motion in a continuous direction should become faster, while abrupt changes in the direction of plate motion should meet high resistance in the underlying asthenosphere. We suggest that olivine textures in the asthenosphere play a critical role in upper mantle dynamics.
DS202008-1408
2019
Kirkpatrick, S., Mukendwa, J.Operational changes enable Namdeb's Southern Coastal mining team to reduce risk and increase productivity as we advance deeper into the Atlantic Ocean.The Journal of the Southern African Insitute of Mining and Metallurgy, Vol. 119, Feb. 8p. PdfAfrica, Namibiadeposit - Southern Coastal

Abstract: The mining operation at Namdeb's Southern Coastal Mine (SCM) is unique. It targets gravel layers up to 30 m below sea level, which continue to dip deeper, further west, under the Atlantic Ocean. On this storm-dominated coastline, severe water seepage into mining areas, rugged orebody footwall characteristics, and highly variable resource grades all contribute to a challenging operational environment. Namdeb has a proud history of innovation, and as the mine progresses further westwards and associated technical and economic challenges increase, this innovative culture has become essential to the future of the mine. The Theory of Constraints (ToC) has been widely used at SCM, and across the mining discipline, to focus efforts on improving overall business profitability. Through analysis of the mining processes, opportunities were identified, solutions developed, and initiatives implemented with staggering results across all three mining disciplines, i.e. stripping, load and haul, and bedrock bulking and cleaning. This paper outlines the solutions adopted and the results of the ToC analysis.
DS202010-1850
2020
Kiseeva, E.S., Yuzmukhametov, R.N.Women at the dawn of diamond discovery in Siberia or how two women discovered the Siberian diamond province. Popugaeva and SarsadskhihBurek, C.V., Higgs, B. eds Celebrating 100 years of female fellowship of the Geological Society: Discovering forgotten histories. Geological Society of London Special Publ. 506, in press, 13p. PdfRussia, Siberiahistory

Abstract: Exploration for diamonds in the Soviet Union started in the 1940s, however it was not until the beginning of 1950s that the government acknowledged a strong need for locally mined diamonds. In this article, based on publications from Russian literature, we recount a story of two female geologists, Larisa Popugaeva and Natalia Sarsadskhih. Natalia was the head of the mineralogical laboratory who implemented a new methodology to search for mineral indicators of primary diamond deposits. Larisa was a young geologist who joined Natalia's team in 1953. The work of these women led to the discovery in 1954 of the first diamond deposit in the country - a kimberlite pipe "Zarnitsa". In 1954 Natalia was unable to go into the field, therefore the discovery was made by Larisa. Credit for this discovery, however, was claimed by the higher officials from the Amakinskaya expedition, one of the largest diamond exploration organisations in the country. Multiple efforts to restore justice did not succeed, with Larisa only being awarded the title of the "Discoverer" in 1970, and Natalia not until 1990. This article provides a description of Larisa's and Natalia's life up until the discovery of Zarnitsa, and a few significant events after.
DS202008-1409
2020
Klashnikova, T.V., Soloveva, L.V., Kostrovitsky, S.I., Sun, J.Geochemical features of peridotite xenolith from Obnazhennaya kimberlite pipe - cumulates or residues?Goldschmidt 2020, 1p. AbstractRussiadeposit - Obnazhennaya

Abstract: This study concerns the geochemical characteristics of mantle xenoliths from the upper-Jurassic Obnazhennaya kimberlite pipe (Kuoika field, Yakutian kimberlite province, the north-east of Siberian craton). The so-called magnesian xenolith group (Sp, Sp-Grt, Grt lherzolites, olivine websterites and websterites) was distinguished, the rocks of the group are assumed to be of the same genesis based on transitions in modal mineral composition and a change in the composition of minerals. The chemical composition (CaO, MgO) of most depleted harzburgites, as well as part of the lherzolites of the magnesian group coincide with the restites obtained by experimental melting, which suggested their residue origin. Narrow variations in the composition of olivine (Mg # - 91-92; NiO - 0.35-0.45 wt.%) and orthopyroxene (Mg # - 92-93) for Obnazhennaya peridotites also support this hypothesis. In terms of chemical composition, olivines coincide with the “mantle trend” of olivines from the lithospheric mantle. Nevertheless, garnets from the peridotites consistently change their composition in the direction of decreasing Cr2O3, CaO and Mg # values from Grt, Sp-Grt lherzolites to Grt websterites. The garnet composition from Obnazhennaya peridotites differs from Udachnaya peridotites, for which the residue hypothesis assumed. They are similar in composition to garnets from Beni-Bousera garnet pyroxenites, as well as to garnets from deformed lherzolites of the Udachnaya pipe, which suggests crystallization of garnets from the melt and the effect of metasomatic processes. The formation of orogenic massifs is a multi-stage process, many authors suggest that pyroxenite veins in mafic complexes are cumulative in origin and show signs of metasomatic processes (in particular, enrichment with aluminum, calcium and chromium, increased REE concentrations in garnet). So peridotite cumulative origin and further metasomatic transformations were suggested.
DS202002-0195
2020
Klaver, M., Ionov, D.A., Takazawa, E., Elliott, T.The non-chondritic Ni isotope composition of Earth's mantle.Geochimica et Cosmochimica Acta, Vol. 268, pp. 405-421.Mantleperidotites

Abstract: Nickel is a major element in the Earth. Due to its siderophile nature, 93% of Ni is hosted in the core and the Ni isotope composition of the bulk silicate Earth might inform on the conditions of terrestrial core formation. Whether Earth’s mantle is fractionated relative to the chondritic reservoir, and by inference to the core, is a matter of debate that largely arises from the uncertain Ni isotope composition of the mantle. We address this issue through high-precision Ni isotope measurements of fertile- to melt-depleted peridotites and compare these data to chondritic meteorites. Terrestrial peridotites that are free from metasomatic overprint display a limited range in ?60/58Ni (deviation of 60Ni/58Ni relative to NIST SRM 986) and no systematic variation with degree of melt depletion. The latter is consistent with olivine and orthopyroxene buffering the Ni budget and isotope composition of the refractory peridotites. As such, the average Ni isotope composition of these peridotites (?60/58Ni = 0.115 ± 0.011‰) provides a robust estimate of the ?60/58Ni of the bulk silicate Earth. Peridotites with evidence for melt metasomatism range to heavier Ni isotope compositions where the introduction of clinopyroxene appears to drive an increase in ?60/58Ni. This requires a process where melts do not reach isotopic equilibrium with buffering olivine and orthopyroxene, but its exact nature remains obscure. Chondritic meteorites have variability in ?60/58Ni due to heterogeneity at the sampling scale. In particular, CI1 chondrites are displaced to isotopically lighter values due to sorption of Ni onto ferrihydrite during parent body alteration. Chondrites less extensively altered than the CI1 chondrites show no systematic differences in ?60/58Ni between classes and yield average ?60/58Ni = 0.212 ± 0.013‰, which is isotopically heavier than our estimate of the bulk silicate Earth. The notable isotopic difference between the bulk silicate Earth and chondrites likely results from the segregation of the terrestrial core. Our observations potentially provide a novel constraint on the conditions of terrestrial core formation but requires further experimental calibration.
DS202010-1851
2020
Klemme, S., Berndt, J.Trace element between pyrochlore, microlite, fersmite and silicate melts.Geochemical Transactions, Vol. 21, 9, 14p. PdfMantlemelting

Abstract: We present experimentally determined trace element partition coefficients (D) between pyrochlore-group minerals (Ca2(Nb,Ta)2O6(O,F)), Ca fersmite (CaNb2O6), and silicate melts. Our data indicate that pyrochlores and fersmite are able to strongly fractionate trace elements during the evolution of SiO2-undersaturated magmas. Pyrochlore efficiently fractionates Zr and Hf from Nb and Ta, with DZr and DHf below or equal to unity, and DNb and DTa significantly above unity. We find that DTa pyrochlore-group mineral/silicate melt is always higher than DNb, which agrees with the HFSE partitioning of all other Ti-rich minerals such as perovskite, rutile, ilmenite or Fe-Ti spinel. Our experimental partition coefficients also show that, under oxidizing conditions, DTh is higher than corresponding DU and this implies that pyrochlore-group minerals may fractionate U and Th in silicate magmas. The rare earth element (REE) partition coefficients are around unity, only the light REE are compatible in pyrochlore-group minerals, which explains the high rare earth element concentrations in naturally occurring magmatic pyrochlores.
DS202006-0927
2020
Ko, B., Prakapenka, V., Kunz, M., Prescher, C., Leinenweber, K., Shim, S-H.Mineralogy and density of Archean volcanic crust in the mantle transition zone.Physics of the Earth and Planetary Interiors, Vol. 305, 13p. PdfMantledensity

Abstract: The composition of Archean volcanic crust can be characterized by a higher Mg/Si ratio than modern mid-ocean ridge basalt (MORB), because of the higher degree melting from the warmer mantle in the Archean. Although modern MORB may become less dense than the surrounding mantle beneath the mantle transition zone (MTZ), the Mg-rich composition of Archean volcanic crust may result in the different density, and therefore different sinking behavior near the MTZ. In order to understand the compositional effect of Archean volcanic crust on the sinking behaviors and the scale of mantle mixing in the Archean, we investigated the mineralogy and density of Archean volcanic crust near the MTZ (470-910 km-depth). We conducted experiments at 19-34 GPa and 1400-2400 K using the laser-heated diamond anvil cell (LHDAC) combined with in-situ X-ray diffraction (XRD). The in-situ XRD and the chemical analysis revealed that Archean volcanic crust forms garnet and ringwoodite (84 and 16 vol%, respectively), which gradually transforms to Brg and CaPv (82 and 18 vol%, respectively) at 23-25 GPa and 1800 K. Our in-situ XRD experiments allowed us to measure the volumes of stable phases and to estimate their densities at high pressure and temperature. The results suggest that Archean volcanic crust maintains greater density than the pyrolitic mantle in the Archean regardless of temperature at 20-34 GPa (570-850 km-depth), promoting further sinking into the deeper mantle in the Archean. We also considered the density of the subducting slab in the Archean. The density model showed that the subducting slab is still denser or at least equally dense as the surrounding pyrolitic mantle in the Archean.
DS202008-1410
2020
Ko, B., Prakapenka, V., Kunz, M., Prescher, C., Leinenweber, K., Shim, S-H.Mineralogy and density of Archean volcanic crust in the mantle transition zone.Physics of the Earth and Planetary Interiors, Vol. 305, 13p. PdfMantlesubduction

Abstract: The composition of Archean volcanic crust can be characterized by a higher Mg/Si ratio than modern mid-ocean ridge basalt (MORB), because of the higher degree melting from the warmer mantle in the Archean. Although modern MORB may become less dense than the surrounding mantle beneath the mantle transition zone (MTZ), the Mg-rich composition of Archean volcanic crust may result in the different density, and therefore different sinking behavior near the MTZ. In order to understand the compositional effect of Archean volcanic crust on the sinking behaviors and the scale of mantle mixing in the Archean, we investigated the mineralogy and density of Archean volcanic crust near the MTZ (470-910 km-depth). We conducted experiments at 19-34 GPa and 1400-2400 K using the laser-heated diamond anvil cell (LHDAC) combined with in-situ X-ray diffraction (XRD). The in-situ XRD and the chemical analysis revealed that Archean volcanic crust forms garnet and ringwoodite (84 and 16 vol%, respectively), which gradually transforms to Brg and CaPv (82 and 18 vol%, respectively) at 23-25 GPa and 1800 K. Our in-situ XRD experiments allowed us to measure the volumes of stable phases and to estimate their densities at high pressure and temperature. The results suggest that Archean volcanic crust maintains greater density than the pyrolitic mantle in the Archean regardless of temperature at 20-34 GPa (570-850 km-depth), promoting further sinking into the deeper mantle in the Archean. We also considered the density of the subducting slab in the Archean. The density model showed that the subducting slab is still denser or at least equally dense as the surrounding pyrolitic mantle in the Archean.
DS202009-1635
2020
Koemets, I., Satta, N., Marquardt, H., Kiseeva, E.S., Kurnosov, A., Stachel, T., Harris, J.W., Dubrovinsky, L.Elastic properties of majorite garnet inclusions in diamonds and the seismic signature of pyroxenites in the Earth's upper mantle.American Mineralogist, Vol. 105, pp. 984-991. pdfMantlediamond inclusions

Abstract: Majoritic garnet has been predicted to be a major component of peridotite and eclogite in Earth's deep upper mantle (>250 km) and transition zone. The investigation of mineral inclusions in diamond confirms this prediction, but there is reported evidence of other majorite-bearing lithologies, intermediate between peridotitic and eclogitic, present in the mantle transition zone. If these lithologies are derived from olivine-free pyroxenites, then at mantle transition zone pressures majorite may form monomineralic or almost monomineralic garnetite layers. Since majoritic garnet is presumably the seismically fastest major phase in the lowermost upper mantle, the existence of such majorite layers might produce a detectable seismic signature. However, a test of this hypothesis is hampered by the absence of sound wave velocity measurements of majoritic garnets with relevant chemical compositions, since previous measurements have been mostly limited to synthetic majorite samples with relatively simple compositions. In an attempt to evaluate the seismic signature of a pyroxenitic garnet layer, we measured the sound wave velocities of three natural majoritic garnet inclusions in diamond by Brillouin spectroscopy at ambient conditions. The chosen natural garnets derive from depths between 220 and 470 km and are plausible candidates to have formed at the interface between peridotite and carbonated eclogite. They contain elevated amounts (12-30%) of ferric iron, possibly produced during redox reactions that form diamond from carbonate. Based on our data, we model the velocity and seismic impedance contrasts between a possible pyroxenitic garnet layer and the surrounding peridotitic mantle. For a mineral assemblage that would be stable at a depth of 350 km, the median formation depth of our samples, we found velocities in pyroxenite at ambient conditions to be higher by 1.9(6)% for shear waves and 3.3(5)% for compressional waves compared to peridotite (numbers in parentheses refer to uncertainties in the last given digit), and by 1.3(13)% for shear waves and 2.4(10)% for compressional waves compared to eclogite. As a result of increased density in the pyroxenitic layer, expected seismic impedance contrasts across the interface between the monomineralic majorite layer and the adjacent rocks are about 5-6% at the majorite-eclogite-interface and 10-12% at the majoriteperidotite-boundary. Given a large enough thickness of the garnetite layer, velocity and impedance differences of this magnitude could become seismologically detectable.
DS202001-0024
2019
Kogarko, L.N., Veselovskiy, R.V.Geodynamic origin of carbonatites from the absolute paleoproterozoic reconstructions. Maymecha-KotuyJournal of Geodynamics, Vol. 125, pp. 13-21.Russia, Siberiacarbonatite

Abstract: Geodynamic origin of carbonatites is debated for several decades. One of hypotheses links their origin to large-volume mantle plumes rising from the core-mantle boundary (CMB). Some evidence exists for temporal and spatial relationships between the occurrences of carbonatites and large igneous provinces (LIPs), and both carbonatites and LIPs can be related to mantle plumes. A good example is the carbonatites of the Maymecha-Kotuy Province in the Polar Siberia, which were formed at the same time as the Siberian superplume event at ca. 250 Ma. In this study we use a recently published absolute plate kinematic modelling to reconstruct the position of 155 Phanerozoic carbonatites at the time of their emplacement. We demonstrate that 69% of carbonatites may be projected onto the central or peripheral parts of the large low shear-wave velocity provinces (LLSVPs) in the lowermost mantle. This correlation provides a strong evidence for the link between the carbonatite genesis and the locations of deep-mantle plumes. A large group of carbonatites (31%) has no obvious links to LLSVPs and, on the contrary, they plot above the "faster-than-average S-wave" zones in the deep mantle, currently located beneath North and Central America and China. We propose that their origin may be associated with remnants of subducted slabs in the mantle.
DS202010-1852
2020
Komarovskikh, A., Rakhmanova, M., Yuryeva, O., Nadolinny, V.Infrared, photoluminescence, and electron paramagnetic resonance characteristic features of diamonds from Aikhal pipe, (Yakutia).Diamond & Related Materials, Vol. 109, 108045, 9p. PdfRussiadeposit - Aikhal

Abstract: The diversity of the defects in the collection (50 samples) of diamonds from the Aikhal pipe (Yakutia) has been studied with IR, PL, and EPR spectroscopy. The specific features of crystals have been established; the obtained information leads to the discussion about the diamond formation and growth conditions. One of the specific features observed is a high concentration of platelets. According to the platelet behavior, most of the crystals are regular suggesting the growth temperature to be 1100-1200 °C. The concentrations of A and B defects have been evaluated and the same temperature conditions have been obtained according to the Taylor diagram. Using the EPR spectroscopy, the C and N3V centers have been found in many crystals suggesting the aggregation of nitrogen during residence in the mantle at high temperatures. An interesting feature has been observed in the PL spectra. For most crystals, the spectrum with ZPL at 563.5 nm is very intensive. The structure of the observed defect is remaining unknown, the spectrum disappears as a result of annealing at 600 °C indicating the interstitial-vacancy annihilation mechanism.
DS202012-2224
2020
Komarovskikh, A., Rakmanova, M., Yuryeva, O., Nadolinny, V.Infrared, photoluminescence, and electron paramagnetic resonance characteristic features of diamonds from the Aikhal pipe ( Yakutia).Diamond and Related Materials, Vol. 109, 108045, 9p. PdfRussiadeposit - Aikhal

Abstract: The diversity of the defects in the collection (50 samples) of diamonds from the Aikhal pipe (Yakutia) has been studied with IR, PL, and EPR spectroscopy. The specific features of crystals have been established; the obtained information leads to the discussion about the diamond formation and growth conditions. One of the specific features observed is a high concentration of platelets. According to the platelet behavior, most of the crystals are regular suggesting the growth temperature to be 1100-1200 °C. The concentrations of A and B defects have been evaluated and the same temperature conditions have been obtained according to the Taylor diagram. Using the EPR spectroscopy, the C and N3V centers have been found in many crystals suggesting the aggregation of nitrogen during residence in the mantle at high temperatures. An interesting feature has been observed in the PL spectra. For most crystals, the spectrum with ZPL at 563.5 nm is very intensive. The structure of the observed defect is remaining unknown, the spectrum disappears as a result of annealing at 600 °C indicating the interstitial-vacancy annihilation mechanism.
DS202007-1156
2020
Koop. F.What's deep sea mining? Risks and challenges of the new industrial frontier…. Mentions diamonds in Namibia.ZMEscience.com, June 24, 6p.Africa, Namibia, Globalmining
DS202007-1157
2020
Korenaga, J.Plate tectonics and surface environment: role of the oceanic upper mantle.Earth Science Reviews, Vol. 205, 103185 22p. PdfMantlegeodynamics

Abstract: Earth is so far the only planet that exhibits plate tectonics, and along with the right heliocentric distance and the presence of surface water, plate tectonics is among necessary conditions for a habitable planet. Yet, the physics of this particular style of mantle convection is poorly understood, creating a substantial bottleneck in developing the general theory of planetary evolution. As plate tectonics is characterized by the subduction of oceanic lithosphere, a better understanding of the oceanic upper mantle could potentially help to break this stalemate. In this review, I summarize available theoretical, observational, and experimental constraints on the evolution of the oceanic upper mantle and its rheology, place the study of the oceanic upper mantle in the big picture of Earth evolution, and provide some suggestions for future research in relevant disciplines, including marine geophysics and computational geodynamics.
DS202008-1411
2020
Korneeva, A.A., Nikolai, N.A., Kamenetsky, V.S., Portnyagin, M.V., Savelyev, D.P., Krasheninnikov, S.P., Abersteiner, A., Kamenetsky, M.B., Zelenski, M.E., Shcherbakov, V.D., Botcharnikov, R.E.Composition, crystallization conditions and genesis of sulfide saturated parental melts of olivine-phyric rocks from Kamchatsky Mys ( Kamchatka, Russia).Lithos, 10.1016/j.lithos.2020.105657Russia, Kamchatkapicrites

Abstract: Sulfide liquids that immiscibly separate from silicate melts in different magmatic processes accumulate chalcophile metals and may represent important sources of the metals in Earth's crust for the formation of ore deposits. Sulfide phases commonly found in some primitive mid-ocean ridge basalts (MORB) may support the occurrence of sulfide immiscibility in the crust without requiring magma contamination and/or extensive fractionation. However, the records of incipient sulfide melts in equilibrium with primitive high-Mg olivine and Cr-spinel are scarce. Sulfide globules in olivine phenocrysts in picritic rocks of MORB-affinity at Kamchatsky Mys (Eastern Kamchatka, Russia) represent a well-documented example of natural immiscibility in primitive oceanic magmas. Our study examines the conditions of silicate-sulfide immiscibility in these magmas by reporting high precision data on the compositions of Cr-spinel and silicate melt inclusions, hosted in Mg-rich olivine (86.9-90 mol% Fo), which also contain globules of magmatic sulfide melt. Major and trace element contents of reconstructed parental silicate melts, redox conditions (?QFM = +0.1 ± 0.16 (1?) log. units) and crystallization temperature (1200-1285 °C), as well as mantle potential temperatures (~1350 °C), correspond to typical MORB values. We show that nearly 50% of sulfur could be captured in daughter sulfide globules even in reheated melt inclusions, which could lead to a significant underestimation of sulfur content in reconstructed silicate melts. The saturation of these melts in sulfur appears to be unrelated to the effects of melt crystallization and crustal assimilation, so we discuss the reasons for the S variations in reconstructed melts and the influence of pressure and other parameters on the SCSS (Sulfur Content at Sulfide Saturation).
DS202006-0928
2020
Korsakov, A.V., Kohn, M.J., Perraki, M.Applications of raman spectroscopy in metamorphic petrology and tectonics. ( mentions diamond)Elements, Vol. 16, pp. 105-110.Mantlespectroscopy, geothermalbarometry

Abstract: Raman spectroscopy is widely applied in metamorphic petrology and offers many opportunities for geological and tectonic research. Minimal sample preparation preserves sample integrity and microtextural information, while use with confocal microscopes allows spatial resolution down to the micrometer level. Raman spectroscopy clearly distinguishes mineral polymorphs, providing crucial constraints on metamorphic conditions, particularly ultrahigh-pressure conditions. Raman spectroscopy can also be used to monitor the structure of carbonaceous material in metamorphic rocks. Changes in structure are temperature-sensitive, so Raman spectroscopy of carbonaceous material is widely used for thermometry. Raman spectroscopy can also detect and quantify strain in micro-inclusions, offering new barometers that can be applied to understand metamorphic and tectonic processes without any assumptions about chemical equilibrium.
DS202002-0196
2020
Kostrovitsky, S.I., Yakolev, D.A.The origin of salts in unaltered kimberlites. Comment on Abersteiner article Journal of Petrology, in press available, 13p.Russiadeposit - Udachnaya-East

Abstract: The article by Abersteiner et al., (2018) discussing the mantle origin of salts in serpentine-free kimberlites from the Udachnaya-East pipe contradicts the views of Kostrovitsky et al. (2013) concerning the origin of these salts from a surface source of brines. Here we wish to emphasize that Abersteiner et al. (2018) have presented erroneous statements regarding the genesis of these rocks. On the basis of the data collected by hydrogeologists working at Udachnaya-East we consider that unaltered kimberlites occur at 400-500 m depth, where the brines precipitated salts. The relation of unaltered kimberlites to the surface sources of salt is illustrated by the cross sections of the Mir and International’naya pipes, where serpentine-free kimberlites occur at the depths of Cambrian evaporite host rocks intercalated with thick halite layers. It is assumed that the salts from surface sources prevented olivine serpentinization. The secondary origin of salts in serpentine-free kimberlites is confirmed by our investigations and the hypothesis regarding the mantle origin of salts is doubtful.
DS202005-0743
2020
Kostrovitsky, S.I., Yakolev, D.A., Soltys, A., Ivanov, A.S., Matsyuk, S.S., Robles-Cruz, S.E.A genetic relationship between magnesian ilmenite and kimberlites of the Yakutian diamond fields.Ore Geology Reviews, Vol. 120, 16p. PdfRussia, Yakutiailmenite

Abstract: We present new major element geochemical data, and review the existing data for ilmenite macrocrysts, megacrysts, as well as ilmenite in mantle xenoliths from four diamondiferous kimberlite fields in the Yakutian province. This combined data set includes 10,874 analyses of ilmenite from 94 kimberlite pipes. In the studied samples we identify various different ilmenite compositional distributions (e.g., “Haggerty's parabola”, or “Step-like” trends in MgO-Cr2O3 bivariate space), which are common to all kimberlites from a given cluster, but the compositional distributions differ between clusters. We propose three stages of ilmenite crystallization: 1) Mg-Cr poor ilmenite crystallising from a primitive asthenospheric melt (the base of Haggerty's parabola on MgO-Cr2O3 plots). 2) This primitive asthenospheric melt was then modified by the partial assimilation of lithospheric material, which enriched the melt in MgO and Cr2O3 (left branch of Haggerty’s parabola). 3) Ilmenite subsequently underwent sub-solidus recrystallization in the presence of an evolved kimberlite melt under increasing oxygen fugacity (ƒO2) conditions (right branch of Haggerty’s parabola in MgO-Cr2O3 plots). Significant differences in the ilmenite compositional distribution between different kimberlite fields are the result of diverse conditions during subsequent ilmenite crystallization in a kimberlite melt ascending through the lithospheric mantle, which have different textures and compositions beneath the studied kimberlite fields. We propose that a TiO2 fluid formed due to immiscibility of an asthenospheric melt with low Cr and high Ti contents. This fluid infiltrated lithospheric mantle rocks forming Mg-ilmenite. These features indicate a genetic link between ilmenite and the host kimberlite melt.
DS202009-1636
2019
Kozenko, J.A song of ice and diamonds. Alrosa …. Challenging landscapes… Gems & Jewellery, Vol. 29, 3, autumn pp. 29-31.Russia, Yakutia Arkhanelskhistory
DS202002-0197
2019
Krebs, M.Y., Pearson, D.G., Fagan, A.J., Bussweiler, Y., Sarkar, C.The application of trace elements and Sr-Pb isotopes to dating and tracing ruby formation: the Aappaluttoq deposit, SW Greenland.Chemical Geology, Vol. 523, pp. 42-58.Europe, Greenlandruby

Abstract: Trace element characteristics of rubies from the Aappaluttoq deposit, SW Greenland, were measured using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), laser ablation - inductively coupled plasma-time of flight-mass spectrometry (LA-ICP-TOF-MS) and offline laser ablation followed by solution ICP-MS. LA-ICP-TOF-MS - applied to rubies for the first time - effectively maps trace element spatial variation in these gems. With the exception of a small number of elements that can substitute for Al3+ in the crystal structure (e.g., Ti, Fe, V, Cr, Mg), trace element mapping clearly demonstrates that most elements such as Th, U, Sr and Rb are hosted in mineral and fluid inclusions or are present along fractures. Primitive mantle normalized trace element patterns show characteristics that are broadly correlative to mineral inclusions within the analysed rubies. These minerals include rutile (enrichment of HFSE over LREE, high Ta/Nb and Hf/Zr ratios and low Th/U ratios), phlogopite (enrichment in Rb and Ba and positive Sr anomalies), and zircon (extreme enrichment in Zr-Hf, U and Th, HREE enrichment over LREE and positive Ce anomalies). The sample suite analysed here is derived from a bulk sample of ore composed of three different rock types (sapphirine-gedrite, leucogabbro and phlogopitite). Two different populations of ruby were identified at Aappaluttoq; these can be defined on the basis of their different V content within the corundum lattice. Therefore, V content may be able to geochemically define rubies from different host rocks within the same deposit. Using offline laser ablation followed by thermal ionization mass spectrometry (TIMS) we measured the radiogenic isotope compositions in ruby for the first time. A Pb-Pb isochron age of 2686 +300/?74?Ma, was defined for gem formation at Aappaluttoq. We believe that this is the first ever direct age determined on a ruby suite, independent of associated minerals, derived by bulk sampling sub-micron to micron sized inclusions in the corundum lattice. This age likely reflects the re-crystallization and re-setting of the ruby (and its U-Pb system) during the Neoarchean in SW Greenland, due to regional granulite to upper-amphibolite facies metamorphism.
DS202006-0929
2020
Krishnamurthy, P.Rare metal (RM) and rare earth element ( REE) resources: world scenario with special reference to India.Journal of the Geological Society of India, Vol. 95, pp. 464-474.India, globalREE

Abstract: The RM (Li, Be, Ti, Zr, Nb, Ta, Th and U) and REE (Light Rare Earths and Heavy Rare Earths including Yttrium) are strategic and critical for sustaining a variety of industries such as nuclear, defence, information technology (IT) and green energy options (wind, solar, electric vehicles and others). The 2010 ‘Rare Earth’ crisis of the world, following China’s monopoly with over 80% share and export restrictions in the REE market, led to an exploration boom for REE all over the world including India. This led to a substantial increase in REE mineral resources (98 Mt of contained REO in 2015) outside China located in Canada (38 Mt), Greenland (39 Mt) and Africa (10.3 Mt) that represents a fivefold increase in resources (c.f. Paulick and Machacek, 2017). As per the 2019, USGS commodity survey, the world reserves of REE have been estimated at 120 Mt in countries such as China (44Mt), Brazil (22Mt), Vietnam (22 Mt), Russia (12 Mt), India (6.9 Mt) and others (13 Mt). At present world resources of RM and REE are adequate to cater the demands of the different industries. The constraints, however, appear to be not technical but mainly environmental and social issues.
DS202003-0346
2020
Krmicek, L., Ackerman, L., Hruby, J., Kynicky, J.The highly siderophile elements and Re-Os isotope geochemistry of Variscan lamproites from the Bohemian Massif: implications for regionally dependent metasomatism of orogenic mantle.Chemical Geology, Vol. 532, 11p. Available pdfEurope, Czech republic, Austria, Polandlamproites

Abstract: Orogenic lamproites represent a group of peralkaline, ultrapotassic and perpotassic mantle-derived igneous rocks that hold the potential to sample components with extreme compositions from highly heterogeneous orogenic mantle. In our pilot study, we present highly siderophile element (HSE) and ReOs isotope systematics of Variscan orogenic lamproites sampled in the territories of the Czech Republic, Austria and Poland, i.e., from the termination of the Moldanubian and Saxo-Thuringian zones of the Bohemian Massif. Orogenic lamproites of the Bohemian Massif are distinguished by variably high contents of SiO2, high Mg# and predominant mineral associations of K-rich amphibole and Fe-rich microcline. The HSE show (i) consistently very low contents in all investigated orogenic lamproites compared to the estimated concentrations in majority of mid-ocean ridge basalts, hotspot-related volcanic rocks (e.g., ocean island basalts, continental flood basalts, komatiites, some intraplate alkaline volcanic rocks such as kimberlites and anorogenic lamproites) and arc lavas, and (ii) marked differences in relative and absolute HSE abundances between the samples from the Moldanubian and Saxo-Thuringian Zone. Such a regional dependence in HSE from mantle-derived melts is exceptional. Orogenic lamproites have highly variable and high initial suprachondritic 187Os/188Os values (up to 0.631) compared with rather chondritic to subchondritic Os isotope values of the young lithospheric mantle below the Bohemian Massif. The highly radiogenic Os isotope component in orogenic lamproites may be derived from preferential melting of metasomatised vein assemblages sitting in depleted peridotite mantle. This process appears to be valid generally in the petrogenesis of orogenic lamproites both from the Bohemian Massif and from the Mediterranean area. As a specific feature of the orogenic lamproites from the Bohemian Massif, originally ultra-depleted mantle component correlative with remnants of the Rheic Ocean lithosphere in the Moldanubian Zone was metasomatised by a mixture of evolved and juvenile material, whereas the lithospheric mantle in the Saxo-Thuringian Zone was enriched through the subduction of evolved crustal material with highly radiogenic Sr isotope signature. As a result, this led to observed unique regionally dependent coupled HSE, RbSr and ReOs isotope systematics.
DS202009-1637
2020
Krmicek, L., Romer, R.L., Cempirek, J., Gadas, P., Krmickova, S., Glodny, J.Petrographic and Sr-Nd-Pb-Li isotope characteristics of a complex lamproite intrusion from the Saxo-Thuringian zone: a unique example of peralkaline mantle-derived melt differentiation.Lithos, Vol. 374-375, 15p. PdfEurope, Bohemian Massiflamproites

Abstract: Variscan orogenic lamproites in the Bohemian Massif predominantly occur as 1 to 2?m wide and petrographically uniform dykes along the eastern borders of the Moldanubian and Saxo-Thuringian zones. Variscan orogenic lamproites were derived by preferential melting of subduction-related olivine-free metasomatic vein assemblages stabilised in the lithospheric mantle. These lamproitic melts may subsequently undergo extensive differentiation. In this study, we present the first combined petrographic and Sr-Nd-Pb-Li isotope characteristics of a complex lamproite exposed at ca 100?m long profile near Horní Rokytnice (Czech Republic) in the Saxo-Thuringian Zone. This lamproite is characterised by the primary mineral assemblage of K-amphibole + K-feldspar ± aegirine and quartz that petrographically varies from relatively primitive (fine-grained, mafic) to more differentiated (medium- to coarse-grained, felsic) pegmatitic lamproite domains. These domains may represent the product of crystallisation of immiscible liquids that had separated from the mafic melt. The primitive lamproite zone is characterised by the typomorphic minerals - baotite, benitoite, and henrymeyerite. The more differentiated pegmatitic domains are free of aegirine and show replacement of primary red-luminescent (Fe3+-rich) K-feldspar by blue-luminescent (Fe-poor) K-feldspar. Residual fluids rich in Ca, Ti, and HFSE in combination with the decreasing peralkalinity of the lamproite system resulted in the local formation of secondary zircon, titanite and quartz at the expense of the primary Ti-Ba-Zr-K lamproitic mineral assemblages. Lamproites from the Moldanubian and Saxo-Thuringian zones fall on separate mixing trends in the 87Sr/86Sr(t) - ?Nd(t) diagram, which indicates that the mantle beneath these two zones had been metasomatised by different crustal material. The scatter in the peralkalinity index vs. ?7Li diagram indicates that the Li isotope composition is not controlled by mixing of two end members metasome and ambient depleted mantle alone, but may also be affected by late-stage magmatic and hydrothermal processes. The compositionally zoned Horní Rokytnice dyke is special as the petrographically different types show a variation of about 4 ?-units in ?7Li due to dyke-internal processes, such as fractionation, which increases ?7Li in late-stage lamproitic melts, and post-emplacement interaction with fluids that reduced ?7Li in samples that have lost Li. Post-emplacement alteration also led to the disturbance in the Pb isotope systematics of the differentiated orogenic lamproite as indicated by variable over-correction of in situ radiogenic Pb ingrowth.
DS202002-0198
2019
Krupnik, D., Khan, S.Close range, ground based hyperspectral imaging for mining applications at various scales: review and case studies. ( not specific to diamonds). Glossary addedEarth Science Reviews, Vol. 198, 34p. PdfGlobalhyperspectral

Abstract: Detailed mapping of mineral phases at centimeter scale can be useful for geological investigation, including resource exploration. This work reviews case histories of ground-based close-range hyperspectral imaging for mining applications. Studies of various economic deposits are discussed, as well as techniques used for data correction, integration with other datasets, and validation of spectral mapping results using geochemical techniques. Machine learning algorithms suggested for automation of the mining workflow are reviewed, as well as systems for environmental monitoring such as gas leak detection. Three new case studies that use a ground-based hyperspectral scanning system with sensors collecting data in the Visible Near-Infrared and Short-Wave Infrared portions of the electromagnetic spectrum in active and abandoned mines are presented. Vertical exposures in a Carlin Style sediment-hosted gold deposit, an active Cu-Au-Mo mine, and an active asphalt quarry are studied to produce images that delineate the extent of alteration minerals at centimeter scale to demonstrate an efficient method of outcrop characterization, which increases understanding of petrogenesis for mining applications. In the Carlin-style gold deposit, clay, iron oxide, carbonate, and jarosite minerals were mapped. In the copper porphyry deposit, different phases of alteration are delineated, some of which correspond to greater occurrence of ore deposits. A limestone quarry was also imaged, which contains bitumen deposits used for road paving aggregate. Review of current literature suggests use of this technology for automation of mining activities, thus reducing physical risk for workers in evaluating vertical mine faces.
DS202004-0524
2020
Kueter, N., Schmidt, M.W., Lilley, M.D., Bernasconi, S.Kinetic carbon isotope fractionation links graphite and diamond precipitation to reduced fluid sources.Earth and Planetary Science Letters, Vol. 529, 115848 12p. PdfGlobalcarbon

Abstract: At high temperatures, isotope partitioning is often assumed to proceed under equilibrium and trends in the carbon isotope composition within graphite and diamond are used to deduce the redox state of their fluid source. However, kinetic isotope fractionation modifies fluid- or melt-precipitated mineral compositions when growth rates exceed rates of diffusive mixing. As carbon self-diffusion in graphite and diamond is exceptionally slow, this fractionation should be preserved. We have hence performed time series experiments that precipitate graphitic carbon through progressive oxidization of an initially CH4-dominated fluid. Stearic acid was thermally decomposed at 800 °C and 2 kbar, yielding a reduced COH-fluid together with elemental carbon. Progressive hydrogen loss from the capsule caused CH4 to dissociate with time and elemental carbon to continuously precipitate. The newly formed C0, aggregating in globules, is constantly depleted by ‰ in 13C relative to the methane, which defines a temperature dependent kinetic graphite-methane 13C/12C fractionation factor. Equilibrium fractionation would instead yield graphite heavier than the methane. In dynamic environments, kinetic isotope fractionation may control the carbon isotope composition of graphite or diamond, and, extended to nitrogen, could explain the positive correlation of and sometimes observed in coherent diamond growth zones. 13C enrichment trends in diamonds are then consistent with reduced deep fluids oxidizing upon their rise into the subcontinental lithosphere, methane constituting the main source of carbon.
DS202004-0525
2019
Kumar, A., Fernandez, M., Jimenez-Munt, I., Torne, M., Verges, J., Afonso, J.C.LitMod2D_2.0: an improved integrated geophysical petrological modeling took for the physical interpretation of upper mantle anomalies.Geochemistry, Geophysics, Geosystems, 10.1029/2019GC008777. 19p.Mantlegeophysics

Abstract: LitMod2D integrates geophysical and petrological data sets to produce the thermal, density, and seismic velocity structure of the lithosphere and upper mantle. We present a new LitMod2D_2.0 package with improvements focused on (i) updated anelastic attenuation correction for anharmonic seismic velocities, (ii) chemical composition in the sublithospheric mantle, and (iii) incorporation of sublithospheric mantle anomalies. Sublithospheric mantle anomalies can be defined with different chemical composition, temperature, seismic velocities, and a combination of them, allowing the application of LitMod2D_2.0 to regions affected by mantle upwelling, subduction, delamination, and metasomatism. We demonstrate the potential application of LitMod2D_2.0 to such regions and the sensitivity of thermal and compositional anomalies on density and seismic velocities through synthetic models. Results show nonlinearity between the sign of thermal and seismic velocity anomalies, and that S wave velocities are more sensitive to temperature whereas P wave velocities are to composition. In a synthetic example of subduction, we show the sensitivity of sublithospheric mantle anomalies associated with the slab and the corner flow on surface observables (elevation, geoid height, and gravity anomalies). A new open?source graphic user interface is incorporated in the new package. The output of the code is simplified by writing only the relevant physical parameters (temperature, pressure, material type, density, and seismic velocities) to allow the user using predefined post?processing codes from a toolbox (flexure, mineral assemblages, synthetic passive seismological data, and tomography) or designing new ones. We demonstrate a post?processing example calculating synthetic seismic tomography, Rayleigh surface?wave dispersion curves, and P wave receiver functions from the output file of LitMod2D_2.0.
DS202009-1638
2020
Kumar, N., Sigh, A.P., Tiwari, V.M.Gravity anomalies, isostasy and density structure of the Indian continental lithosphere.Episodes, Vol. 43, 1, pp. 609-621.Indiageophysics, gravity

Abstract: Gravity anomalies across the Indian region depict most of the geological and tectonic domains of the Indian continental lithosphere, which evolved through Archean cratonic nucleation, Proterozoic accretion, Phanerozoic India-Eurasia plate convergence, and modification through many thermal perturbations and rifting. Integrated analysis of gravity and geoid anomalies together with topographic and heat flow data led to deciphering the mechanism of isostatic compensation of topographic and geological loads, lithospheric structure, and composition. This study discusses the nature of gravity (free-air, Bouguer and Isostatic) and geoid anomalies in relation to the topography, geology, and tectonics, and presents a lithospheric density model across the peninsular India and Himalaya. Southern peninsular Indian region shows relatively low Bouguer gravity anomalies compared to the northern region. The mobile belts are generally observed to have relatively higher Bouguer gravity anomalies, e.g., Eastern Ghats Mobile Belt compared to the shield regions. The gravity lows are observed over topographic features like the Western Ghats and Himalaya, while some of the topographic highs like Aravalli show positive gravity anomaly. The Indian Ocean Geoid Low varies from -82 m over Dharwar Craton to -98 m over the Southern Granulite Terrain and finally reaches a significant low of -106 m in the Indian Ocean. Flexural isostatic compensation with variable Effective Elastic Thickness (EET) ~10 km to 50 km prevails over the stable continental region. The lithospheric thickness varies from 80 km along the coastal region to 120-130 km beneath the Saurashtra Plateau, the Southern Granulite Terrain, and the Eastern Indian Shield, and reaches to more than 200 km under the Himalayan orogenic belt in the north. From Dharwar Craton to Bundelkhand Craton in central India, the lithospheric thickness varies between 160 and 180 km.
DS202008-1412
2020
Kumar, S., Gupta, S., Kanna, N., Sivaram, k.Crustal structures across the Deccan volcanic province and eastern Dharwar craton in south Indian shield using receiver function modelling.Physics of the Earth and Planetary Interiors, Vol. 306, 106543, 9p. PdfIndiageophysics -seismic

Abstract: The south Indian shield, primarily consisting of Archean cratons and Cretaceous-Tertiary Deccan Volcanic Province (DVP), has undergone several major tectonic episodes during its evolution. The Deccan volcanism at Cretaceous-Tertiary (~65 Ma) is the last major tectono-thermal event, which influenced a substantial part of the south Indian shield. To understand the influence of the Deccan volcanism on the evolution of the south Indian shield, we study the crustal seismic structure of the ~65 Ma Deccan Volcanic Province and the adjacent ~2.6 Ga Eastern Dharwar Craton (EDC), which forms the basement of the volcanic terrain. We calculate teleseismic receiver functions for 18 broadband seismic stations along a ~1000 km long seismological profile that cut across both the EDC and DVP. The analysis and modelling, using H-Vp/Vs stacking and generalized neighbourhood algorithm inversion of the receiver functions show distinct crustal structure (crustal thickness, average composition, shear wave velocity variation, nature of crust-mantle boundary, etc.) across the EDC and DVP. The results clearly indicate that the crustal structure is heterogeneous beneath the DVP compared to a relatively uniform structure below the EDC. Using results from this study along with earlier results, we infer that the present Eastern Dharwar Craton terrain is not affected by any tectono-thermal event for a long geological time, including the Deccan volcanism. Whereas, the present Deccan Volcanic Province is highly affected by the Reunion mantle plume-crust interaction.
DS202006-0930
2020
Kumar, S., Pal, S.K., Guha, A.Very low frequency electromagnetic ( VLF-EM) study over Wajrakakarur kimberlite pipe 6 in eastern Dharwar craton, India.Journal of Earth System Science, Vol. 129, 1, 102 10p. PdfIndiadeposit - Pipe 6

Abstract: The Wajrakarur kimberlite Pipe 6 in Eastern Dharwar Craton, is hardly explored using latest ground-based geophysical techniques. The present study uses the Very Low Frequency Electromagnetic (VLF-EM) method for understanding the aerial extension, depth and geometry of the kimberlite pipe. The VLF-EM data have been analyzed using Fraser filtering of in-phase component, 3D Euler deconvolution of Fraser filtered in-phase data, radially average power spectrum (RAPS) of VLF data (raw data) and 2D inversion of VLF data (raw data). The Fraser filtered in-phase grid anomaly map has witnessed as an effective tool for mapping extension of the kimberlite pipe. The maxima of Fraser filtered in-phase component has been observed as a key parameter to delineate the conducting bodies. The high apparent current density in Karous-Hjelt (K-H) pseudo section locate relatively conducting body possibly associated with kimberlite pipe. Two depth interfaces at about 15 and 32 m have been delineated using RAPS. 3D Euler solution indicate dyke-like structure associated with kimberlite pipe having depth solutions ranging from 6 to 40 m with mode of depth 17 m in the study area. 2D resistivity sections indicate that causative bodies are in the depth range of 15-50 m. The results of VLF-EM study are well validated using geological borehole data over the study area reported by Geological Survey of India.
DS202010-1853
2020
Kumar, S.P., Shaikh, A.M., Patel, S.C., Sheikh, J.M., Behera, D., Pruseth, K.L., Ravi, S.,Tappe, S.Multi-stage magmatic evidence of olivine-leucite lamproite dykes from Banganapalle, Dharwar craton, India: evidence from compositional zoning of spinel.Mineralogy and Petrology, doi.org/10.1007/s00710-020-00722-y 26p. PdfIndialamproite

Abstract: Mesoproterozoic lamproite dykes occurring in the Banganapalle Lamproite Field of southern India show extensive hydrothermal alteration, but preserve fresh spinel, apatite and rutile in the groundmass. Spinels belong to three genetic populations. Spinels of the first population, which form crystal cores with overgrowth rims of later spinels, are Al-rich chromites derived from disaggregated mantle peridotite. Spinels of the second population include spongy-textured grains and alteration rims of titanian magnesian aluminous chromites that formed by metasomatic interactions between mantle wall-rocks and precursor lamproite melts before their entrainment into the erupting lamproite magma. Spinels that crystallised directly from the lamproite magma constitute the third population and show five distinct compositional subtypes (spinel-IIIa to IIIe), which represent discrete stages of crystal growth. First stage magmatic spinel (spinel-IIIa) includes continuously zoned macrocrysts of magnesian aluminous chromite, which formed together with Al-Cr-rich phlogopite macrocrysts from an earlier pulse of lamproite magma at mantle depth. Crystallisation of spinel during the other four identified stages occurred during magma emplacement at crustal levels. Titanian magnesian chromites (spinel-IIIb) form either discrete crystals or overgrowth rims on spinel-IIIa cores. Further generations of overgrowth rims comprise titanian magnesian aluminous chromite (spinel-IIIc), magnetite with ulvöspinel component (spinel-IIId) and lastly pure magnetite (spinel-IIIe). Abrupt changes of the compositions between successive zones of magmatic spinel indicate either a hiatus in the crystallisation history or co-crystallisation of other groundmass phases, or possibly magma mixing. This study highlights how different textural and compositional populations of spinel provide important insights into the complex evolution of lamproite magmas including clues to elusive precursor metasomatic events that affect cratonic mantle lithosphere.
DS202001-0025
2019
Kumari, S., Debajyoti, P., Stracke, A.Constraints on Archean crust formation from open system models of Earth evolution.Chemical Geology, doi.org/10.1016/ j.chemgeo.2019. 119307Mantlecraton

Abstract: Establishing the mode and rate of formation of the continental crust is crucial for quantifying mass exchange between Earth’s crust and mantle. The limited crustal rock record, particularly of early Archean rocks, has led to a variety of different models of continental growth. Here, we present an open-system model of silicate Earth evolution incorporating the Sm-Nd and Lu-Hf isotope systematics with the aim to constrain crustal growth during the Archean and its effect on the chemical and isotopic evolution of Earth’s crust-mantle system. Our model comprises four reservoirs: the bulk continental crust (CC), depleted upper mantle (UM), lower mantle (LM), and an isolated reservoir (IR) where recycled crust is stored transiently before being mixed with the LM. The changing abundance of isotope species in each reservoir is quantified using a series of first order linear differential equations that are solved numerically using the fourth order Runge-Kutta method at 1 Myr time steps for 4.56 Gyr (the age of the Earth). The model results show that only continuous and exponential crustal growth reproduces the present-day abundances and isotope ratios in the terrestrial reservoirs. Our preferred crustal growth model suggests that the mass of the CC by the end of Hadean (4.0 Ga) and end of Archean (2.5 Ga) was ?30% and ?75% of the present-day mass of the CC, respectively. Models proposing formation of most (?90%) of the present-day CC during the initial 1 Gyr or nearly 50-60% during the last 1 Gyr are least favorable. Significant mass exchange between crust and mantle, that is, both the formation and recycling of crust, started in the Hadean with Sm-Nd and Lu-Hf isotope evolution typical for mafic rocks. Depletion of the UM (in incompatible elements) during the early Archean is mitigated by the input of recycled crust, so that the UM maintained a near-primitive Hf-Nd isotope composition. The LM also retained a near-primitive Hf-Nd isotope composition during the Archean, but for different reasons. In contrast to the UM, the crustal return flux into the LM is transiently stored (? 1 Gyr) in an isolated reservoir (IR), which limits the mass flux into and out of the LM. The IR in our model is distinct from other mantle reservoirs and possibly related to stable crustal blocks or, alternatively, to recycled crust in the mantle that remains temporarily isolated, perhaps at the core-mantle boundary (LLSVPs).
DS202010-1854
2016
Kurszlaukis, S., Lorenz, V.Difference and similarities between emplacement models of kimberlite and basaltic maar-diatreme volcanoes.IN: Nemeth, K., Carrasco-Nunez, G., Aranda-Gomez, J.J., Smith, I.E.M. eds. Monogenetic volcanism GSL Special Volume, Vol. 446, 22p. Pdf * note dateEuropekimberlite, maars

Abstract: Most kimberlite maar-diatreme volcanoes erupted during the Tertiary or earlier and therefore their tephra rings and, less often, their near-surface diatreme-filling deposits have usually been eliminated by erosion. Poorly eroded Quaternary non-kimberlite maar-diatreme volcanoes, especially those of mafic and ultramafic magma types, have the same diatreme size range (diameter and depth) as kimberlite pipes and show similar internal volcaniclastic diatreme lithofacies. In addition, these young volcanoes often have a more or less preserved tephra ring consisting of hundreds to perhaps a few thousand thin tephra beds. Volcanological analyses of the xenolith-rich primary volcaniclastic deposits both within these diatremes and in the tephra ring beds reflect phases of explosive pipe growth and are of convincingly phreatomagmatic origin. The similarities between non-kimberlite pipes and kimberlite pipes suggest to some researchers that phreatomagmatic processes were also responsible for pipe excavation processes in kimberlite maar-diatreme volcanoes. In contrast, other researchers have suggested that kimberlite maar-diatreme volcanoes were emplaced largely by magmatic processes as a consequence of exsolution and the explosive expansion of juvenile volatiles. We therefore analysed and compared some key geological features of kimberlite and ultrabasic to basic ‘basaltic’ maar-diatreme volcanoes to determine similarities and differences with respect to their emplacement behaviour. The following problems were addressed - the layout of the abstract; an amendment to the caption of Fig. 1; and some changes to Zimanowski's references in the reference list.
DS202005-0744
2020
Labidi, J., Barry, P.H., Bekaert, D.V., Broadley, M.W., Marty, B., Giunta, T., Warr, O., Sherwood Lollar, B., Fischer, T.P., Avice, G., Caracusi, A., Ballentine, C.J., Halldorsson, S.A., Stefansson, A., Kurz, M.D., Kohl, I.E., Young, E.D.Hydrothermal 15N15N abundances constrain the origins of mantle nitrogen.Nature, Vol. 580, 7803 pp. 367-371. Mantlenitrogen

Abstract: Nitrogen is the main constituent of the Earth’s atmosphere, but its provenance in the Earth’s mantle remains uncertain. The relative contribution of primordial nitrogen inherited during the Earth’s accretion versus that subducted from the Earth’s surface is unclear1,2,3,4,5,6. Here we show that the mantle may have retained remnants of such primordial nitrogen. We use the rare 15N15N isotopologue of N2 as a new tracer of air contamination in volcanic gas effusions. By constraining air contamination in gases from Iceland, Eifel (Germany) and Yellowstone (USA), we derive estimates of mantle ?15N (the fractional difference in 15N/14N from air), N2/36Ar and N2/3He. Our results show that negative ?15N values observed in gases, previously regarded as indicating a mantle origin for nitrogen7,8,9,10, in fact represent dominantly air-derived N2 that experienced 15N/14N fractionation in hydrothermal systems. Using two-component mixing models to correct for this effect, the 15N15N data allow extrapolations that characterize mantle endmember ?15N, N2/36Ar and N2/3He values. We show that the Eifel region has slightly increased ?15N and N2/36Ar values relative to estimates for the convective mantle provided by mid-ocean-ridge basalts11, consistent with subducted nitrogen being added to the mantle source. In contrast, we find that whereas the Yellowstone plume has ?15N values substantially greater than that of the convective mantle, resembling surface components12,13,14,15, its N2/36Ar and N2/3He ratios are indistinguishable from those of the convective mantle. This observation raises the possibility that the plume hosts a primordial component. We provide a test of the subduction hypothesis with a two-box model, describing the evolution of mantle and surface nitrogen through geological time. We show that the effect of subduction on the deep nitrogen cycle may be less important than has been suggested by previous investigations. We propose instead that high mid-ocean-ridge basalt and plume ?15N values may both be dominantly primordial features.
DS202002-0199
2020
Lai, M.Y., Breeding, C.M., Stachel, T., Stern, R.A.Spectroscopic features of natural and HPHT treated yellow diamonds. EkatiDiamonds & Related Materials, Vol. 101, 107642, 8p. PdfCanada, Northwest Territoriesdeposit - Ekati

Abstract: High pressure high temperature (HPHT) treatment has long been applied in the gem trade for changing the body colour of diamonds. The identification of HPHT-treated diamonds is a field of on-going research in gemological laboratories, as different parameters of treatment will result in either the creation or the destruction of a variety of lattice defects in diamonds. Some features that exist in treated diamonds can also be found in natural diamonds, and consequently must not be employed for the separation of treated and natural diamonds. In this research, we investigated the properties of 11 natural yellow diamonds (directly obtained from the Ekati Diamond Mine to ensure that they are untreated) before and after HPHT treatment, conducted at a temperature of 2100 °C and a pressure of 6 GPa for 10 min. We report spectroscopic data and fluorescence characteristics, collected using PL mapping, FTIR mapping and fluorescence imaging showing the distribution of lattice defects and internal growth structures. PL mapping indicates SiV defects exist in one of the nitrogen-rich natural diamonds prior to treatment. Silicon-related defects can also be created by HPHT treatment, and they seem to show a relationship with pre-existing NV? centres. SIMS analysis was conducted to confirm the presence of silicon in these diamonds. The increase in the hydrogen-related infrared absorption peak at 3107 cm?1 (VN3H) is very strong in some diamonds that do not form B-centres during treatment. NVH was observed in our HPHT-treated natural diamonds, so it is possible that this strong increase in VN3H suppresses the aggregation of A- to B-centres as the newly formed A-centres were captured by NVH lattice defects to form VN3H. HPHT-altered and HPHT-induced platelet peaks are different from their natural counterparts in peak width and shape. Strong green fluorescence over a large area of a diamond, which is linked to relatively high concentration of H3 centres, was produced after HPHT treatment. We are confident that the unusual platelet peaks and strong emission of H3 centres are reliable indicators for HPHT-treated diamonds as they are not observed in untreated natural diamonds.
DS202003-0347
2020
Lai, M.Y., Stachel, T., Breeding, C.M., Stern, R.A.Yellow diamonds with colourless cores - evidence for episodic diamond growth beneath Chidliak and Ekati mine, Canada.Mineralogy and Petrology, in press available 13p. PdfCanada, Northwest Territoriesdeposit - Chidliak, Ekati

Abstract: Yellow diamonds from the CH-7 (Chidliak) and the Misery (Ekati Mine) kimberlites in northern Canada are characterised for their nitrogen characteristics, visible light absorption, internal growth textures, and carbon isotope compositions. The diamonds are generally nitrogen-rich, with median N contents of 1230 (CH-7) and 1030 at.ppm (Misery). Normally a rare feature in natural diamonds, single substitutional nitrogen (C centres) and related features are detected in infrared absorption spectra of 64% of the studied diamonds from CH-7 and 87% from Misery and are considered as the major factor responsible for their yellow colouration. Episodically grown diamonds, characterised by colourless cores containing some nitrogen in the fully aggregated form (B centres) and yellow outer layers containing C centres, occur at both localities. Carbon isotope compositions and N contents also are significantly different in such core and rim zones, documenting growth during at least two temporally distinct events and involving different diamond forming fluids. Based on their nitrogen characteristics, both the yellow diamonds and yellow rims must have crystallized in close temporal proximity (<<1 Ma) to kimberlite activity at CH-7 and Misery.
DS202002-0200
2019
Lai, X., Yang, X.U-Pb ages and Hf isotope of zircons from a carbonatite dyke in the Bayan Obo Fe-REE deposit in Inner Mongolia: its geological significance.Acta Geologica Sinica, Vol. 93, 6, pp. 1783-1796.China, MongoliaREE

Abstract: Detailed studies on U?Pb ages and Hf isotope have been carried out in zircons from a carbonatite dyke associated with the Bayan Obo giant REE?Nb?Fe deposit, northern margin of the North China Craton (NCC), which provide insights into the plate tectonic in Paleoproterozoic. Analyses of small amounts of zircons extracted from a large sample of the Wu carbonatite dyke have yielded two ages of late Archaean and late Paleoproterozoic (with mean 207Pb/206Pb ages of 2521±25 Ma and 1921±14 Ma, respectively). Mineral inclusions in the zircon identified by Raman spectroscopy are all silicate minerals, and none of the zircon grains has the extremely high Th/U characteristic of carbonatite, which are consistent with crystallization of the zircon from silicate, and the zircon is suggested to be derived from trapped basement complex. Hf isotopes in the zircon from the studied carbonatite are different from grain to grain, suggesting the zircons were not all formed in one single process. Majority of ?Hf(t) values are compatible with ancient crustal sources with limited juvenile component. The Hf data and their TDM2 values also suggest a juvenile continental growth in Paleoproterozoic during the period of 1940-1957 Ma. Our data demonstrate the major crustal growth during the Paleoproterozoic in the northern margin of the NCC, coeval with the assembly of the supercontinent Columbia, and provide insights into the plate tectonic of the NCC in Paleoproterozoic.
DS202010-1855
2019
Lange, V.T., Lorenz, V., Koppen, K-H, Buchel, G.New aspects of the volcanism of the West Eifel. *** GERJber. Mitt. oberrhein. Geol. Ver. N.F. English abstract, Vol. 101, pp. 227-250. 24p. PdfEurope, Germany guidebook
DS202002-0201
2019
Larson, K.M.Unanticipated uses of the Global Positioning System.Annual Review of Earth and Planetary Sciences, Vol. 47, pp. 19-40.GlobalGPS system

Abstract: Global Positioning System (GPS) instruments are routinely used today to measure crustal deformation signals from tectonic plate motions, faulting, and glacial isostatic adjustment. In parallel with the expansion of GPS networks around the world, several new and unexpected applications of GPS have been developed. For example, GPS instruments are now being used routinely to measure ground motions during large earthquakes. Access to real-time GPS data streams has led to the development of better hazard warnings for tsunamis, flash floods, earthquakes, and volcanic eruptions. Terrestrial water storage changes can be derived from GPS vertical coordinate time series. Finally, GPS signals that reflect on the surfaces below a GPS antenna can be used to measure soil moisture, snow accumulation, vegetation water content, and water levels. In the future, combining GPS with the signals from the Russian, European, and Chinese navigation constellations will significantly enhance these applications.
DS202005-0745
2019
Larson, K.M.Unanticipated uses of the Global Positioning System. Just interesting not specific to diamonds.Annual Review of Earth and Planetary Sciences, Vol. 47, pp. 19-40. pdfGlobalGPS

Abstract: Global Positioning System (GPS) instruments are routinely used today to measure crustal deformation signals from tectonic plate motions, faulting, and glacial isostatic adjustment. In parallel with the expansion of GPS networks around the world, several new and unexpected applications of GPS have been developed. For example, GPS instruments are now being used routinely to measure ground motions during large earthquakes. Access to real-time GPS data streams has led to the development of better hazard warnings for tsunamis, flash floods, earthquakes, and volcanic eruptions. Terrestrial water storage changes can be derived from GPS vertical coordinate time series. Finally, GPS signals that reflect on the surfaces below a GPS antenna can be used to measure soil moisture, snow accumulation, vegetation water content, and water levels. In the future, combining GPS with the signals from the Russian, European, and Chinese navigation constellations will significantly enhance these applications. 1) GPS data are now routinely used to study the dynamics of earthquake rupture. 2) GPS instruments are an integral part of warning systems for earth- quakes, tsunamis, flash floods, and volcanic eruptions. 3) Reflected GPS signals provide a new source of soil moisture, snow depth, vegetation water content, and tide gauge data. 4)GPS networks can sense changes in soil moisture, groundwater, and snow depth and thus can contribute to water resource assessments.
DS202004-0526
2020
Laturtrie. B., Ross, P-S.Phreatomagmatic vs magmatic eruptive styles in maar-diatremes: a case study at Twin Peaks, Hopi Buttes volcanic field, Navajo Nation, Arizona.Bulletin of Volcanology, Vol. 82, 28.United States, Arizonamagmatism

Abstract: The Hopi Buttes volcanic field (HBVF) is located on the Colorado Plateau, Northern Arizona. In this Miocene volcanic field, the erosion level increases southward, allowing the study of maar-diatreme volcanoes from top (posteruptive crater infill and ejecta ring) to bottom (lower diatreme). The Twin Peaks volcanic complex consists mostly of two hills (North Peak and South Peak) with thick lavas at their summits and pyroclastic rocks underneath. In the HBVF, such volcanic remnants have received little scientific attention so far, despite their relative abundance. Our field observations allow us to interpret the North and South Peaks as remnants of two maar-diatreme volcanoes which evolved into lava lakes filling the craters. Within the complex, we distinguish four volcanic units (from unit 1 at the bottom to unit 4 at the top). On the basis of the field description of the deposits and the componentry measurements, we suggest that unit 1 is phreatomagmatic, unit 2 is phreato-strombolian (with mixed phreatomagmatic and strombolian characteristics), unit 3a is phreato-hawaiian (with mixed phreatomagmatic and hawaiian characteristics), unit 3b is hawaiian (formed by lava fountains) and unit 4 consists of lava lakes filling the maar craters. There is therefore a progressive evolution from a purely phreatomagmatic eruptive style, which excavated the craters and diatremes and partly filled them, to magmatic explosive to nonexplosive eruptive styles, which filled the maar craters up to the pre-eruptive surface. We discuss traditional criteria used to distinguish phreatomagmatic from magmatic eruptive styles in ultramafic to mafic maar-diatreme volcanoes.
DS202011-2049
2020
Lau, H., Holtzman, B., Havlin, C.Towards a self-consistent characterization of lithospheric plates using full-spectrum viscoelasticity.AGU Advances, dor.or/10.101029 /2020AV000205Mantletectonics

Abstract: On Earth, broken, rigid tectonic plates lie atop slowly flowing mantle rock (over millions to billions of years). A basic understanding of the global variation in thickness of this rigid lid provides the foundation to many geodynamical predictions. However, using different techniques to estimate its thickness, for example, seismic wave propagation (acting on timescales of seconds), to the warping of plates under the weight of volcanoes (acting on timescales of millions of years) reveals many inconsistencies. At the heart of these inconsistencies is the fact that rock deforms differently to forces acting on different timescales. At very fast timescales rock deforms like an elastic solid, but at much longer timescales, rock flows. To resolve these inconsistencies, we attempt to coherently tie these disparate observations together to reach a more holistic understanding of plate thickness, accounting for these timescale effects. By incorporating current understanding on rock deformation from laboratory experiments, we demonstrate that on fast timescales (of the seismic waves used to image the Earth's interior), tectonic plates appear significantly thicker than the true thickness at million? to billion?year timescales of plate tectonics. This demonstration involves a new theoretical and conceptual framework for interpreting distinct observations acting on vastly different timescales.
DS202002-0202
2020
Lawley, C.J.M., Pearson, G., Waterton, P., Zagorevski, A., Bedard, J.H., Jackson, S.E., Petts, D.C., Kjarsgaard, B.A., Zhang, S., Wright, D.Element and isotopic signature of re-fertilized mantle peridotite as determined by nanopower and olivine LA-ICPMS analyses.Chemical Geology, DOI:101016/ j.chemgeo.2020.119464Mantleperidotite

Abstract: The lithospheric mantle should be depleted in base- and precious-metals as these elements are transferred to the crust during partial melting. However, some melt-depleted mantle peridotites are enriched in these ore-forming elements. This may reflect re-fertilization of the mantle lithosphere and/or sequestering of these elements by residual mantle phase(s). Both processes remain poorly understood because of the low abundances of incompatible elements in peridotite and the nugget-like distribution of digestion-resistant mantle phases that pose analytical challenges for conventional geochemical methods. Herein we report new major and trace element concentrations for a suite of mantle peridotite and pyroxenite samples from the Late Permian to Middle Triassic Nahlin ophiolite (Cache Creek terrane, British Columbia, Canada) using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) analysis of nanoparticulate powders and olivine. Compatible to moderately incompatible element concentrations suggest that Nahlin ophiolite peridotites represent residues after ?20% melt extraction. Pyroxenite dykes and replacive dunite bands are folded and closely intercalated with residual harzburgite. These field relationships, coupled with the presence of intergranular base metal sulphide, clinopyroxene and Cr-spinel at the microscale, point to percolating melts that variably re-fertilized melt-depleted mantle peridotite. Radiogenic Pb (206Pb/204Pb?=?15.402-19.050; 207Pb/204Pb?=?15.127-15.633; 208Pb/204Pb?=?34.980-38.434; n?=?45) and Os (187Os/188Os 0.1143-0.5745; n?=?58) isotope compositions for a subset of melt-depleted peridotite samples further support metasomatic re-fertilization of these elements. Other ore-forming elements are also implicated in these metasomatic reactions because some melt-depleted peridotite samples are enriched relative to the primitive mantle, opposite to their expected behaviour during partial melting. New LA-ICPMS analysis of fresh olivine further demonstrates that a significant proportion of the highly incompatible element budget for the most melt-depleted rocks is either hosted by, and/or occurs as trapped inclusions within, the olivine-rich residues. Trapped phases from past melting and/or re-fertilization events are the preferred explanation for unradiogenic Pb isotope compositions and Paleozoic to Paleoproterozoic Re-depletion model ages, which predate the Nahlin ophiolite by over one billion years.
DS202008-1413
2020
Le Roex, A., Tinguely, C., Gregoire, M.Eclogite and garnet pyroxenite xenoliths from kimberlites emplaced along the southern margin of the Kaapvaal craton, southern Africa: mantle or lower crustal fragments?Journal of Petrology, https://doi.org/ 10.1093/petrology /egaa040 50p. PdfAfrica, South Africakimberlites

Abstract: Eclogite xenoliths, together with garnet pyroxenites and some mafic garnet granulites, found in kimberlites located along the southern margin of the Kaapvaal craton in southern Africa have been analysed by electron microprobe and mass spectrometry techniques to determine their geochemical characteristics. The majority of eclogites are bimineralic with garnet and omphacitic clinopyroxene in subequal proportions, with rutile as the main accessory phase; a few contain kyanite. Based on K2O in clinopyroxene and Na2O in garnet, the eclogites can be classified as Group II eclogites, and the majority are high-Ca in character. Garnet pyroxenites comprise garnet clinopyroxenites and garnet websterites. Major and trace element concentrations and isotope ratios of reconstituted bulk rock compositions of the eclogites and garnet pyroxenites allow constraints to be placed on depth of origin and likely protolith history. Calculated Fe–Mg exchange equilibration temperatures for the eclogites range from 815 to 1000?°C, at pressures of 1·7?±?0·4?GPa as determined by REE partitioning, indicating that they were sampled from depths of 50–55?km; i.e. within the lower crust of the Namaqua–Natal Belt. The garnet pyroxenites show slightly lower temperatures (686–835?°C) at similar pressures of equilibration. Initial 143Nd/144Nd and 87Sr/86Sr ratios (calculated to time of kimberlite emplacement) of both lithologies overlap the field for lower crustal samples from the Namaqua–Natal Belt. Further evidence for a crustal origin is found in the similar REE patterns shown by many of the associated garnet granulite xenoliths. Garnet pyroxenites are interpreted to have a similar origin as the associated eclogites but with the mafic protolith having insufficient Na (i.e. low modal plagioclase) to allow for development of omphacitic pyroxene. Metamorphism of the mafic protoliths to these eclogites and garnet pyroxenites is inferred to have occurred during crustal shortening and thickening associated with the collision of the Namaqua–Natal Belt with the Kaapvaal craton at 1–1·2?Ga.
DS202009-1639
2020
Le Roex, A., Tinguely, C., Gregoire, M.Eclogite and garnet pyroxenite xenoliths from kimberlites emplaced along the southern margin of the Kaapvaal Craton, southern Africa: mantle or lower crustal fragments?Journal of Petrology, pp. 1-32. pdf.Africa, South Africaeclogite, pyroxenite

Abstract: Eclogite xenoliths, together with garnet pyroxenites and some mafic garnet granulites, found in kimberlites located along the southern margin of the Kaapvaal craton in southern Africa have been analysed by electron microprobe and mass spectrometry techniques to determine their geochemical characteristics. The majority of eclogites are bimineralic with garnet and omphacitic clinopyroxene in subequal proportions, with rutile as the main accessory phase; a few contain kyanite. Based on K2O in clinopyroxene and Na2O in garnet, the eclogites can be classified as Group II eclogites, and the majority are high-Ca in character. Garnet pyroxenites comprise garnet clinopyroxenites and garnet websterites. Major and trace element concentrations and isotope ratios of reconstituted bulk rock compositions of the eclogites and garnet pyroxenites allow constraints to be placed on depth of origin and likely protolith history. Calculated Fe-Mg exchange equilibration temperatures for the eclogites range from 815 to 1000?°C, at pressures of 1•7?±?0•4?GPa as determined by REE partitioning, indicating that they were sampled from depths of 50-55?km; i.e. within the lower crust of the Namaqua-Natal Belt. The garnet pyroxenites show slightly lower temperatures (686-835?°C) at similar pressures of equilibration. Initial 143Nd/144Nd and 87Sr/86Sr ratios (calculated to time of kimberlite emplacement) of both lithologies overlap the field for lower crustal samples from the Namaqua-Natal Belt. Further evidence for a crustal origin is found in the similar REE patterns shown by many of the associated garnet granulite xenoliths. Garnet pyroxenites are interpreted to have a similar origin as the associated eclogites but with the mafic protolith having insufficient Na (i.e. low modal plagioclase) to allow for development of omphacitic pyroxene. Metamorphism of the mafic protoliths to these eclogites and garnet pyroxenites is inferred to have occurred during crustal shortening and thickening associated with the collision of the Namaqua-Natal Belt with the Kaapvaal craton at 1-1•2?Ga.
DS202008-1414
2020
Lebedeva, N., Nosova, A., Kargin, A., Larionova, Y., Sazonova, L., Tikhomirova, Y.Grib kimberlite peridotitic xenoliths: isotopic evidence of variable source of mantle metasomatism.Goldschmidt 2020, 1p. AbstractRussia, Kola Peninsuladeposit - Grib

Abstract: We present petrography and mineral chemistry for both phlogopite, from mantle-derived xenoliths (garnet peridotite, eclogite and clinopyroxene-phlogopite rocks) and for megacryst, macrocryst and groundmass flakes from the Grib kimberlite in the Arkhangelsk diamond province of Russia to provide new insights into multi-stage metasomatism in the subcratonic lithospheric mantle (SCLM) and the origin of phlogopite in kimberlite. Based on the analysed xenoliths, phlogopite is characterized by several generations. The first generation (Phl1) occurs as coarse, discrete grains within garnet peridotite and eclogite xenoliths and as a rock-forming mineral within clinopyroxene-phlogopite xenoliths. The second phlogopite generation (Phl2) occurs as rims and outer zones that surround the Phl1 grains and as fine flakes within kimberlite-related veinlets filled with carbonate, serpentine, chlorite and spinel. In garnet peridotite xenoliths, phlogopite occurs as overgrowths surrounding garnet porphyroblasts, within which phlogopite is associated with Cr-spinel and minor carbonate. In eclogite xenoliths, phlogopite occasionally associates with carbonate bearing veinlet networks. Phlogopite, from the kimberlite, occurs as megacrysts, macrocrysts, microcrysts and fine flakes in the groundmass and matrix of kimberlitic pyroclasts. Most phlogopite grains within the kimberlite are characterised by signs of deformation and form partly fragmented grains, which indicates that they are the disintegrated fragments of previously larger grains. Phl1, within the garnet peridotite and clinopyroxene-phlogopite xenoliths, is characterised by low Ti and Cr contents (TiO2 < 1 wt.%, Cr2O3 < 1 wt.% and Mg# = 100 × Mg/(Mg + Fe) > 92) typical of primary peridotite phlogopite in mantle peridotite xenoliths from global kimberlite occurrences. They formed during SCLM metasomatism that led to a transformation from garnet peridotite to clinopyroxene-phlogopite rocks and the crystallisation of phlogopite and high-Cr clinopyroxene megacrysts before the generation of host-kimberlite magmas. One of the possible processes to generate low-Ti-Cr phlogopite is via the replacement of garnet during its interaction with a metasomatic agent enriched in K and H2O. Rb-Sr isotopic data indicates that the metasomatic agent had a contribution of more radiogenic source than the host-kimberlite magma. Compared with peridotite xenoliths, eclogite xenoliths feature low-Ti phlogopites that are depleted in Cr2O3 despite a wider range of TiO2 concentrations. The presence of phlogopite in eclogite xenoliths indicates that metasomatic processes affected peridotite as well as eclogite within the SCLM beneath the Grib kimberlite. Phl2 has high Ti and Cr concentrations (TiO2 > 2 wt.%, Cr2O3 > 1 wt.% and Mg# = 100 × Mg/(Mg + Fe) < 92) and compositionally overlaps with phlogopite from polymict breccia xenoliths that occur in global kimberlite formations. These phlogopites are the product of kimberlitic magma and mantle rock interaction at mantle depths where Phl2 overgrew Phl1 grains or crystallized directly from stalled batches of kimberlitic magmas. Megacrysts, most macrocrysts and microcrysts are disintegrated phlogopite fragments from metasomatised peridotite and eclogite xenoliths. Fine phlogopite flakes within kimberlite groundmass represent mixing of high-Ti-Cr phlogopite antecrysts and high-Ti and low-Cr kimberlitic phlogopite with high Al and Ba contents that may have formed individual grains or overgrown antecrysts. Based on the results of this study, we propose a schematic model of SCLM metasomatism involving phlogopite crystallization, megacryst formation, and genesis of kimberlite magmas as recorded by the Grib pipe.
DS202005-0746
2020
Lebedeva, N., Nosova, A.A., Kargin, A., Sazonova, L.V.Multi-stage evolution of kimberlite melt as inferred from inclusions in garnet megacrysts in the Grib kimberlite ( Arkangelsk region, Russia.Mineralogy and Petrology, doi: 10.1007/s00710- 020-00704-0 in press 16p. PdfRussia, Arkangeldeposit - Grib

Abstract: To provide new insights into the origin of garnet megacrysts and evolution of kimberlite melts, we studied in detail the polymineralic and monomineralic inclusions and their host garnets from the Grib kimberlite (Arkhangelsk diamond province, Russia). Low-Cr and high-Cr garnet megacrysts and eclogitic garnets contain abundant polymineralic and rare monomineralic inclusions. Monomineralic inclusions presented by clinopyroxene, ilmenite, olivine replaced by serpentine, were found exclusively within the low-Cr megacrysts. The composition of clinopyroxene exhibits geochemical equilibrium with the host garnet, indicating its primary origin during the formation of the megacryst assemblage. The low-Cr garnet-clinopyroxene mineral assemblage formed as a result of high-temperature, melt-associated mantle metasomatism by failed kimberlite within the lithospheric mantle (T = 1150 °C and P = 5.5 GPa). Polymineralic inclusions are characterised by a silicate or silicate-sulphate matrix. The central part of the silicate inclusions is filled by serpentine and contains ilmenite, spinel, perovskite, calcite and apatite. At the contact with host garnets, phlogopite, spinel and amphibole occur as reaction minerals. Composition of spinel and other minerals within inclusions with silicate matrix suggests that kimberlite melt was trapped at mantle pressures. Inclusions with silicate matrix were found in all garnets. The matrix of silicate-sulphate inclusions consists of silicate cryptocrystalline phases and sulphate minerals (celestine-barite) and contains calcite grains. The inclusions are distributed in some low-Cr garnet megacrysts and eclogitic garnet. The silicate-sulphate inclusions were crystallised from the late-stage kimberlite melt. Diverse reaction textures are evidences of disequilibrium between the host crystals and polymineralic inclusions and indicate that garnet and the hosted inclusions reacted with the ascending kimberlite melt. The silicate-sulphate inclusions with a thin rim of epidote within eclogitic garnets indicate that a kimberlite melt invaded the garnet and induced partial melting. The studied inclusions allow us to propose three stages of the Grib kimberlite evolution: 1) generation of garnet megacrysts and primary inclusions due to melt metasomatism, 2) reaction of the high-Ti kimberlite melt with garnet megacrysts (including their dissolution) and 3) alteration of the inclusions in garnet after kimberlite ascent.
DS202010-1856
2020
Lebedeva, N.M., Nosova, A.A., Kargin, A.V., Larionova, Y.O., Sazonova, L.V., Tikhomirova, Y.S.S-Nd-O isotopic evidence of variable sources of mantle metasomatism in the subcratonic lithospheric mantle beneath the Grib kimberlite, northwestern Russia.Lithos, in press available, 54p. PdfRussia, Kola Peninsuladeposit - Grib

Abstract: To provide new insights into the type and extent of mantle metasomatism in the subcratonic lithospheric mantle, we examined the Sr-Nd-O isotopic compositions of orthopyroxene, clinopyroxene, garnet, ilmenite and phlogopite from sheared garnet lherzolite, granular garnet harzburgites and lherzolites and clinopyroxene-phlogopite rocks from the Grib kimberlite in the Arkhangelsk diamond province in northwestern Russia. Clinopyroxene and orthopyroxene from sheared garnet lherzolite initially have a close value of 87Sr/86Sr(t) (~0.7034) and close weak positive ?Nd. Orthopyroxene and clinopyroxene are in oxygen isotope equilibrium with coexisting olivine. Clinopyroxene from a garnet harzburgite has a low 87Sr/86Sr(t) isotope ratio of 0.70266. Clinopyroxene from granular garnet lherzolites has a relatively narrow variation in 87Sr/86Sr(t) (0.70456-0.70582) and considerably larger variations in ?Nd (?4.3???+1.0) isotope ratios. Garnet displays elevated initial 87Sr/86Sr(t) values (0.70540-0.70633). Ilmenite shows a narrow range in 87Sr/86Sr(t) (0.70497-0.70522) coupled with ?Nd values of +0.4 and +3.5. These isotopic data suggest granular garnet lherzolite of mantle metasomatism took place during the interaction of kimberlite melts with SCLM that contained mica-amphibole-rutile-ilmenite-diopside (MARID)-type metasomes. Clinopyroxenes from clinopyroxene-phlogopite (phlogopite wehrlite) xenoliths display a broader range in 87Sr/86Sr(t) (0.70486-0.70813) that is significantly higher than the kimberlite values and a circa-chondritic ?Nd (?0.1 ??+1.3) with a restricted ?18O range (5.11‰-5.33‰). More radiogenic Sr isotopic composition decoupled from Nd isotopes could have been induced by metasomatic melt/fluid related to a subducted material. The isotopic compositions of mantle minerals preserve Sr-Nd isotopic evidence of pre-kimberlite metasomatic events that were probably due to incomplete reequilibration with ultramafic carbonated melt. Based on mineral pairs Rb-Sr isochrons and a clinopyroxene-based Sm-Nd errochron, these mantle metasomatic events correspond to ~550-600?Ma and ~1200?Ma episodes of magmatic-thermal activity.
DS202008-1415
2020
Lebedeva, N.M., Nosova, A.A., Kargin, A.V., Sazonova, L.V.Multi-stage evolution of kimberlite melt as inferred from inclusions in garnet megacrysts in the Grib kimberlite ( Arkangelsk region, Russia).Mineralogy and Petrology, Vol. 114, 4, pp. 272-288. pdfRussia, Archangeldeposit - Grib

Abstract: To provide new insights into the origin of garnet megacrysts and evolution of kimberlite melts, we studied in detail the polymineralic and monomineralic inclusions and their host garnets from the Grib kimberlite (Arkhangelsk diamond province, Russia). Low-Cr and high-Cr garnet megacrysts and eclogitic garnets contain abundant polymineralic and rare monomineralic inclusions. Monomineralic inclusions presented by clinopyroxene, ilmenite, olivine replaced by serpentine, were found exclusively within the low-Cr megacrysts. The composition of clinopyroxene exhibits geochemical equilibrium with the host garnet, indicating its primary origin during the formation of the megacryst assemblage. The low-Cr garnet–clinopyroxene mineral assemblage formed as a result of high-temperature, melt-associated mantle metasomatism by failed kimberlite within the lithospheric mantle (T?=?1150 °C and P?=?5.5 GPa). Polymineralic inclusions are characterised by a silicate or silicate-sulphate matrix. The central part of the silicate inclusions is filled by serpentine and contains ilmenite, spinel, perovskite, calcite and apatite. At the contact with host garnets, phlogopite, spinel and amphibole occur as reaction minerals. Composition of spinel and other minerals within inclusions with silicate matrix suggests that kimberlite melt was trapped at mantle pressures. Inclusions with silicate matrix were found in all garnets. The matrix of silicate-sulphate inclusions consists of silicate cryptocrystalline phases and sulphate minerals (celestine–barite) and contains calcite grains. The inclusions are distributed in some low-Cr garnet megacrysts and eclogitic garnet. The silicate-sulphate inclusions were crystallised from the late-stage kimberlite melt. Diverse reaction textures are evidences of disequilibrium between the host crystals and polymineralic inclusions and indicate that garnet and the hosted inclusions reacted with the ascending kimberlite melt. The silicate-sulphate inclusions with a thin rim of epidote within eclogitic garnets indicate that a kimberlite melt invaded the garnet and induced partial melting. The studied inclusions allow us to propose three stages of the Grib kimberlite evolution: 1) generation of garnet megacrysts and primary inclusions due to melt metasomatism, 2) reaction of the high-Ti kimberlite melt with garnet megacrysts (including their dissolution) and 3) alteration of the inclusions in garnet after kimberlite ascent.
DS202012-2225
2020
Lee, C., Seoung, D., Cerpa, N.G.Effect of water solubilities on dehydration and hydration in subduction zones and water transport to the deep mantle: implications for natural subduction zones.Gondwana Research, Vol. 89, pp. 287-305. pdfMantlesubduction

Abstract: Understanding water transport by the subducting slab and the corner flow of the mantle wedge is a crucial topic because it is a prime control on seismic tremors, arc-to-intraplate volcanoes as well as on global water distribution in the mantle. However, most of previous studies focused on water transport by the subducting slab and did not quantitatively evaluated the amount of water carried by the corner flow into the deep mantle. Using two-dimensional numerical experiments, we model both the dehydration of the subducting slab and (de)hydration of the mantle wedge and quantify the amount of water transported by both of them. We use the water solubilities of basalt and peridotite derived from laboratory measurements and from thermodynamic calculations, and compare the implications of their differences. Our calculations show that the two models for the water solubilities of basalt result in either abundant or scarce free water through extensive or negligible dehydration of the sub-forearc oceanic crust, leading to a hydrated or a dry cold nose of the mantle wedge, respectively. Further, the oceanic crust of the subducting slab is almost dehydrated prior to reaching a depth of 250 km, regardless of subduction parameters and the models for the water solubilities of basalt. The dehydration depth of the lithospheric mantle of the subducting slab deepens with decreasing slab temperature. The lithospheric mantle of cold subducting slab (e.g., Northeast Japan) experiences partial dehydration at sub-backarc depths and transports the remaining bound water beyond a depth of 250 km, regardless of the models for the water solubilities of peridotite. Deep water transport by the corner flow of the mantle wedge is negligible regardless of the models for the water solubilities of peridotite. The water carried by the lithospheric mantle may be the cause of backarc and intraplate volcanoes in Northeast Asia.
DS202003-0348
2020
Lee, C.W.Y., Cheng, J., Yium Y.C., Chan, K., Lau, D., Tang, W.C., Cheng, K.W,m Kong, T., Hui, T.K.C., Jelezko, F.Correlation between EPR spectra and coloration of natural diamonds.Diamond & Related Materials, Vol. 103, 13p. PdfGlobaldiamond colour

Abstract: White diamonds color grading is one of the basic diamond evaluations. The color value based on a scale that ranges from D to Z, with D being the more colorless and more valuable, among other qualifications. As the diamond grade moves on this scale, its color appears more yellow progressively. This yellowish color, present only in Type I diamonds, is mainly due to the nitrogen related defects such as N3 center and C-center. The current color grading system is based on a visual method, where gemologist compares the sample with a Master Color set. However, this method is very subjective. Several defects responsible for light absorption in diamond are carrying electron spin and appear in Electron Paramagnetic Resonance (EPR) spectrum. In this study, we developed a new EPR based technique for a quantitative measurement of N3 center and C-center in diamond through quantitative EPR spectroscopy. The correlation between EPR spectra and color grades of diamond was established.
DS202012-2226
2011
Lee, C-T.A., Luffi, P., Chin, E.J.Building and destroying continental mantle.Reviews in Advance *** NOTE DATE, Vol. 39, pp. 59-90. pdfMantlecratons

Abstract: Continents, especially their Archean cores, are underlain by thick thermal boundary layers that have been largely isolated from the convecting mantle over billion-year timescales, far exceeding the life span of oceanic thermal boundary layers. This longevity is promoted by the fact that continents are underlain by highly melt-depleted peridotites, which result in a chemically distinct boundary layer that is intrinsically buoyant and strong (owing to dehydration). This chemical boundary layer counteracts the destabilizing effect of the cold thermal state of continents. The compositions of cratonic peridotites require formation at shallower depths than they currently reside, suggesting that the building blocks of continents formed in oceanic or arc environments and became "continental" after significant thickening or underthrusting. Continents are difficult to destroy, but refertilization and rehydration of continental mantle by the passage of melts can nullify the unique stabilizing composition of continents.
DS202007-1158
2020
Leelawatanasuk, T., Atichat, W., Pisutha-Arnond, V., Sutthirat, C., Jakkawanvibul, J., GITTwo decades of GIT's ruby and sapphire color standards.incolorMagazine.com, Vol. winter pp. 96-103.Asia, Thailandsapphire colour
DS202009-1640
2020
Lenardic, A., Seales, J., Weller, M.B.Convective and tectonic plate velocities in a mixed heating mantle.Researchgate, July 29p. Pdf doi:101002 /essoar.10503603.1Mantleplate tectonics

Abstract: Mantle convection and, by association, plate tectonics is driven by the transport of heat from a planetary interior. This heat may come from the internal energy of the mantle or may come from the core beneath and in general there will be contributions from both sources. Past investigations of such mixed-mode heating have revealed unusual behavior that confounds our intuition based on boundary layer theory applied to end-member cases. In particular, the addition of internal heat to a bottom-heated system causes a decrease in convective velocity despite an increase in surface heat flow. We investigate this behavior using a suite of numerical experiments and develop a scaling for velocity in the mixed-heating case. We identify a significant planform transition as internal heating increases from sheet-like to plume-like downwellings that impacts both heat flux and convective velocities. More significantly, we demonstrate that increased internal heating leads not only to a decrease in internal velocities but also a decrease in the velocity of the upper thermal boundary layer (a model analog of the Earth's lithosphere). This behavior is connected to boundary layer interactions and is independent of any particular rheological assumptions. In simulations with a temperature-dependent viscosity and a finite yield stress, increased internal heating does not cause an absolute decrease in surface velocity but does cause a decrease in surface velocity relative to the purely bottom or internally heated cases as well as a transition to rigid-lid behavior at high heating rates. The differences between a mixed system and end-member cases have implications for understanding the connection between plate tectonics and mantle convection and for planetary thermal history modeling.
DS202007-1159
2020
Li, W, Yang, Z., Chiaradia, M., Yong, L., Caho, Yu., Zhang, J.Redox state of southern Tibetan mantle and ultrapotassic magmas. Lhasa TerraneGeology, Vol. 48, 7, pp. 733-736. pdfAsia, Tibetalkaline rocks

Abstract: The redox state of Earth’s upper mantle in several tectonic settings, such as cratonic mantle, oceanic mantle, and mantle wedges beneath magmatic arcs, has been well documented. In contrast, oxygen fugacity (graphic) data of upper mantle under orogens worldwide are rare, and the mechanism responsible for the mantle graphic condition under orogens is not well constrained. In this study, we investigated the graphic of mantle xenoliths derived from the southern Tibetan lithospheric mantle beneath the Himalayan orogen, and that of postcollisional ultrapotassic volcanic rocks hosting the xenoliths. The graphic of mantle xenoliths ranges from ?FMQ = +0.5 to +1.2 (where ?FMQ is the deviation of log graphic from the fayalite-magnetite-quartz buffer), indicating that the southern Tibetan lithospheric mantle is more oxidized than cratonic and oceanic mantle, and it falls within the typical range of mantle wedge graphic values. Mineralogical evidence suggests that water-rich fluids and sediment melts liberated from both the subducting Neo-Tethyan oceanic slab and perhaps the Indian continental plate could have oxidized the southern Tibetan lithospheric mantle. The graphic conditions of ultrapotassic magmas show a shift toward more oxidized conditions during ascent (from ?FMQ = +0.8 to +3.0). Crustal evolution processes (e.g., fractionation) could influence magmatic graphic, and thus the redox state of mantle-derived magma may not simply represent its mantle source.
DS202007-1160
2020
Li, W-Y., Yu, H-M., Xu, J., Halama, R., Bell, K., Nan, X-Y., Huang, F.Barium isotopic composition of the mantle: constraints from carbonatites.Geochimica et Cosmochimica Acta, Vol. 278, pp. 235-243.Mantlecarbonatite

Abstract: To investigate the behaviour of Ba isotopes during carbonatite petrogenesis and to explore the possibility of using carbonatites to constrain the Ba isotopic composition of the mantle, we report high-precision Ba isotopic analyses of: (1) carbonatites and associated silicate rocks from the only active carbonatite volcano, Oldoinyo Lengai, Tanzania, and (2) Archean to Cenozoic carbonatites from Canada, East Africa, Germany and Greenland. Carbonatites and associated phonolites and nephelinites from Oldoinyo Lengai have similar ?137/134Ba values that range from +0.01 to +0.03‰, indicating that Ba isotope fractionation during carbonatite petrogenesis is negligible. The limited variation in ?137/134Ba values from ?0.03 to +0.09‰ for most carbonatite samples suggests that their mantle sources have a relatively homogeneous Ba isotopic composition. Based on the carbonatites investigated in this work, the average ?137/134Ba value of their mantle sources is estimated to be +0.04?±?0.06‰ (2SD, n?=?16), which is similar to the average value of +0.05?±?0.06‰ for mid-ocean ridge basalts. The lower ?137/134Ba value of ?0.08‰ in a Canadian sample and higher ?137/134Ba values of +0.14‰ and?+?0.23‰ in two Greenland samples suggest local mantle isotopic heterogeneity that may reflect the incorporation of recycled crustal materials in their sources.
DS202006-0931
2020
Li, W-Ye., Yu, H-M., Xu, J., Halama, R., Bell, K., Nan, X-Y., Huang, F.Barium isotopic composition of the mantle: constraints from carbonatites.Geochimica et Cosmochimica Acta, Vol. 278, pp. 235-243. pdfAfrica, Tanzania, Canada, Europe, Germany, Greenlanddeposit - Oldoinyo Lengai

Abstract: To investigate the behaviour of Ba isotopes during carbonatite petrogenesis and to explore the possibility of using carbonatites to constrain the Ba isotopic composition of the mantle, we report high-precision Ba isotopic analyses of: (1) carbonatites and associated silicate rocks from the only active carbonatite volcano, Oldoinyo Lengai, Tanzania, and (2) Archean to Cenozoic carbonatites from Canada, East Africa, Germany and Greenland. Carbonatites and associated phonolites and nephelinites from Oldoinyo Lengai have similar ?137/134Ba values that range from +0.01 to +0.03‰, indicating that Ba isotope fractionation during carbonatite petrogenesis is negligible. The limited variation in ?137/134Ba values from ?0.03 to +0.09‰ for most carbonatite samples suggests that their mantle sources have a relatively homogeneous Ba isotopic composition. Based on the carbonatites investigated in this work, the average ?137/134Ba value of their mantle sources is estimated to be +0.04?±?0.06‰ (2SD, n?=?16), which is similar to the average value of +0.05?±?0.06‰ for mid-ocean ridge basalts. The lower ?137/134Ba value of ?0.08‰ in a Canadian sample and higher ?137/134Ba values of +0.14‰ and?+?0.23‰ in two Greenland samples suggest local mantle isotopic heterogeneity that may reflect the incorporation of recycled crustal materials in their sources.
DS202011-2050
2020
Limanov, E.V., Butvina, V.G., Safonov, O.G., Van, K.V., Aranovich, L. Ya.Phlogopite formation in the orthopyroxene-garnet system in the presence of H2O-KCL fluid to the processes of mantle metasomatism.Doklady Earth Sciences, Vol. 494, 1, pp. 713-717.Russiametasomatism

Abstract: The results of experimental studies are presented for reactions in the orthopyroxene-garnet-phlogopite system in the presence of H2O-KCl fluid at 3-5 GPa and 900-1000°C, which model the processes of phlogopite formation in garnet peridotites and pyroxenites during alkaline metasomatism of the upper mantle. The experiments demonstrated regular variations in the composition of garnet, pyroxenes, and phlogopite depending on the KCl content of the fluid. With increasing KCl content of the fluid, enstatite and garnet become unstable, the Al2O3 content of enstatite decreases, and the amount of grossular and knorringite components in garnet are maximum at a KCl content of ~10 mol %. Our results illustrate well the regular variations in the compositions of the coexisting minerals and their zoning in phlogopite-bearing peridotites of the lithospheric mantle.
DS202005-0747
2020
Lin, J-F., Mao, Z., Yang, J., Fu, S.Elasticity of lower-mantle bridgmanite.Nature, Vol. 564, 7736, doi:10.1038/s41586-018-0741-7Mantlebridgmanite
DS202006-0932
2020
Liu, J., Pearson, D.G., Shu, Q., Sigurdsson, H., Thomassot, E., Alard, O.Dating post-Archean lithospheric mantle: insights from Re-Os and Lu-Hf isotopic systematics of the Cameroon volcanic line peridotites.Geochimica et Cosmochimica Acta, Vol. 278, pp. 177-198.Africa, Cameroonperidotites

Abstract: Highly depleted Archean peridotites have proven very amenable to Re-Os model age dating. In contrast, due to the increasing heterogeneity of mantle Os isotope compositions with time, the Re-Os system has not been as effective in dating post-Archean peridotites. The timing of depletion and accretion of post-Archean lithospheric mantle around cratons is important to understand within the context of the evolution of the continents. In an attempt to precisely date post-Archean peridotite xenoliths, we present a study of the petrology, mineralogy and geochemistry, including whole-rock Re-Os isotopes, highly siderophile elements and clinopyroxene-orthopyroxene Sr-Nd-Hf isotopes of peridotite xenoliths from Lake Nyos in the Cameroon Volcanic Line (CVL). Eight Nyos peridotite xenoliths, all fresh spinel lherzolites, are characterized by low to moderate olivine Fo contents (88.9-91.2) and low spinel Cr# (8.4-19.3), together with moderate to high whole-rock Al2O3 contents (2.0-3.7%). These chemical characteristics indicate that they are mantle residues of a few percent to <20% partial melting. However, trace element patterns of both clinopyroxene and orthopyroxene are not a pristine reflection of melt depletion but instead show various extents of evidence of metasomatic enrichment. Some of the samples contain orthopyroxene with 143Nd/144Nd lower than its coexisting clinopyroxene, which is best explained by recent short-timescale alteration, most likely by infiltration of the host basalt. Because of these metasomatic effects, the Sr-Nd isotope systematics in pyroxenes cannot sufficiently reflect melt depletion signatures. Unlike Sr-Nd isotopes, the Lu-Hf isotope system is less sensitive to recent metasomatic overprinting. Given that orthopyroxene hosts up to 33% of the Lu and 14% of the Hf in the whole rock budget of these rocks and has 176Hf/177Hf similar to, or higher than, coexisting clinopyroxene, it is necessary to reconstruct a whole-rock Lu-Hf isochron in order to constrain the melt depletion age of peridotites. The reconstructed Nyos Lu-Hf isochron from ortho- and clinopyroxenes gives an age of 2.01?±?0.18?Ga (1?), and when olivine and spinel are considered, is 1.82?±?0.14?Ga (1?). Both ages are identical within error, and they are within error of the alumina-187Os/188Os pseudo-isochron ages (1.2-2.4?Ga) produced on the peridotites from Lake Nyos, consistent with their oldest rhenium depletion Os model ages (2.0?Ga). We conclude that the Nyos peridotites, and the lithospheric mantle that they represent, were formed at ?2.0?Ga, indicating that the reconstructed whole-rock Lu-Hf isotope system can be a powerful radiometric dating tool that is complementary to and in some instances, more precise than the Re-Os isotope system in dating well-preserved post-Archean peridotites. The recognition of ?2.0?Ga subcontinental lithospheric mantle (SCLM) in the Nyos area suggests that the Nyos region was assembled as a Paleoproterozoic block, or that it represents fragments of the SCLM from the nearby Paleoproterozoic domain juxtaposed through collisional emplacement during the Pan African Orogeny. With regards to the origin of the CVL, our data reveal that the Hf isotopic compositions of the Nyos peridotites are too radiogenic to be the main source of the CVL basalts.
DS202010-1857
2020
Liu, S., Ding, L., Fan, H-R., Yang, K-F., Tang, Y-W. She, H-D, Hao, M-z.Hydrothermal genesis of Nb mineralization in the giant Bayan Obo REE-Nb-Fe deposit ( China): implicated by petrography and geochemistry of Nb-bearing minerals.Precambrian Research, Vol. 348, 105864 24p. PdfChinadeposit - Bayan Obo

Abstract: The Bayan Obo REE-Nb-Fe deposit, which reserves the current largest REE resources globally, also hosts over 70% of China’s Nb resources. Unlike many world-class carbonatite-related Nb deposits (e.g. Morro dos Seis Lagos and Araxá, Brazil) with igneous or secondary origin, Nb was mainly stored in Nb-bearing minerals (aeschynite, ilmenorutile, baotite, fergusonite etc.) of hydrothermal origin at Bayan Obo, supported by evidence from petrography, element and isotopic geochemistry. Although igneous fersmite and columbite were occasionally discovered in local carbonatite dykes, the Mesoproterozoic and Paleozoic hydrothermal metasomatism occurred in the ore-hosting dolomite, related to carbonatite intrusion and the closure of Paleo-Asian Ocean respectively, has played a more significant role during the ultimate Nb enrichment. REE, however, was significantly enriched during both the carbonatite-related magmatic and hydrothermal processes. Consequently, there was differentiated mineralization between REE and Nb in the carbonatite dykes and the ores. Niobium mineralization at Bayan Obo is rather limited in Mesoproterozoic carbonatite, whereas more extensive in the metasomatized ore-hosting dolomite, and generally postdating the REE mineralization at the same stage. According to mineral geochemistry, Bayan Obo aeschynite was classified into 3 groups: aeschynite-(Nd) with convex REE patterns (Group 1); aeschynite-(Ce) (Group 2) and nioboaeschynite (Group 3) with nearly flat REE patterns. Aeschynite (Group 1), ilmenorutile and fergusonite precipitated from Paleozoic hydrothermal fluids with advanced fractionation of Ce-rich REE minerals. The Mesoproterozoic hydrothermal Nb mineralization, represented by aeschynite (Group 3) and baotite, occurred postdating REE mineralization at same stage. Besides, fersmite and aeschynite (Group 2) precipitated from the Mesoproterozoic REE-unfractionated melt and hydrothermal fluids, respectively. All above Nb-bearing minerals exhibit extreme Nb-Ta fractionation as a primary geochemical characteristic of mantle-derived carbonatite. The forming age of the aeschynite megacrysts (Group 1) has not been accurately determined. However, the potential age was constrained to ~430 Ma or alternatively ~270-280 Ma subjected to subduction and granite activity, respectively. These aeschynite crystals inherited REEs from multiphase former REE mineralization, with an intermediate apparent Sm-Nd isochron age between the Mesoproterozoic and the Paleozoic REE mineralization events.
DS202002-0203
2020
Liu, S., Fan, H-R., Groves, D.I., Yang, K-F, Yang, Z-F., Wang, Q-W.Multiphase carbonatite related magmatic and metasomatic processes in the genesis of the ore-hosting dolomite in the giant Bayan Obo REE-Nb-Fe deposit.Lithos, in press available, 96p. PdfChinacarbonatite

Abstract: The origin of dolomite that hosts the Bayan Obo REE-Nb-Fe deposit (57.4 Mt.@6% REE2O3, 2.16 [email protected]% Nb2O5, and >1500 Mt.@35% iron oxides) has been controversial for decades, but it is integral to understanding of the genesis of this giant deposit. In this study, based on the textures and in situ major and trace element composition of its carbonates, the dolomite was proved to be initially generated from magnesio-ferro?carbonatite melts. It subsequently experienced magmatic-hydrothermal alteration and recrystallization in a low strain environment, caused by calcio?carbonatitic fluids, with formation of finer-grained dolomite, interstitial calcite and increasing amounts of associated fluorocarbonates. Available stable isotope analyses indicate that the recrystallized ore-hosting dolomite has higher ?13C and ?18O ratios compared to its igneous coarse-grained precursor. Rayleigh fractionation during the recrystallization process, rather than crustal contamination, played a major role in the highly-variable stable isotope composition of carbonates in the dolomite. Low-T alteration increased variability with apparently random increases in ?18O within carbonates. The REE, Ba and Sr were added simultaneously with the elevated (La/Yb)cn from magnesio-ferro?carbonatite melts to calcio?carbonatitic fluids, and to carbonatite-derived aqueous fluids, through which extensive fluorine metasomatism and alkali alteration overlapped the recrystallization of the ore-hosting dolomite. Therefore, the multi-stage REE mineralization at Bayan Obo is closely related to metasomatism by calcio?carbonatitic fluids of previously-emplaced intrusive magnesio-ferro?carbonatite bodies during late evolution of the Bayan Obo carbonatite complex. Then, the ore-hosting dolomitic carbonatite was subjected to compressive tectonics during a Paleozoic subduction event, and suffered intense, largely brittle, deformation, which partially obscured the earlier recrystallization process. The complex, multi-stage evolution of the ore-hosting dolomite is responsible for the uniqueness, high grade and giant size of the Bayan Obo deposit, the world's largest single REE resource with million tonnes of REE oxides.
DS202001-0026
2019
Live ScienceEarth's magnetic north pole continues drifting, crosses prime meridian.LiveScience.com, Dec 18, 1p.Mantlemagnetics
DS202002-0204
2019
Lobanov, S.S., Holtgrewe, N., Ito, G., Badro, J., Piet, H., Babiel, F., Lin, J-F., Bayarjargal, L., Wirth, R., Schrieber, A., Goncharov, A.F.Blocked radiative heat transport in the hot pyrolitic lower mantle.Researchgate.com, 32p. PdfMantlegeothermometry

Abstract: The heat flux across the core-mantle boundary (QCMB) is the key parameter to understand the Earth/s thermal history and evolution. Mineralogical constraints of the QCMB require deciphering contributions of the lattice and radiative components to the thermal conductivity at high pressure and temperature in lower mantle phases with depth-dependent composition. Here we determine the radiative conductivity (krad) of a realistic lower mantle (pyrolite) in situ using an ultra-bright light probe and fast time-resolved spectroscopic techniques in laser-heated diamond anvil cells. We find that the mantle opacity increases critically upon heating to ~3000 K at 40-135 GPa, resulting in an unexpectedly low radiative conductivity decreasing with depth from ~0.8 W/m/K at 1000 km to ~0.35 W/m/K at the CMB, the latter being ~30 times smaller than the estimated lattice thermal conductivity at such conditions. Thus, radiative heat transport is blocked due to an increased optical absorption in the hot lower mantle resulting in a moderate CMB heat flow of ~8.5 TW, at odds with present estimates based on the mantle and core dynamics. This moderate rate of core cooling implies an inner core age of about 1 Gy and is compatible with both thermally- and compositionally-driven ancient geodynamo.
DS202008-1416
2018
Lobatlamang, S., Brennan, M., Davidson, J., Rogers, A.Discovery of the KX36 kimberlite.Botswana Journal of Earth Sciences, Vol. 7, pp. 29-34. pdfAfrica, Botswanadeposit - KX36

Abstract: The KX36 kimberlite pipe is situated in the southeastern part of Central Kalahari Game Reserve (CKGR), Botswana, approximately 60 km from the known Gope and Kikao kimberlite fields (see figure 1).The kimberlite is covered by 75m of Kalahari sand, has a surface area of 3.6 Ha at the base of the sand cover and was discovered by Petra Diamonds Botswana (Pty) Ltd in 2008. Application of modern geophysical techniques (Ultra hi-resolution low level flying Xcalibur magnetics) and improved sampling method led to the discovery of KX36.The kimberlite was emplaced into the Karoo Supergroup, which comprised the older sedimentary rocks (300 - 185 Ma) overlain by the flood basalts (185Ma). The Karoo Supergroup rocks are overlain by approximately 80m of Kalahari Group sediments.
DS202008-1417
2019
Lobe, P.R., Nhleko, A.S., Mtegha, H.Evaluation of government equity participation in the minerals sector of Tanzania from 1996-2015.The Journal of the Southern African Insitute of Mining and Metallurgy, Vol. 119, Feb. 10p. PdfAfrica, Tanzaniafinancing

Abstract: Government's equity role in the minerals sector is one of the nationalist measures implemented in order to ensure greater control and management of a country's mineral resources. This paper evaluates the Tanzanian government's equity participation in the minerals sector from 1996 to 2015. The research methodology included determination of the number of mineral rights, minimum allowable exploration expenditures in prospecting licences (PLs), and forms of equity role of the government. Data was collected and analysed for PLs, mining licences (MLs), and special mining licences (SMLs). The study revealed a number of challenges faced by the Tanzanian government as regards its equity strategy in the mineral sector. One of the major challenges was the secrecy surrounding agreements and contracts entered into between the government and private sector investors, which were concluded via various business ownership and mineral development projects. This secrecy resulted in non-transparency and lack of accountability in the mining industry. The financial benefits accruing to the government were inadequately realized, evident through inconsistent payments of corporate income tax and mining royalties by the mining companies. Furthermore, the government does not have solid mechanisms and frameworks for assessing non-financial benefits, thus it is difficult to measure the impact of these factors. It is recommended that the Tanzanian government review the Mining Act and Regulations of 2010 to include the provision of solid mechanisms and frameworks for all forms of government equity role.
DS202010-1858
2016
Lorenz, V. Suhr, P., Suhr, S.Phreatomagmatic maar-diatreme volcanoes and their incremental growth: a model.IN: Nemeth, K., Carrasco-Nunez, G., Aranda-Gomez, J.J., Smith, I.E.M. eds. Monogenetic volcanism GSL Special Volume, Vol 446, 31p. Pdf * note dateEurope, Germany , United States, Australia, Mexicomaars

Abstract: We report here a growth model for phreatomagmatic maar-diatreme volcanoes with respect to the number of eruptions documented in the tephra beds of maar tephra rings and the upper bedded diatreme facies. We show that the number of tephra beds in large diatremes is larger than that in maar tephra rings. Base surges that lack sufficient momentum to scale high maar crater walls deposit their tephra only inside the crater. Thus the total number of eruptions at large maar-diatreme volcanoes will be larger than the number recorded in maar tephra rings. As many maar-diatreme volcanoes erupt dominantly accidental clasts, an incremental mathematical model was applied to study the growth of diatremes. The model is based only on the ejection of distinct amounts of accidental clasts per unit eruption and the chosen number of eruptions is assumed to be identical. The incremental growth of cone-shaped diatremes follows cube-root functions with respect to diameter and depth and slows down with ongoing eruptions. In nature, small and large maar-diatreme volcanoes are formed and filled syn-eruptively, mostly by tephra, depending on the duration and quantity of magma involved in phreatomagmatic eruptions. In our opinion, this mathematical model is the only current method able to model the growth of diatremes.
DS202010-1859
2020
Lorenz, V., Lange, T.The volcanic field of the Swabian Alb in southern Germany. *** GERJber. Mitt. oberrhein. Geol. Ver. N.F. English abstract, Vol. 102, pp. 153-174. 22p. PdfEurope, Germanymelilitite
DS202010-1860
2020
Lorenz, V., Lange, T., Buchel, G.The volcanoes of the Westeifel, Germany. ***GERJber. Mitt. oberrhein. Geol. Ver. N.F. English abstract, Vol. 102, pp. 379-411. 33p. PdfEurope, Germanymaars
DS202001-0027
2019
Lougheed, H.D., McClenaghan, M.B., Layton-Matthews, D., Leybourne, M.I.Evaluation of single use nylon screened sieves for use with fine grained sediment samples.Geological Survey of Canada, Open File 8613, 13p. PdfGlobalsieves
DS202007-1161
2020
Lu, J., Tilhac, R., Griffin, W.L., Zheng, J.P., Xiong, Q., Oliveira, B., O'Reilly, S.Y.Lithospheric memory of subduction in mantle pyroxenite xenoliths from rift related basalts.Earth and Planetary Science Letters, Vol. 544, 116365 14p. PdfAustraliacarbonatite

Abstract: Petrological and geochemical studies have revealed the contribution of garnet pyroxenites in basalt petrogenesis. However, whether primary mantle melts are produced with such signature or acquired it subsequently remains somewhat controversial. We here integrate new major-, trace-element and Sr-Nd-Hf isotopic compositions of garnet pyroxenite xenoliths in Holocene alkali basalts from Lakes Bullenmerri and Gnotuk, Southeastern Australia, to relate their petrogenesis to mantle-wedge melt circulation and subsequent lithospheric evolution. Results show that the clinopyroxenites have lower MgO and Cr2O3 contents than the associated websterites, and range in compositions from depleted LREE patterns and highly radiogenic Nd and Hf isotopic signatures in relatively low-MgO samples (Type 1), to enriched REE patterns with negative HFSE anomalies, unradiogenic Nd and Hf isotopes, and extremely radiogenic Sr-isotopic ratios in samples with higher MgO (Type 2). Such compositional variabilities suggest that these pyroxenites represent segregates from melts derived from a recycled oceanic lithosphere with a potential contribution from pelagic sediments. Variable LREE contents and isotopic compositions between those of Type 1 and 2 clinopyroxenites are observed in amphibole-bearing samples (Type 3), which are interpreted as Type 1-like protoliths metasomatized by the basaltic and carbonatitic melts, possibly parental to Type 2 clinopyroxenites. The lithosphere beneath Southeastern Australia thus has received variable melt contributions from a heterogeneous mantle-wedge source, which notably includes a subducted oceanic slab package that has retained its integrity during subduction. On this basis, we suggest that the compositional heterogeneity and temporal evolution of the subsequent Southeastern Australian basaltic magmatism were probably affected by the presence of pyroxenite fragments in the basalt source and formed by the tectonic reactivation of this lithosphere during Cenozoic rifting. This interpretation is notably consistent with a trend of Nd-Pb isotopes towards EMII in Older Volcanic Provinces (OVP basalts) and limited Sr-Nd-Pb isotopic variations towards HIMU in the Newer Volcanic Provinces (NVP basalts, including the host lavas), which also exhibit low SiO2, high FeO and high CaO/Al2O3 commonly interpreted as due to pyroxenite contributions. Therefore, the identification of a subduction signature in these rift-related lavas attests to a "lithospheric memory" of earlier subduction episodes (as documented by the xenoliths), rather than a reflection of contemporaneous subduction tectonics.
DS202006-0933
2020
Lutz, K,A., Long, M.D., Creasy, N., Deng, J.Seismic anisotropy in the lowermost mantle beneath North America from SKS-SKKS splitting intensity discrepancies.Physics of the Earth and Planetary Interiors, in press available, 51p. PdfUnited States, Canadageophysics - seismics

Abstract: We examined SKS-SKKS splitting intensity discrepancies for phases that sample the lowermost mantle beneath North America, which has previously been shown to exhibit seismic anisotropy using other analysis techniques. We examined data from 25 long-running seismic stations, along with 244 stations of the temporary USArray Transportable Array, located in the eastern, southeastern and western U.S. We identified 279 high-quality SKS-SKKS wave pairs that yielded well-constrained splitting intensity measurements for both phases. Of the 279 pairs, a relatively small number (15) exhibited discrepancies in splitting intensity of 0.4 s or greater, suggesting a contribution to the splitting of one or both phases from anisotropy in the lowermost mantle. Because only a small minority of SK(K)S phases examined in this study show evidence of being affected by lowermost mantle anisotropy, the traditional interpretation that splitting of these phases primarily reflects anisotropy in the upper mantle directly beneath the stations is appropriate. The discrepant pairs exhibited a striking geographic trend, sampling the lowermost mantle beneath the southern U.S. and northern Mexico, while other regions were dominated by non-discrepant pairs. We carried out ray theoretical modeling of simple anisotropy scenarios that have previously been suggested for the lowermost mantle beneath North America, invoking the alignment of post-perovskite due to flow induced by the impingement of the remnant Farallon slab on the core-mantle boundary. We found that our measurements are generally consistent with this model and with the idea of slab-driven flow, but relatively small-scale lateral variations in the strength and/or geometry of lowermost mantle anisotropy beneath North America are also likely present.
DS202008-1418
2020
Lutz, K.A., Long, M.D., Creasy, N., Deng, J.Seismic anisotropy in the lowermost mantle beneath North America from SKS-SKKS splitting intensity discrepancies.Physics of the Earth and Planetary Interiors, Vol. 305, 106504, 15p. PdfUnited Statesgeophysics - seismics

Abstract: We examined SKS-SKKS splitting intensity discrepancies for phases that sample the lowermost mantle beneath North America, which has previously been shown to exhibit seismic anisotropy using other analysis techniques. We examined data from 25 long-running seismic stations, along with 244 stations of the temporary USArray Transportable Array, located in the eastern, southeastern and western U.S. We identified 279 high-quality SKS-SKKS wave pairs that yielded well-constrained splitting intensity measurements for both phases. Of the 279 pairs, a relatively small number (15) exhibited discrepancies in splitting intensity of 0.4 s or greater, suggesting a contribution to the splitting of one or both phases from anisotropy in the lowermost mantle. Because only a small minority of SK(K)S phases examined in this study show evidence of being affected by lowermost mantle anisotropy, the traditional interpretation that splitting of these phases primarily reflects anisotropy in the upper mantle directly beneath the stations is appropriate. The discrepant pairs exhibited a striking geographic trend, sampling the lowermost mantle beneath the southern U.S. and northern Mexico, while other regions were dominated by non-discrepant pairs. We carried out ray theoretical modeling of simple anisotropy scenarios that have previously been suggested for the lowermost mantle beneath North America, invoking the alignment of post-perovskite due to flow induced by the impingement of the remnant Farallon slab on the core-mantle boundary. We found that our measurements are generally consistent with this model and with the idea of slab-driven flow, but relatively small-scale lateral variations in the strength and/or geometry of lowermost mantle anisotropy beneath North America are also likely present.
DS202005-0748
2020
Mackensie, S., Everingham, J-A., Bourke, P.The social dimensions of mineral exploration. Not specific to diamonds - but interestSEG Discovery ( former NewsLetter), No. 121, April, pp. 16-28.Globalgeoscience

Abstract: Geoscientists are often the first point of contact a local community has with a company conducting mineral exploration. The behavior of the geoscientists and the interest they take in understanding the local community and stakeholders will have ramifications well beyond their direct exploration activities. This article highlights some of the positive and negative impacts exploration can have for local communities (in part drawing on interviews with experienced geoscientists and others involved in exploration). The article explores the increasing complexity of deposits in terms of environmental, economic, social, and political parameters and the increasing scrutiny by local stakeholders and the international community. We argue that, although geoscientists are not social performance specialists, they still need the awareness, tools, and capabilities to understand and manage the social aspects of their exploration activities commensurate with the stage and resourcing of the project. We propose three interrelated aspects of social performance that can be applied during mineral exploration: meaningful and positive engagement, acquiring and documenting a social knowledge base, and strategic investment in the community. Two case studies provide cautionary examples of failure to do so and two case studies highlight how, through careful engagement and strategic collaboration, mutually beneficial and positive relationships can be built from early exploration.
DS202011-2051
2020
Maconachie, R., Conteh, F.M.Artisanal mining and the rationalisation of informality: critical reflections from Liberia.Canadian Journal of Development Studies, Vol. 41, 3, pp. 432-449. pdfAfrica, Liberiaalluvials

Abstract: Across sub-Saharan Africa, artisanal and small-scale mining (ASM) represents a major source of direct and indirect employment. Yet, despite the livelihood benefits and the growing interest from governments, donors and policy makers to formalise ASM, most artisanal miners still operate informally. Focusing on Liberia, this article critically investigates the question of why formalisation efforts continue to fail and argues that the persistence of informality in the sector needs to first be understood as a rational strategy for those who profit from it. Only then can sustainable mining reforms be linked to broader national and international extractive sector policy frameworks.
DS202004-0527
2020
Maltese, A., Mezger, K.The pb isotope evolution of bulk silicate Earth: constraints from its accretion and early differentiation history.Geochimica et Cosmochimica Acta, Vol. 271, pp. 179-193.Mantlemeteorites

Abstract: Constraining the evolution of Pb isotopes in the bulk silicate Earth (BSE) is hampered due to the lack of a direct determination of Earth’s U/Pb and initial Pb isotope composition. All estimates of these parameters are strongly model dependent and most Pb evolution models start with a meteoritic source, i.e., the primordial Pb composition determined in troilite from the Canyon Diablo iron meteorite. During the condensation of the elements in the solar nebula, accretion of the Earth, and its subsequent chemical evolution, the U/Pb was modified. Different models make different assumptions about the timing and extent of this U-Pb fractionation during Earth’s chemical evolution that cannot always be related to known global geological processes at the time of this modification. This study explores geochemical constraints that can be related to known geological processes to derive an internally consistent model for the evolution of the U-Th-Pb systematics of the silicate Earth. Lead is chalcophile, moderately volatile, and as a result strongly depleted in the BSE compared to primitive meteorites. Any process affecting the abundance and isotope composition of Pb in Earth throughout its early history has to be consistent with the abundance of elements with similar chemical and physical properties in the same reservoir. The abundances of refractory to moderately and highly volatile elements in the BSE imply that the proto Earth was highly depleted in volatile elements, and therefore evolved with a very high U/Pb (238U/204Pb?=?µ???100) prior to collision with the Moon-forming giant impactor. This impactor had close to chondritic abundances of moderately to highly volatile elements and delivered most of Earth’s volatile elements, including the Pb budget. Addition of this volatile-rich component caused oxidation of Earth’s mantle and allowed effective transfer of Pb into the core via sulfide melt segregation. Sequestration of Pb into the core therefore accounts for the high µBSE, which has affected ca. 53% of Earth’s Pb budget. In order to account for the present-day Pb isotope composition of BSE, the giant impact must have occurred at 69?±?10 Myr after the beginning of the solar system. Using this point in time, a model-derived µ-value and the corresponding initial Pb isotope composition of BSE, a single stage Pb isotope evolution curve can be deduced. The result is a model evolution curve for BSE in 208Pb-207Pb-206Pb-204Pb-isotope space that is fully consistent with geochemical constraints on Earth’s accretionary sequence and differentiation history. This Pb-evolution model may act as a reference frame to trace the silicate Earth’s differentiation into crust and mantle reservoirs, similar to the CHUR reference line used for other radio-isotope systems. It also highlights the long-standing Th/U paradox of the ancient Earth.
DS202012-2227
2013
Manfredi, T.K., Nes, A.C.B., Perceira, V.P., Barbanson, L.The parasite-(Ce) mineralization associated with the Fazenda Varela carbonatite ( Correia Pinto, SC).Pesquisas Geosciencias, Dec. 14p. PdfSouth America, Brazil, Santa Catarinadeposit - Fazenda

Abstract: The Fazenda Varela carbonatite is part of the Lages alkaline complex (Late Cretaceous). The carbonatite occurs as abundant veins that cut the sandstones of the Rio Bonito Formation which are strongly brecciated and metasomatized. Petrography, geochemistry, X-ray diffraction, scanning electron microscopy and electron microprobe data allowed the identification and classification of REE fluorcarbonates. The carbonatite is composed essentially by ankerite and Fe-dolomite and was strongly affected for tardi and post magmatic events. The hydrothermal fluids percolated through fractures and grain boundaries and formed hydrothermal domains composed of barite, apatite, quartz, calcite, Fe-dolomite, and parisite-(Ce). In these domains, parisite-(Ce) occurs as well-developed fibrous to fibroradiated crystals. Parisite-(Ce) also occurs in hydrothermal veins that cut the metasomatized host rock. The parisite-(Ce) crystals are heterogeneous, occur in syntaxial growth with synchysite-(Ce), and have excess of Ca and REE and F depletions in relation to an ideal composition. The parasite-(Ce) mineralization formed from a fluid with low F activity that interacted with the rock and leached preferentially the LREE, which were likely transported as chlorine complexes.
DS202012-2228
2020
Marimon, R.S., Trouw, R.A.J., Dantas, E.L.Significance of age periodicity in the continental crust record: the Sao Francisco craton and adjacent Neoporterozoic orogens as a case study.Gondwana Research, Vol. 86, pp. 144-163. pdfSouth America, Brazilmagmatism

Abstract: The São Francisco Craton, in Brazil, together with adjacent orogenic systems formed during Gondwana assemblage, are well-suited for the study of crustal growth processes. The region's geological history is marked by a series of complete tectono-metamorphic cycles, from the Archean to late Neoproterozoic, comprising arc-related magmatism followed by continental collisions and ultimately post-tectonic igneous events and rifting. In this contribution, a comprehensive isotopic database was compiled from the literature, composed mainly of high-quality U-Pb magmatic and metamorphic ages (ca. 1000), together with Lu-Hf (ca. 1300) and Sm-Nd (ca. 300) data. Using this database, combined with a tectonic/geochemical synthesized review of the region, it is possible to test which of the available contending models can better explain the apparent periodicity in the formation of the continental crustal. Some interpreted the peaks and troughs in the crustal age record as periods of increased magmatic production, controlled by periodic mantellic events. Another hypothesis is that subduction-related rocks are shielded from tectonic erosion after continental amalgamation, the peaks thus reflecting enhanced preservation potential. The latter hypothesis is favored, as the variability regarding the timing of arc-related peak magmatic production (U-Pb age peaks) from different tectonic provinces around the globe and in the considered regions, coupled to the fact that peak arc-production is always closely followed in time by major continental amalgamations (supercontinent formation), precludes a unified global causation effect, such as mantellic overturns or slab avalanches, and supports the preservation bias hypothesis. Furthermore, the worldwide (including the São Francisco Craton) occurrence of plume-related magmatism is concentrated during the periods of supercontinent break-up (i.e. after major collisions), which better relates to a top-down control on mantle convection and opposes most of the models that advocate for the primary periodicity of magmatic production, which predict enhanced plume activity slightly prior or concomitant to supercontinent formation events.
DS202006-0934
2020
Marshall, T.GSSA Professional Affairs Portfolio - discussion April 29 and the need to be Professional!GSSA Presentation, https://www.youtube.com /watch?v=Hnwk3lPkMcMGlobalCSR - Professional Development
DS202007-1162
2020
Martelat, J-E., Cardon, H., Lardeaux, J-M., Nicollet, C., Schulmann, K., Pili, E.Geophysical evidence for large scale mullion type structures at the mantle crust interface in southern Madagascar: implications for Neoproterozoic orogeny.International Journal of Earth Science, Vol. 109, 4, pp. 1487-1500.Africa, Madagascartectonics

Abstract: This study uses gravimetric data integrated with recent seismic data published on south Madagascar to investigate geometry of crust-mantle interface. The regional tectonic framework of Madagascar is characterised by anastomosing network of up to 15-km-wide, 600-km-long and north-oriented high-strain zones, which originated during Neoproterozoic convergence. The studied Bouguer anomalies obtained from the International Gravimetric Bureau were high-pass filtered to emphasise short-wavelength gravimetric variations (shorter than 200 km). The Pan-African high-strain zones coincide with the positive gravimetric anomalies suggesting a link with deep seated high-density material. Considering the present-day thickness of the crust (35 km) and its seismic velocity record, the gravimetric anomalies can be visualised as narrow vertical tabular bodies located at the base of the Moho. Modelling further confirmed that such narrow vertical bodies could be stable over geologic time scale since these structures are relatively small (10 to 30 km wide). The vertical tabular bodies possibly reflect material transfer such as vertical motion of sub-crustal weak and possibly partially molten mantle along vertical deformation zones. It is proposed that these structures were initiated by folding of weak mantle-crust interface characterised by low-viscosity contrast between weak mantle and stronger granulitized lower crust during bulk pure shear-dominated horizontal shortening. It is proposed that the cuspate-lobate "mullion-type" geometry mimics rheological inversions of mafic and felsic rocks and shape of folds of variable scale observed in southern Madagascar. The formation of such mega-mullion structures is possibly an expression of "crème brulée" rheological model, where the deformation of the lithosphere is governed by stronger granulitic lower crust and weaker partially molten and/or hydrated mantle.
DS202008-1419
2018
Marx, M.The Orapa discovery - one small step.Botswana Journal of Earth Sciences, Vol. 7, pp. 1-2. pdfAfrica, Botswanadeposit - Orapa

Abstract: I feel tremendously honoured and privileged to be invited to attend the 50thanniversary celebrations of the Orapa discovery. Thank you, Leon Daniels and Debswana. This will be a very emotional and exciting experience for me to return to Orapa after 50 years, where early in the morning of the 21st of April 1967 my team of twelve Motswana explorers and I stepped onto a low calcrete hill littered with kimberlitic indicator minerals. This was not entirely unexpected, as some months earlier Dr Gavin Lamont (the exploration manager) and Jim Gibson (the senior geologist) had detected such minerals during a road sampling survey into this isolated region south of the Makgadigadi Pans. However, what was unexpected was the enormous size of this kimberlite pipe that was destined to become the world-class Orapa diamond mine.
DS202012-2229
2020
Massonne, H-J., Li, B.Zoning of eclogitic garnet cores - a key pattern demonstrating the dominance of tectonic erosion as part of the burial process of worldwide occurring eclogites.Earth-Science Reviews, Vol. 210, 103356 27p. PdfMantleeclogites
DS202006-0935
2020
Matrosova, E.A., Bobrov, A.V., Bindi, L., Pushcharovsky, D.Yu., Irifune, T.Titanium-rich phases in the Earth's transition zone and lower mantle: evidence from experiments in the system Mg)-Si)2-TiO2(+- Al2O3Lithos, Vol. 366-367, 14p. PdfMantlewebsterite, bridgmanite

Abstract: Phase relations in the MgSiO3-MgTiO3 and Mg3Al2Si3O12-MgTiO3 systems were studied at 10-24 GPa and 1600 °C using a high-pressure Kawai-type multianvil apparatus. We investigated the full range of starting compositions for the enstatite-geikielite system to derive a P-X phase diagram and synthesize titanium-bearing phases, such as olivine/wadsleyite, rutile, pyroxene, MgTiSi2O7 weberite, bridgmanite and MST-bridgmanite in a wide pressure range. Olivine and pyroxene in run products are characterized by a low titanium content (<0.6 and <0.3 wt% TiO2, respectively) whereas the content of TiO2 in wadsleyite reaches 2 wt% at 12 GPa. The concentration of Ti in MgTiSi2O7 weberite decreases with pressure from 52 wt% TiO2 at 14 GPa to 43 wt% TiO2 at 18 GPa. Two perovskite-type structures (MgSiO3 bridgmanite and Mg(Si,Ti)O3 bridgmanite) were detected in the studied system. MgSiO3 bridgmanite (Brd) is formed at a pressure of >20 GPa and characterized by significant titanium solubility (up to 13 wt% TiO2 at 24 GPa). Mg(Si,Ti)O3 perovskite is formed at a pressure of >17 GPa. The concentration of TiO2 in this phase varies from 29 wt% to 49 wt%. It was found that addition of Ti to the system moves the boundaries of Ol/Wad phase transformations to lower pressures. Addition of Al to the starting material allows us to simulate the composition of natural Ti-rich garnets and bridgmanites. It is important to note that garnet in the Prp-Gkl system is stable throughout a wide pressure range (10-24 GPa). Al incorporation does not affect the distribution of titanium between two types of bridgmanite. It is shown that high contents of Ti stabilize bridgmanite-like compounds at considerably lower pressure than that at the lower mantle/transition zone boundary. Our experiments simulate the composition of natural Ti-rich primary garnet found in eclogite from the Sulu ultrahigh-pressure (UHP) terrane.
DS202008-1420
2020
Matrosova, E.M., Bobrov, A.V., Bindi, L., Pushcharovsky, D.Yu., Irifune, T.Titanium rich phases in the Earth's transition zone and lower mantle: evidence from experiments in the system MgO-SiO2-TiO2(+-Al2O3) at 10-24 Gpa and 1600 C.Lithos, Vol. 366-367 1055539 14 p. pdfMantlebridgemanite

Abstract: Phase relations in the MgSiO3-MgTiO3 and Mg3Al2Si3O12-MgTiO3 systems were studied at 10-24 GPa and 1600 °C using a high-pressure Kawai-type multianvil apparatus. We investigated the full range of starting compositions for the enstatite-geikielite system to derive a P-X phase diagram and synthesize titanium-bearing phases, such as olivine/wadsleyite, rutile, pyroxene, MgTiSi2O7 weberite, bridgmanite and MST-bridgmanite in a wide pressure range. Olivine and pyroxene in run products are characterized by a low titanium content (<0.6 and <0.3 wt% TiO2, respectively) whereas the content of TiO2 in wadsleyite reaches 2 wt% at 12 GPa. The concentration of Ti in MgTiSi2O7 weberite decreases with pressure from 52 wt% TiO2 at 14 GPa to 43 wt% TiO2 at 18 GPa. Two perovskite-type structures (MgSiO3 bridgmanite and Mg(Si,Ti)O3 bridgmanite) were detected in the studied system. MgSiO3 bridgmanite (Brd) is formed at a pressure of >20 GPa and characterized by significant titanium solubility (up to 13 wt% TiO2 at 24 GPa). Mg(Si,Ti)O3 perovskite is formed at a pressure of >17 GPa. The concentration of TiO2 in this phase varies from 29 wt% to 49 wt%. It was found that addition of Ti to the system moves the boundaries of Ol/Wad phase transformations to lower pressures. Addition of Al to the starting material allows us to simulate the composition of natural Ti-rich garnets and bridgmanites. It is important to note that garnet in the Prp-Gkl system is stable throughout a wide pressure range (10-24 GPa). Al incorporation does not affect the distribution of titanium between two types of bridgmanite. It is shown that high contents of Ti stabilize bridgmanite-like compounds at considerably lower pressure than that at the lower mantle/transition zone boundary. Our experiments simulate the composition of natural Ti-rich primary garnet found in eclogite from the Sulu ultrahigh-pressure (UHP) terrane.
DS202002-0205
2019
Mazuera, F., Schmitz, M., Escalona, A., Zelt, C., Levander, A.Lithospheric structure of northwestern Venezuela from wide angle seismic data: implications for the understanding of continental margin evolution.Journal of Geophysical Research: Solid Earth, Vol. 124, 12, pp. 13124-131249. ( open access)South America, Venezuelageophysics - seismic

Abstract: Northwestern Venezuela is located in the complex deformation zone between the Caribbean and South American plates. Several models regarding the lithospheric structure of the Mérida Andes have been proposed. Nevertheless, they lack relevant structural information in order to support the interpretation of deeper structures. Therefore, a 560?km?long refraction profile across the northern part of Mérida Andes, oriented in a NNW direction, covering areas from the Proterozoic basement in the south, to both Paleozoic and Meso?Cenozoic terranes of northwestern Venezuela to the north, is analyzed in this contribution. Thirteen land shots were recorded by 545 short?deployment seismometers, constraining P wave velocity models from first?arrival seismic tomography and layer?based inversion covering the whole crust in detail, with some hints to upper mantle structures. The most prominent features imaged are absence of a crustal root associated to the Mérida Andes, as the Northern Andes profile is located marginal to the Andean crustal domain, and low?angle subduction of the Caribbean oceanic slab (~10-20°) beneath northwestern South America. Further crustal structures identified in the profile are (a) crustal thinning beneath the Falcón Basin along the western extension of the Oca?Ancón fault system interpreted as a back?arc basin; (b) suture zones between both the Proterozoic and Paleozoic provinces (Ouachita?Marathon?related suture?), and Paleozoic and Meso?Cenozoic terranes (peri?Caribbean suture) interpreted from lateral changes in seismic velocity; and (c) evidence of a deep Paleozoic(?) extensional basin, underlying thick Mesozoic and Cenozoic sequences (beneath the Guárico area).
DS202002-0206
2020
McCammon, C., Bureau, H., Cleaves II, H.J., Cottrell, E., Dorfman, S.M., Kellogg, L.H., Li, J., Mikhail, S., Moussallam, Y., Sanloup, C., Thomson, A.R., Brovarone, A.V.Deep Earth carbon reactions through time and space. ( mentions diamond)American Mineralogist, Vol. 105, pp. 22-27.Mantlesubduction

Abstract: Reactions involving carbon in the deep Earth have limited manifestations on Earth's surface, yet they have played a critical role in the evolution of our planet. The metal-silicate partitioning reaction promoted carbon capture during Earth's accretion and may have sequestered substantial carbon in Earth's core. The freezing reaction involving iron-carbon liquid could have contributed to the growth of Earth's inner core and the geodynamo. The redox melting/freezing reaction largely controls the movement of carbon in the modern mantle, and reactions between carbonates and silicates in the deep mantle also promote carbon mobility. The 10-year activity of the Deep Carbon Observatory has made important contributions to our knowledge of how these reactions are involved in the cycling of carbon throughout our planet, both past and present, and has helped to identify gaps in our understanding that motivate and give direction to future studies.
DS202003-0349
2019
McClure, S.F., Moses, T.M., Shigley, J.E.The geographic origin dilemma.Gems & Gemology, Vol. 55, 4, pp. 457-463.Globalgemstones

Abstract: Welcome to the Winter 2019 edition of Gems & Gemology. This issue is special in that it is devoted exclusively to one timely subject: the determination of geographic origin for specific colored stones. Geographic origin determination is one of the most pressing issues facing the industry—a subject with many facets and complexities that should be addressed if the discussion is to be thorough. As part of GIA’s consumer protection mission of ensuring the public trust in gems and jewelry, our purpose with this issue is to lay out what we know about determining geographic origin and how we arrive at those opinions. These articles will present every aspect of geographic origin as these authors understand it—including full transparency on the approaches and testing methods typically applied in GIA’s gemological laboratories. We intend for this issue to promote healthy and useful discussion and debate—fueled by our collective interest in bringing more understanding and consistency to the reporting of the geographic origin of colored stones.
DS202003-0350
2019
McClure, S.F., Moses, T.M., Shigley, J.E.What's next .. Future of geographic origin determination.Gems & Gemology, Vol. 55, 4, p. 682.GlobalGIA

Abstract: GIA’s field gemology program was established in late 2008 to support research on geographic origin determination of colored gemstones. By building and maintaining an extensive collection of gem materials with known origins, GIA’s research scientists have been able to study and analyze rubies, sapphires, emeralds, and other gemstones using the best available reference samples. This has led to improved origin determination services while supporting numerous research and education projects. To date the collection has accumulated during more than 95 field expeditions on six continents and currently includes more than 22,000 samples. GIA’s field gemology efforts require a thorough understanding of the gem trade, including the evolution of gemstone deposits and the development of treatments. It is important to recognize potential new deposits and gemstone enhancement procedures immediately because they can change rapidly and leave a lasting impact on the trade. Field expeditions also involve documenting the mines and local conditions. These factors provide context for the gemstones and are becoming increasingly important in the eyes of the public.
DS202012-2230
2020
McDannell, K.T., Flowers, R.M.Vestiges of the ancient: deep-time noble gas thermochronology.Elements, Vol. 16, pp. 325-330.Canada, Nunavut, Southampton Island, Africa, Kaapvaalcraton

Abstract: Ancient rocks have survived plate tectonic recycling for billions of years, but key questions remain about how and when they were exhumed to the surface. Constraining exhumation histories over long timescales is a challenge because much of the rock record has been lost to erosion. Argon and helium noble gas thermochronology can reconstruct deep-time <350 °C thermal histories by using the distinct temperature sensitivities of minerals such as feldspar, zircon, and apatite, while exploiting grain size and radiation damage effects on diffusion kinetics. Resolution of unique time-temperature paths over long timescales requires multiple chronometers, appropriate kinetic models, and inverse simulation techniques to fully explore and constrain possible solutions. Results suggest that surface histories of ancient continental interiors are far from uninteresting and may merely be misunderstood.
DS202012-2231
2020
McGuinness, C.D., Wassell, A.M., Lanigan, P.M.P., Lynch, S.A.Seperation of natural from laboratory-grown diamond using time -gated luminescence imaging.Gems & Gemology, Vol. 56, 2, summer pp. 220-229. pdfGloballuminescence
DS202008-1421
2019
McKechnie, W.F.Diamond exploration and mining in southern Africa: some thoughts on past, current, and possible future trends.The Journal of the Southern African Insitute of Mining and Metallurgy, Vol. 119, Feb, 9p. PdfAfrica, South Africa, Zimbabwe, Namibia, Angola, DRC, Lesotho, Botswana, eSwatiniproduction

Abstract: Southern Africa is generally thought to be well explored, with only limited potential for major new diamond discoveries. However, Chiadzwa in Zimbabwe and reports of a significant new kimberlite find in Angola are testimony to the dangers attached to an attitude that 'there is nothing left to find'. Since the major discoveries in the central interior of South Africa in the 1870s, diamond exploration in the region has been led by market and political factors that influence the key exploration drivers of opportunity and value proposition. Unexpected new discoveries by new players always impact on existing producers and, from time to time, denial of opportunity through political or protectionist policies has inhibited investment in exploration. Entrepreneurial exploration appetite in southern Africa will be tempered by the potential value equation and security of investment. Overlaid on this, developments in diamond recovery technologies provide opportunity to reinvigorate current mines and old prospects previously considered too difficult or costly to exploit. Position on the cost curve will remain a key factor for survival in an increasingly competitive environment.
DS202008-1422
2020
McKensie, L., Kilgore, A.H., Peslier, A.D., Brandon, L.A., Schaffer, R.V., Graff, T.G., Agresti, D.G., O'Reilly, S.Y., Griffin, W.L., Pearson, D.G., Hangi, K., Shaulis, B.J.Metasomatic control of hydrogen contents in the layered cratonic mantle lithosphere sampled by Lac de Gras xenoliths in the central Slave craton, Canada.Geochimica et Cosmochimica Acta, in press available, doi.org/101016 /j.gca.2020.07.013 45p. PdfCanada, Northwest Territoriesdeposit - Lac de Gras

Abstract: Whether hydrogen incorporated in nominally anhydrous mantle minerals plays a role in the strength and longevity of the thick cratonic lithosphere is a matter of debate. In particular, the percolation of hydrogen-bearing melts and fluids could potentially add hydrogen to the mantle lithosphere, weaken its olivines (the dominant mineral in mantle peridotite), and cause delamination of the lithosphere's base. The influence of metasomatism on hydrogen contents of cratonic mantle minerals can be tested in mantle xenoliths from the Slave Craton (Canada) because they show extensive evidence for metasomatism of a layered cratonic mantle. Minerals from mantle xenoliths from the Diavik mine in the Lac de Gras kimberlite area located at the center of the Archean Slave craton were analyzed by FTIR for hydrogen contents. The 18 peridotites, two pyroxenites, one websterite and one wehrlite span an equilibration pressure range from 3.1 to 6.6 GPa and include samples from the shallow (? 145 km), oxidized ultra-depleted layer; the deeper (?145-180 km), reduced less depleted layer; and an ultra-deep (? 180 km) layer near the base of the lithosphere. Olivine, orthopyroxene, clinopyroxene and garnet from peridotites contain 30 - 145, 110 - 225, 105 - 285, 2 - 105 ppm H2O, respectively. Within each deep and ultra-deep layer, correlations of hydrogen contents in minerals and tracers of metasomatism (for example light over heavy rare-earth-element ratio (LREE/HREE), high-field-strength-element (HFSE) content with equilibration pressure) can be explained by a chromatographic process occurring during the percolation of kimberlite-like melts through garnet peridotite. The hydrogen content of peridotite minerals is controlled by the compositions of the evolving melt and of the minerals and by mineral/melt partition coefficients. At the beginning of the process, clinopyroxene scavenges most of the hydrogen and garnet most of the HFSE. As the melt evolves and becomes enriched in hydrogen and LREE, olivine and garnet start to incorporate hydrogen and pyroxenes become enriched in LREE. The hydrogen content of peridotite increases with decreasing depth, overall (e.g., from 75 to 138 ppm H2O in the deep peridotites). Effective viscosity calculated using olivine hydrogen content for the deepest xenoliths near the lithosphere-asthenosphere boundary overlaps with estimates of asthenospheric viscosities. These xenoliths cannot be representative of the overall cratonic root because the lack of viscosity contrast would have caused basal erosion of lithosphere. Instead, metasomatism must be confined in narrow zones channeling kimberlite melts through the lithosphere and from where xenoliths are preferentially sampled. Such localized metasomatism by hydrogen-bearing melts therefore does not necessarily result in delamination of the cratonic root.
DS202012-2232
2020
McManus, C.E., McMillan, N.J., Dowe, J., Bell, J.Diamonds certify themselves: multivariate statistical provenance analysis.MDPI Minerals, Vol. 10, 916, doi:10.2290/ min0100916, 12p. PdfGlobalspectroscopy

Abstract: The country or mine of origin is an important economic and societal issue inherent in the diamond industry. Consumers increasingly want to know the provenance of their diamonds to ensure their purchase does not support inhumane working conditions. Governments around the world reduce the flow of conflict diamonds via paper certificates through the Kimberley Process, a United Nations mandate. However, certificates can be subject to fraud and do not provide a failsafe solution to stopping the flow of illicit diamonds. A solution tied to the diamonds themselves that can withstand the cutting and manufacturing process is required. Here, we show that multivariate analysis of LIBS (laser-induced breakdown spectroscopy) diamond spectra predicts the mine of origin at greater than 95% accuracy, distinguishes between natural and synthetic stones, and distinguishes between synthetic stones manufactured in different laboratories by different methods. Two types of spectral features, elemental emission peaks and emission clusters from C-N and C-C molecules, are significant in the analysis, indicating that the provenance signal is contained in the carbon structure itself rather than in inclusions.
DS202012-2233
2020
Melluso, L., Sethna, S.F., Srivastava, R.K.First occurrence of melilite, potassic richterite and tetraferriphlogopite in Deccan Trap- related alkaline rocks, and its petrogenetic significance: the Rajpuri ijolitenephlinite intrusion, Murud, Mumbai area, India.Journal of Mineralogy and Geochemistry, https://doi.org/ 10.1127/njma/2020/0236Indiamelilite
DS202002-0207
2019
Meng, T., Katz, R.F., Rees Jones, D.W.Devolatization of subducting slabs: Part 1: By thermodynamic parameterization and open system effects. ( carbon transport)Geochemistry, Geophysics, Geosystems, Vol. 20, 1, pp. 5667-5690.Mantlesubduction

Abstract: The amount of H2O and CO2 that is carried into deep mantle by subduction beyond subarc depths is of fundamental importance to the deep volatile cycle but remains debated. Given the large uncertainties surrounding the spatio?temporal pattern of fluid flow and the equilibrium state within subducting slabs, a model of H2O and CO2 transport in slabs should be balanced between model simplicity and capability. We construct such a model in a two?part contribution. In this Part I of our contribution, thermodynamic parameterization is performed for the devolatilization of representative subducting materials—sediments, basalts, gabbros, peridotites. The parameterization avoids reproducing the details of specific devolatilization reactions, but instead captures the overall behaviors of coupled (de)hydration and (de)carbonation. Two general, leading?order features of devolatilization are captured: (1) the released volatiles are H2O?rich near the onset of devolatilization; (2) increase of the ratio of bulk CO2 over H2O inhibits overall devolatilization and thus lessens decarbonation. These two features play an important role in simulation of volatile fractionation and infiltration in thermodynamically open systems. When constructing the reactive fluid flow model of slab H2O and CO2 transport in the companion paper Part II, this parameterization can be incorporated to efficiently account for the open?system effects of H2O and CO2 transport.
DS202007-1163
2019
Meshram, R.R., Dora, M.L., Naik, R., Shareef, M., Gopalakrishna, G., Moeshram, T., Baswani, S.R., Randive, K.R.A new find of calc-alkaline lamprophyres in Thanewasna area, western Bastar craton, India.Journal of Earth System Science, Vol. 128, 1, 7p. PdfIndiaminette

Abstract: Lamprophyre dykes within the granitoid and charnockite are reported for the first time from the Western Bastar Craton, Chandrapur district, Maharashtra. It shows porphyritic-panidiomorphic texture under a microscope, characterised by the predominance of biotite phenocrysts with less abundance of amphibole and clinopyroxene microphenocryst. The groundmass is composed more of K-feldspars over plagioclase, amphiboles, clinopyroxene, biotite, chlorite, apatite, sphene and magnetite. The mineral chemistry of biotite and magnesio-hornblende is indicative of minette variety of calc-alkaline lamprophyre (CAL), which is further supported by preliminary major oxides and trace element geochemistry. This unique association of CAL with granitoid provides an opportunity to study the spatio-temporal evolution of the lamprophyric magma in relation to the geodynamic perspective of the Bastar Craton.
DS202008-1423
2020
Meyer, N.A., Stachel, T., Pearson, D.G., Stern, R.A., Harris, J.W.Diamond formation from the lithosphere to the lower mantle revealed by Koffiefontein diamonds.Goldschmidt 2020, 1p. AbstractAfrica, South Africadeposit - Koffiefontein

Abstract: Because of their robust nature, diamonds survive mantle processes and protect occluded minerals since the time of diamond formation. For the Kaapvaal Craton - the archetype for craton formation and evolution - the geochemical signatures of inclusions in Koffiefontein diamonds tell a story from craton formation to evolution and from lithospheric (below about 160 km) to lower mantle (>660 km) environs. We analysed a suite of 94 lithospheric to lower mantle diamonds and their silicate and oxide inclusions. Geochemical results confirm that the diamond substrates are very depleted, with Mg#OL of 91.5-95.0 and a dominance of low-Ca (<1.8 wt% CaO), presumably dunite-derived garnet. The Si-rich nature and preserved high Mg# of the peridotitic diamond substrates beneath Koffiefontein and the formation of KNbO3 (goldschmidtite) from an extremely fractionated melt/fluid indicate that potentially both mantle- and subduction-related fluids are the cause of metasomatism in the Kaapvaal cratonic root. Mantle-like, restricted carbon isotopic compositions of both P- and E-type diamonds (avg. ?13C -5.7 ‰ and -6.6 ‰, respectively) indicate that an abundant, mantle-derived CHO fluid is responsible for diamond formation. Diamonds have a large range in nitrogen concentrations and isotopic compositions, suggesting decoupling from carbon and heterogeneous sources. ?18O of former bridgmanite and ?13C of its host diamond document a purely mantle-derived lower mantle component. Combined, these results reveal a complex and multistage evolution of the Kaapvaal Craton whereby multiple episodes of fluid and melt metasomatism re-enriched the craton already, prior to diamond formation, followed by diamond entrainment in a kimberlite possibly derived from the lower mantle.
DS202006-0936
2020
Mhangara, P., Tsoeleng, L.T., Mapurisa, W.Monitoring the development of artisanal mines in South Africa.Journal of the Southern African Institute of Mining and Metallurgy, Vol. 120, pp. 299- 307. pdfAfrica, South Africaremote sensing
DS202005-0749
2019
Mikhail, S., Crosby, J.C., Stuart, F.M., DiNicola, L., Abernethy, F.A.J.A secretive mechanical exchange between mantle and crustal volatiles revealed by helium isoptopes in 13 C depleted diamonds.Geochemical Perspectives Letters, Vol. 11, pp. 39-43. pdfAfrica, Botswana, South America, French Guianadeposit - Dachine, Orapa

Abstract: Fluid inclusions trapped in fast-growing diamonds provide a unique opportunity to examine the origin of diamonds, and the conditions under which they formed. Eclogitic to websteritic diamondites from southern Africa show 13C-depletion and 15N-enrichment relative to mantle values (?13C = -4.3 to -22.2 ‰ and ?15N = -4.9 to +23.2 ‰). In contrast the 3He/4He of the trapped fluids have a strong mantle signature, one sample has the highest value so far recorded for African diamonds (8.5 ± 0.4 Ra). We find no evidence for deep mantle He in these diamondites, or indeed in any diamonds from southern Africa. A correlation between 3He/4He ratios and 3He concentration suggests that the low 3He/4He are largely the result of ingrowth of radiogenic 4He in the trapped fluids since diamond formation. The He-C-N isotope systematics can be best described by mixing between fluid released from subducted altered oceanic crust and mantle volatiles. The high 3He/4He of low ?13C diamondites reflects the high 3He concentration in the mantle fluids relative to the slab-derived fluids. The presence of post-crystallisation 4He in the fluids means that all 3He/4He are minima, which in turn implies that the slab-derived carbon has a sedimentary organic origin. In short, although carbon and nitrogen stable isotope data show strong evidence for crustal sources for diamond-formation, helium isotopes reveal an unambiguous mantle component hidden within a strongly 13C-depleted system.
DS202006-0937
2020
Mikhailenko, D., Golovin, A., Korsakov, A., Aulbach, S., Gerdes, A., Ragozin, A.Metasomatic evolution of coesite-bearing diamondiferous eclogite from the Udachnaya kimberlite.Minerals, Vol. 10, 4, 24p. PdfRussia, Siberiadeposit - Udachnaya

Abstract: A coesite-bearing diamondiferous eclogite from the Udachnaya kimberlite (Daldyn field, Siberian craton) has been studied to trace its complex evolution recorded in rock-forming and minor mineral constituents. The eclogite sample is composed of rock-forming omphacite (60 vol%), garnet (35 vol%) and quartz/coesite (5 vol%) and contains intergranular euhedral zoned olivine crystals, up to 200 µm long, coexisting with phlogopite, orthopyroxene, clinopyroxene (secondary), K-feldspar, plagioclase, spinel, sodalite and djerfisherite. Garnet grains are zoned, with a relatively homogeneous core and a more magnesian overgrowth rim. The rim zones further differ from the core in having higher Zr/Y (6 times that in the cores), ascribed to interaction with, or precipitation from, a kimberlite-related melt. Judging by pressure-temperature estimates (~1200 °C; 6.2 GPa), the xenolith originated at depths of ~180-200 km at the base of the continental lithosphere. The spatial coexistence of olivine, orthopyroxene and coesite/quartz with K-Na-Cl minerals in the xenolith indicates that eclogite reacted with a deep-seated kimberlite melt. However, Fe-rich olivine, orthopyroxene and low-pressure minerals (sodalite and djerfisherite) likely result from metasomatic reaction at shallower depths during transport of the eclogite by the erupting kimberlite melt. Our results demonstrate that a mixed eclogitic-peridotitic paragenesis, reported previously from inclusions in diamond, can form by interaction of eclogite and a kimberlite-related melt.
DS202012-2234
2020
Mikhailenko, D.S., Stagno, V., Korsakov, A.V., Andreozzi, G.B., Marras, G., Cerantola, V., Malygina, E.V.Redox state determination of eclogite xenoliths from Udachnaya kimberlite pipe ( Siberian craton), with some implications for the graphite/diamond formation.Contributions to Mineralogy and Petrology, Vol. 175, 107, 17p. PdfRussiadeposit - Udachnaya

Abstract: The formation of diamonds within eclogitic rocks has been widely linked to the fate of carbon during subduction and, therefore, referred to conditions of pressure, temperature, and oxygen fugacity (fo2). Mantle-derived eclogite xenoliths from Udachnaya kimberlite pipes represent a unique window to investigate the formation of carbon-free, graphite-diamond-bearing and diamond-bearing rocks from the Siberian craton. With this aim, we exploited oxy-thermobarometers to retrieve information on the P-T-fo2 at which mantle eclogites from the Siberian craton equilibrated along with elemental carbon. The chemical analyses of coupled garnet and omphacitic clinopyroxene were integrated with data on their iron oxidation state, determined both by conventional and synchrotron 57Fe Mössbauer spectroscopy. The calculated fo2s largely vary for each suite of eclogite samples from 0.10 to ? 2.43 log units (?FMQ) for C-free eclogites, from ? 0.01 to ? 2.91 (?FMQ) for graphite-diamond-bearing eclogites, and from ? 2.08 to ? 3.58 log units (?FMQ) for diamond-bearing eclogites. All eclogite samples mostly fall in the fo2 range typical of diamond coexisting with CO2-rich water-bearing melts and gaseous fluids, with diamondiferous eclogites being more reduced at fo2 conditions where circulating fluids can include some methane. When uncertainties on the calculated fo2 are taken into account, all samples essentially fall within the stability field of diamonds coexisting with CO2-bearing melts. Therefore, our results provide evidence of the potential role of CO2-bearing melts as growth medium on the formation of coexisting diamond and graphite in mantle eclogites during subduction of the oceanic crust.
DS202007-1164
2020
Miller, M.S.Mapping Earth's deepest secrets. Core-mantle boundaryScience , Vol. 368, 6496, pp. 1183-1184.Mantlegeophysics - seismics

Abstract: Deep within Earth's interior, at ?2900 km beneath the surface, lies the boundary between the solid silicate rock mantle and the liquid iron-nickel alloy core (the core-mantle boundary). Geophysicists have studied the complex thermal and chemical dynamics that take place in this boundary layer. In the early 20th century, Gutenberg investigated the structure of the lowermost region, or base, of the mantle by recording with only a few seismograms from a small number of large-magnitude earthquakes that occurred thousands of kilometers away (1). The structure of the rocks just above the core-mantle boundary—designated as D? by Jeffreys in 1939 (2)—forms a distinct layer with surprising complexity. Now, on page 1223 of this issue, Kim et al. (3) describe new structural heterogeneities in the lowermost mantle with the use of a learning algorithm that does not require any a priori knowledge of Earth.
DS202010-1861
2020
Mints, M.V., Dokukina, K.A.Age of eclogites formed by the subduction of the mesoarchean oceanic crust (salma, belomorian eclogite province, eastern fennoscandian shield, Russia): a synthesis.Precambrian Research, doi.org/10.1016/j.precamres.2020.105879in press available, 80p. Pdf Russiaeclogites

Abstract: Competing evolutionary models and age of eclogite facies metamorphism, Mesoarchaean, Neoarchaean or Palaeoproterozoic, of the subducted Mesoarchaean oceanic crust (Salma association, Belomorian Eclogite Province) are discussed on a basis of systematic analysis of previously known and newly obtained data. Four main types of zircons were distinguished in eclogites: porous crystals with numerous inclusions from eclogite-metagabbro; wide-rimmed zircons with relict porous cores similar to previous type separated from garnetites; round-oval zircons from eclogite-metagabbronorite that are characteristic for granulite facies rocks and zircons with euhedral oscillatory zoning cores and oval grains that are characteristic for the eclogite facies pillow basalts. Regular changes in REE patterns and in crystallization-recrystallization temperatures of certain domains of the porous zircons display sequence of magmatic and metamorphic events. The???2.9?Ga domains retain magmatic-type REE patterns. Low- and medium-temperature inclusions of prenite, pumpelliite, albite, actinolite, chlorite, diaspore and saponite in garnet and abundant microinclusions of the prenite-pumpelliite and greenschist facies in zircons with LREE-MREE enrichment indicate hydrothermal metamorphism in the spreading ridge and ocean floor at 2.9-2.82?Ga. Disappearance of Ce positive anomaly from REE pattern in zircon, change negative to positive Eu anomaly and LREE-MREE enrichment caused by plagioclase removal and replacement of rutile with sphene evidence eclogite facies metamorphism linked with subduction at 2.82-2.78?Ga. Temperatures in the 700-900?°C range of the round-oval zircons from eclogite-metagabbronorite records the Neoarchaean granulite facies overprint at 2.77-2.70?Ga. Series of the high temperature Palaeoprpoterozoic events was terminated by 2.1-1.7?Ga event marked by the rims with lowest REE that frame all types of zircons. Change from positive to negative Eu anomaly, retrieval of negative Ce anomaly indicate the presence of plagioclase, reduction type of fluids and low water activity characteristic of high-temperature metamorphism under stretching condition and mantle-plume activity. The deep reworking of the Sm-Nd isotope system in the Belomorian tectonic province at???1.9?Ga, including the Salma eclogite association, was caused by the enormous crustal heating that spread from the Lapland granulite belt southward. Radiogenic 176Hf enrichment of 1.9?Ga zircon indicates recrystallization of a long-existed garnet with release of significant amount of 176Hf.
DS202006-0938
2020
Mitchell, R.H.Potassic alkaline rocks: leucitites, lamproites, and kimberlites.Encyclopedia of Geology, 2nd edition 25p. PdfGlobalalkaline rocks - review

Abstract: This article describes leucitites, lamproites, and kimberlites, rock types which are enriched in potassium and depleted in aluminum relative to common rocks such as granite, andesite or basalt. Although these rocks relatively rare, some varieties have considerable economic significance as they are the only primary sources of diamond. The petrographic and mineralogical data required for identification, characterization, and classification of these rock types are described together with aspects of their isotope geochemistry that permit recognition of the sources of their parental magmas in the lithospheric and/or asthenospheric mantle of the Earth. Leucitites are considered to be members of a suite of plagioclase-bearing potassic volcanic rocks (leucite phonolites and tephrites) associated with recent subduction processes at continental margins; they never contain diamonds. Lamproites comprise a petrological clan of rocks ranging widely in their mineralogy, texture, and composition. Members of this clan range from ultrabasic olivine lamproites through phlogopite-rich lamproites to relatively silica-rich diopside leucite lamproites. Lamproites occur as lavas, pyroclastic, and hypabyssal rocks and have eruption styles similar to basaltic volcanism. Kimberlites are a group of volatile-rich ultrabasic silica-undersaturated rocks known principally from hypabyssal, and pyroclastic subvolcanic environments. The latter form three types of vent systems: subaerial Fort a la Corne pyroclastic deposits; Kimberley-type intrusive pyroclastic diatremes or pipes; and Lac de Gras pyroclastic volcanic/pyroclastic vents. Both kimberlites and lamproites are emplaced in continental cratons and marginal accreted mobile belts, although only those emplaced in cratons are diamond-bearing. Kimberlites are considered to be derived from asthenospheric mantle, whereas lamproites originate from metamorphosed and metasomatized subducted material at the lithosphere-asthenosphere boundary. Lamproites are divided into cratonic and orogenic varieties depending on whether the subduction was ancient or recent in age.
DS202011-2052
2020
Mitchell, R.H.Igneous Rock Associations 26. Lamproites, exotic potassic alkaline rocks: a review of nomenclature, characterization and origins.Geoscience Canada OPEN ACCESS, Vol. 47, pp. 119-143. Globallamproites

Abstract: Lamproite is a rare ultrapotassic alkaline rock of petrological importance as it is considered to be derived from metasomatized lithospheric mantle, and of economic significance, being the host of major diamond deposits. A review of the nomenclature of lamproite results in the recommendation that members of the lamproite petrological clan be named using mineralogical-genetic classifications to distinguish them from other genetically unrelated potassic alkaline rocks, kimberlite, and diverse lamprophyres. The names “Group 2 kimberlite” and “orangeite” must be abandoned as these rock types are varieties of bona fide lamproite restricted to the Kaapvaal Craton. Lamproites exhibit extreme diversity in their mineralogy which ranges from olivine phlogopite lamproite, through phlogopite leucite lamproite and potassic titanian richterite-diopside lamproite, to leucite sanidine lamproite. Diamondiferous olivine lamproites are hybrid rocks extensively contaminated by mantle-derived xenocrystic olivine. Currently, lamproites are divided into cratonic (e.g. Leucite Hills, USA; Baifen, China) and orogenic (Mediterranean) varieties (e.g. Murcia-Almeria, Spain; Afyon, Turkey; Xungba, Tibet). Each cratonic and orogenic lamproite province differs significantly in tectonic setting and Sr-Nd-Pb-Hf isotopic compositions. Isotopic compositions indicate derivation from enriched mantle sources, having long-term low Sm/Nd and high Rb/Sr ratios, relative to bulk earth and depleted asthenospheric mantle. All lamproites are considered, on the basis of their geochemistry, to be derived from ancient mineralogically complex K-Ti-Ba-REE-rich veins, or metasomes, in the lithospheric mantle with, or without, subsequent contributions from recent asthenospheric or subducted components at the time of genesis. Lamproite primary magmas are considered to be relatively silica-rich (~50-60 wt.% SiO2), MgO-poor (3-12 wt.%), and ultrapotassic (~8-12 wt.% K2O) as exemplified by hyalo-phlogopite lamproites from the Leucite Hills (Wyoming) or Smoky Butte (Montana). Brief descriptions are given of the most important phreatomagmatic diamondiferous lamproite vents. The tectonic processes which lead to partial melting of metasomes, and/or initiation of magmatism, are described for examples of cratonic and orogenic lamproites. As each lamproite province differs with respect to its mineralogy, geochemical evolution, and tectonic setting there is no simple or common petrogenetic model for their genesis. Each province must be considered as the unique expression of the times and vagaries of ancient mantle metasomatism, coupled with diverse and complex partial melting processes, together with mixing of younger asthenospheric and lithospheric material, and, in the case of many orogenic lamproites, with Paleogene to Recent subducted material.
DS202003-0351
2020
Mohiuddin, A., Karato, S., Girard, J.Slab weakening during olivine to ringwoodite transition in the mantle.Nature Geoscience, Vol. 13, pp. 170-174.Mantleolivine

Abstract: The strength of subducted slabs in the mantle transition zone influences the style of mantle convection. Intense deformation is observed particularly in relatively old subducted slabs in the deep mantle transition zone. Understanding the cause of this regional and depth variation in slab deformation requires constraint of the rheological properties of deep mantle materials. Here, we report results of in situ deformation experiments during the olivine to ringwoodite phase transformation, from which we infer the deformation process under the conditions of cold slabs deep in the mantle transition zone. We find that newly transformed fine-grained ringwoodite deforms by diffusion creep and that its strength is substantially smaller than that of coarser-grained minerals but increases with time. Scaling analysis, based on a model of transformation kinetics and grain-size evolution during a phase transformation, suggests that a cold slab will be made of a mixture of weak, fine-grained and strong, coarse-grained materials in the deep transition zone, whereas a warm slab remains strong because of its large grain size. We propose that this temperature dependence of grain size may explain extensive deformation of cold slabs in the deep transition zone but limited deformation of relatively warm slabs.
DS202002-0208
2020
Mohiuddin, A., Karto, S-i., Girard, J.Slab weakening during the olivine to ringwoodite transition in the mantle.Nature Geoscience, doi: 10.1038/s41561-019-0523Mantlesubduction

Abstract: The strength of subducted slabs in the mantle transition zone influences the style of mantle convection. Intense deformation is observed particularly in relatively old subducted slabs in the deep mantle transition zone. Understanding the cause of this regional and depth variation in slab deformation requires constraint of the rheological properties of deep mantle materials. Here, we report results of in situ deformation experiments during the olivine to ringwoodite phase transformation, from which we infer the deformation process under the conditions of cold slabs deep in the mantle transition zone. We find that newly transformed fine-grained ringwoodite deforms by diffusion creep and that its strength is substantially smaller than that of coarser-grained minerals but increases with time. Scaling analysis, based on a model of transformation kinetics and grain-size evolution during a phase transformation, suggests that a cold slab will be made of a mixture of weak, fine-grained and strong, coarse-grained materials in the deep transition zone, whereas a warm slab remains strong because of its large grain size. We propose that this temperature dependence of grain size may explain extensive deformation of cold slabs in the deep transition zone but limited deformation of relatively warm slabs.
DS202001-0028
2019
Moilanen, J., Pavlov, B., Karshakov, E., Volovitsky, A., Garakoev. A.Airborne geophysical technologies as a basis for diamond field prognoses in regional and state scale.2019 Twelth International Conference Oct 1-3. Moscow, IEEE DOI 11.09/MLSD .2019.8911014Africa, Angola, Russia, Yakutiageophysics

Abstract: We show how to increase the effectiveness of the prognoses of kimberlite bodies by using airborne geophysical technologies. We show the advantages of electromagnetic and magnetic methods for predicting kimberlite pipes. You will see examples of a regional diamond survey in Angola and Siberia.
DS202009-1641
2020
Moine, B.N., Bolfan-Casanova, N., Radu, I.B., Ionov, D.A., Costin, G., Korsakov, A.V., Golovin, A.V., Oleinikov, O.B., Deloule, E., Cottin, J.Y.Molecular hydrogen in minerals as a clue to interpret deltaD variations in the mantle. ( Omphacites from eclogites from Kaapvaal and Siberian cratons.)Nature Communications, doi:.org/10.1038/ s41467-020-17442 -8 11p. PdfAfrica, South Africa, Russia, Siberiawater

Abstract: Trace amounts of water dissolved in minerals affect density, viscosity and melting behaviour of the Earth’s mantle and play an important role in global tectonics, magmatism and volatile cycle. Water concentrations and the ratios of hydrogen isotopes in the mantle give insight into these processes, as well as into the origin of terrestrial water. Here we show the presence of molecular H2 in minerals (omphacites) from eclogites from the Kaapvaal and Siberian cratons. These omphacites contain both high amounts of H2 (70 to 460 wt. ppm) and OH. Furthermore, their ?D values increase with dehydration, suggesting a positive H isotope fractionation factor between minerals and H2-bearing fluid, contrary to what is expected in case of isotopic exchange between minerals and H2O-fluids. The possibility of incorporation of large quantities of H as H2 in nominally anhydrous minerals implies that the storage capacity of H in the mantle may have been underestimated, and sheds new light on H isotope variations in mantle magmas and minerals.
DS202002-0209
2019
Molnar, P.Lower mantle dynamics perceived with 50 years of hindsight from plate tectonics.Geochemistry, Geophysics, Geosystems, Vol. 20, 12, pp. 5619-5649.( open access)Mantleplate tectonics

Abstract: Fifty years ago, plate tectonics united many aspects of the surface geology of the Earth, but little connection to the lower mantle was seen. Today, most view plate tectonics as the relative movements of cold, top, stiff boundary layers of a convecting system that reaches to the core?mantle boundary and with aspects of the deep structure not foreseen decades ago. Large provinces in the deepest ~1,000 km, in which P and S wave speeds are relatively low, not only seem to be chemically different from the neighboring mantle and from that at shallower depths, but their distribution also correlates with some aspects of the overlying surface geology, including the positions of major plumes rising from deep in the mantle and the positions of continents 100 to 200 Ma. These correlations imply a geodynamic connection between the lower mantle and the crust. Scaling laws derived from experiments in geophysical fluid mechanics suggest that the chemically distinct provinces may be relics from the earliest formation of the earth, but if not, they nevertheless have evolved slowly on the timescales of geologic eras. A concurrent emerging view of the lower mantle, however, also places increased emphasis on a boundary at ~1,000 (±100) km depth, and this boundary might define a barrier to cold sinking slabs of lithosphere. A few isolated plumes of hot material that are also chemically different from most of the mantle penetrate this interface at 1,000 km, but it seems possible that this boundary may separate mantle convection into two separate layers, as was thought 50 years ago in the early plate tectonics era, when the 660?km discontinuity was thought to separate two independently convecting layers. If convection is better described as layered than involving the entire mantle as one layer, the old view of the driving mechanism of plate tectonics—that high lithostatic pressures at ridges push plates apart, cold, dense sinking slabs pull them down and drag over the asthenosphere resists plate motions—seems to be revalidated, and the relative motions of plates do not require a role for the lower mantle.
DS202008-1424
2018
Moore, A.Falconbridge discovery of the Gope ( Go25) ( Ghaghoo) kimberlite, central Kalahari, Botswana.Botswana Journal of Earth Sciences, Vol. 7, pp. 35-41. pdfAfrica, BotswanaDeposit - Gope

Abstract: The Gope (Go25) kimberlite was discovered by Falconbridge Explorations Limited (Botswana) (FELB) in 1981, following a helicopter-supported sampling programme within Reconnaissance Permits RP8/79 and RP1/80, covering approximately 78 500 km2, centred on the Central Kalahari area of Botswana (Fig. 1). The majority of this area is covered by sands of the Kalahari Group, with thicknesses up to 100m. Unfortunately, most original company files, including mineral distribution maps and mineral analyses were not available to the author. This paper draws on the excellent summary of the discovery of the Gope (Go-25) kimberlite by Lee et al. (2009), together with the author’s personal recollections.
DS202011-2053
2020
Moore, A.The evidence for a cognate origin for the majority of all kimberlitic olivines. GSSA Talk Oct 14, https://www.youtube.com/watch?v=1QCCPkShjw4Globalolivine
DS202003-0352
2020
Moore, A.,Yudovskaya, M., Prover, A., Blenkinsop, T.Evidence for olivine deformation in kimberlites and other mantle derived magmas during crustal emplacement. LemphaneContributions to Mineralogy and Petrology, Vol. 175, 9p. PdfAfrica, Lesothoolivine

Abstract: This paper highlights published and new field and petrographic observations for late-stage (crustal level) deformation associated with the emplacement of kimberlites and other mantle-derived magmas. Thus, radial and tangential joint sets in the competent 183 Ma Karoo basalt wall rocks to the 5 ha. Lemphane kimberlite blow in northern Lesotho have been ascribed to stresses linked to eruption of the kimberlite magma. Further examples of emplacement-related stresses in kimberlites are brittle fractures and close-spaced parallel shears which disrupt olivine macrocrysts. In each of these examples, there is no evidence of post-kimberlite regional tectonism which might explain these features, indicating that they reflect auto-deformation in the kimberlite during or immediately post-emplacement. On a microscopic scale, these inferred late-stage stresses are reflected by fractures and domains of undulose extinction which traverse core and margins of some euhedral and anhedral olivines in kimberlites and olivine melilitites. Undulose extinction and kink bands have also been documented in olivines in cumulates from layered igneous intrusions. Our observations thus indicate that these deformation features can form at shallow levels (crustal pressures), which is supported by experimental evidence. Undulose extinction and kink bands have previously been presented as conclusive evidence for a mantle provenance of the olivines—i.e. that they are xenocrysts. The observation that these deformation textures can form in both mantle and crustal environments implies that they do not provide reliable constraints on the provenance of the olivines. An understanding of the processes responsible for crustal deformation of kimberlites could potentially refine our understanding of kimberlite emplacement processes.
DS202010-1862
2020
Morizet, Y., Larre, C., Di Carlo, I., Gaillard, F.High S and high CO2 contents in haplokimberlite: an experimental and Raman spectroscopic study.Mineralogy and Petrology, Vol. 114, pp. 363-373. pdfMantlemelting

Abstract: Sulfur is an important element present in natural kimberlites and along with CO2, S can play a role in the kimberlite degassing. We have investigated experimentally the change in S content and CO2 solubility in synthetic kimberlitic melts in response to a range of pressure (0.5 to 2.0 GPa) and temperature (1500 to 1525 °C). Several initial S concentrations were investigated ranging from 0 to 24000 ppm. The dissolved CO2 and S were determined by Raman spectroscopy and Electron Probe Micro-Analyses. Under the investigated oxidizing conditions (?FMQ?+?1), S is dissolved in the glass only as S6+ forming sulfate molecular groups (SO42?). The measured S concentration in the glasses increases from 2900 to 22000 ppm. These results suggest that the experimental conditions were below saturation with respect to S and that the S solubility is higher than 22000 ppm for kimberlitic melts; regardless of the experimental conditions considered here. CO2 is dissolved as CO32? molecular groups. The CO2 solubility ranges from 3.0 to 11.3 wt% between 0.5 and 2.0 GPa. CO2 solubility is not affected by the presence of S; which suggests that SO42? and CO32? clusters have two distinct molecular environments not interacting together. This result implies that both CO2 and S are efficiently transported by kimberlitic melt from the upper mantle towards the atmosphere.
DS202006-0939
2020
Moulin, M., Aslainian, D., Evain, M., Lepetre, A., Schnurle, P., Verrier, F., Thompson, J., De Clarens, P., Leroy, S., Dias, N.Gondwana breakup: messages from the north Natal Valley.Terra Nova, Vol. 32, 3, pp. 205-210.Africa, Mozambiquegeophysics - seismics

Abstract: The Natal Valley, offshore Mozambique, is a key area for understanding the evolution of East Gondwana. Within the scope of the integrated multidisciplinary PAMELA project, we present new wide?angle seismic data and interpretations, which considerably alter Geoscience paradigms. These data reveal the presence of a 30?km?thick crust that we argue to be of continental nature. This falsifies all the most recent palaeo?reconstructions of the Gondwana. This 30?km?thick continental crust 1,000 m below sea level implies a complex history with probable intrusions of mantle?derived melts in the lower crust, connected to several occurrences of magmatism, which seems to evidence the crucial role of the lower continental crust in passive margin genesis.
DS202005-0750
2020
Mukhopadhyay, D., Matin, A.The architecture and evolution of the Singhbhum craton.Episodes ( IUGS), Vol. 43, 1, pp. 19-50.Indiacraton

Abstract: The Singhbhum Craton is built up by successive pulses of discrete granitic magmatism at ~3.52 Ga, ~3.47-3.43 Ga, and ~3.40-3.35 Ga that produced tonalitetrondhjemite-granodiorite (TTG)-type suites and were followed by younger pulses at 3.32-3.35 Ga, and 3.31-3.28 Ga producing voluminous granitic-granodioritic magma. There is enough evidence to indicate that continental crust building activity started in the Hadean time and continued through Eoarchean. But the rocks of this period were fully recycled to generate the Paleoarchean and younger crust. The different pulses of granitic magmatism during the Paleoarchean were interspersed with the formation of supracrustal rocks which are now preserved as supracrustal belts peripheral to the craton or as internal screens within the craton. Halfnium isotopic record suggests that the Hadean and Eoarchean granitoids were sourced in an enriched reservoir, probably some form of early mafic protocrust. From ~3.6-3.5 Ga a shift in the isotopic composition of Hf is noticed, marked by upward excursion of ?Hf(t) plots towards suprachondritic values, signifying that the early mantle reservoir was serially modified by contamination by a juvenile melt derived from a depleted source. This probably signals a change in the geodynamic scenario, major depletion of the mantle and generation of voluminous TTG melts. There are contending hypotheses of plume-driven and subduction-driven mechanisms of continental crust formation. In the Singhbhum Craton during Hadean and Eoarchean times episodic mantle plumes probably operated in a stagnant lid tectonic setting. Repeated plume activities and the formation of oceanic plateaus might have triggered the onset of subduction which at the initial stages might have been of short duration. The transition from plume-driven tectonics to subduction-driven tectonics might have taken place at about 3.5 Ga. The supracrustal belts of the Older Metamorphic Group (OMG) and the Iron Ore Group (IOG) are thought to have formed in supra-subduction settings. Widespread metamorphism and deformation affected the craton during 3.34-3.26 Ga. By 3.1 Ga the Singhbhum Craton had stabilized and emerged as a landmass. Paleosols developed on the surface; rift basins were formed which were receptacles of siliciclastic sediments and mafic volcanics; anorogenic K-feldspar bearing granites were emplaced. Swarms of mafic dykes of Paleo- to Meso-Proterozoic age intruded the craton marking a tensional regime that was probably related to the initial stage of basin formation in the North Singhbhum Mobile Belt.
DS202009-1642
2000
Mukhopadhyay, D., Matin, A.The architecture and evolution of the Singbhum craton.Episodes, Vol. 43, 1, pp. 19- 50.Indiamagmatism

Abstract: The Singhbhum Craton is built up by successive pulses of discrete granitic magmatism at ~3.52 Ga, ~3.47-3.43 Ga, and ~3.40-3.35 Ga that produced tonalitetrondhjemite-granodiorite (TTG)-type suites and were followed by younger pulses at 3.32-3.35 Ga, and 3.31-3.28 Ga producing voluminous granitic-granodioritic magma. There is enough evidence to indicate that continental crust building activity started in the Hadean time and continued through Eoarchean. But the rocks of this period were fully recycled to generate the Paleoarchean and younger crust. The different pulses of granitic magmatism during the Paleoarchean were interspersed with the formation of supracrustal rocks which are now preserved as supracrustal belts peripheral to the craton or as internal screens within the craton. Halfnium isotopic record suggests that the Hadean and Eoarchean granitoids were sourced in an enriched reservoir, probably some form of early mafic protocrust. From ~3.6-3.5 Ga a shift in the isotopic composition of Hf is noticed, marked by upward excursion of ?Hf(t) plots towards suprachondritic values, signifying that the early mantle reservoir was serially modified by contamination by a juvenile melt derived from a depleted source. This probably signals a change in the geodynamic scenario, major depletion of the mantle and generation of voluminous TTG melts. There are contending hypotheses of plume-driven and subduction-driven mechanisms of continental crust formation. In the Singhbhum Craton during Hadean and Eoarchean times episodic mantle plumes probably operated in a stagnant lid tectonic setting. Repeated plume activities and the formation of oceanic plateaus might have triggered the onset of subduction which at the initial stages might have been of short duration. The transition from plume-driven tectonics to subduction-driven tectonics might have taken place at about 3.5 Ga. The supracrustal belts of the Older Metamorphic Group (OMG) and the Iron Ore Group (IOG) are thought to have formed in supra-subduction settings. Widespread metamorphism and deformation affected the craton during 3.34-3.26 Ga. By 3.1 Ga the Singhbhum Craton had stabilized and emerged as a landmass. Paleosols developed on the surface; rift basins were formed which were receptacles of siliciclastic sediments and mafic volcanics; anorogenic K-feldspar bearing granites were emplaced. Swarms of mafic dykes of Paleo- to Meso-Proterozoic age intruded the craton marking a tensional regime that was probably related to the initial stage of basin formation in the North Singhbhum Mobile Belt.
DS202002-0210
2019
Mukhopadhyay, S., Parai, R.Noble gases: a record of Earth's evolution and mantle dynamics.Annual Review of Earth and Planetary Sciences, Vol. 47, pp. 389-417.Mantlegeodynamics

Abstract: Noble gases have played a key role in our understanding of the origin of Earth's volatiles, mantle structure, and long-term degassing of the mantle. Here we synthesize new insights into these topics gained from high-precision noble gas data. Our analysis reveals new constraints on the origin of the terrestrial atmosphere, the presence of nebular neon but chondritic krypton and xenon in the mantle, and a memory of multiple giant impacts during accretion. Furthermore, the reservoir supplying primordial noble gases to plumes appears to be distinct from the mid-ocean ridge basalt (MORB) reservoir since at least 4.45 Ga. While differences between the MORB mantle and plume mantle cannot be explained solely by recycling of atmospheric volatiles, injection and incorporation of atmospheric-derived noble gases into both mantle reservoirs occurred over Earth history. In the MORB mantle, the atmospheric-derived noble gases are observed to be heterogeneously distributed, reflecting inefficient mixing even within the vigorously convecting MORB mantle.
DS202001-0029
2019
Mulyukova, E., Bercovici, D.The generation of plate tectonics from grains to global scales: a brief review.Tectonics, doi.org10.1029/ 2018tc005447Mantleplate tectonics

Abstract: The physics of rock deformation in the lithosphere governs the formation of tectonic plates, which are characterized by strong, broad plate interiors, separated by weak, localized plate boundaries. The size of mineral grains in particular controls rock strength and grain reduction can lead to shear localization and weakening in the strong ductile portion of the lithosphere. Grain damage theory describes the competition between grain growth and grain size reduction as a result of deformation, and the effect of grain size evolution on the rheology of lithospheric rocks. The self?weakening feedback predicted by grain damage theory can explain the formation of mylonites, typically found in deep ductile lithospheric shear zones, which are characteristic of localized tectonic plate boundaries. The amplification of damage is most effective when minerallic phases, like olivine and pyroxene, are well mixed on the grain scale. Grain mixing theory predicts two coexisting deformation states of unmixed materials undergoing slow strain rate, and well?mixed materials with large strain rate; this is in agreement with recent laboratory experiments, and is analogous to Earth's plate?like state. A new theory for the role of dislocations in grain size evolution resolves the rapid timescale of dynamic recrystallization. In particular, a toy model for the competition between normal grain growth and dynamic recrystallization predicts oscillations in grain size with periods comparable to earthquake cycles and postseismic recovery, thus connecting plate boundary formation processes to the human timescale.
DS202007-1165
2020
Munch, F.D., Grayver, A.V., Guzavina, M., Kuvshinov, A.V., Khan, A.Joint inversion of daily and long period geomagnetic transfer functions reveals lateral variations in mantle water content.Journal of Geophysical Letters, Vol. 47, e2020GL087222Mantlewater

Abstract: The amount of water trapped in the Earth's interior has a strong effect on the evolution and dynamics of the planet, which ultimately controls the occurrence of earthquakes and volcanic eruptions. However, the distribution of water inside the Earth is not yet well understood. To study the Earth's deep interior, we make use of changes in the Earth's magnetic field to detect variations in electrical conductivity inside the planet. Electrical conductivity is a characteristic of a rock that varies with temperature and water content. Here, we present a novel methodology to estimate the amount of water in different regions of Earth's mantle. Our analysis suggests the presence of small amounts of water in the mantle underneath Europe, whereas larger amounts are expected beneath North America and northern Asia.
DS202005-0751
2020
Munch, F.D., Khan, A., Tauzin, B., vn Driel, M., Giardini, D.Seismological evidence for thermo-chemical heterogeneity in Earth's continental mantle.Earth and Planetary Science Letters, Vol. 539, 116240 9p. PdfMantlegeophysics - seismics

Abstract: Earth's thermo-chemical structure exerts a fundamental control on mantle convection, plate tectonics, and surface volcanism. There are indications that mantle convection occurs as an intermittent-stage process between layered and whole mantle convection in interaction with a compositional stratification at 660 km depth. However, the presence and possible role of any compositional layering in the mantle remains to be ascertained and understood. By interfacing inversion of a novel global seismic data set with petrologic phase equilibrium calculations, we show that a compositional boundary is not required to explain short- and long-period seismic data sensitive to the upper mantle and transition zone beneath stable continental regions; yet, radial enrichment in basaltic material reproduces part of the complexity present in the data recorded near subduction zones and volcanically active regions. Our findings further indicate that: 1) cratonic regions are characterized by low mantle potential temperatures and significant lateral variability in mantle composition; and 2) chemical equilibration seems more difficult to achieve beneath stable cratonic regions. These findings suggest that the lithologic integrity of the subducted basalt and harzburgite may be better preserved for geologically significant times underneath cratonic regions.
DS202010-1863
2020
Murphy, K.P., Johnson, A.B.Sailing the sea of open access: celestial navigation or dead reckoning?Mineralogical Magazine, Vol. 84, pp. 495-501. pdfGlobalhistory

Abstract: The Open Access movement has gathered significant momentum over the last couple of years. This has been instigated largely by cOAlition S and those funders which support its aims. Is ‘Read and Publish’ the way forward? Will it work for all publishers? All authors? All subscribers? All readers? This article looks at the history of OA and updates a similar piece from 2013. A detailed glossary of terms is given at the end of the article.
DS202011-2054
2020
Murri, M., Smith, R.L., McColl, K., Hart, M., Alvaro, M., Jones, A.P., Nemeth, P., Salzmann, C.G., Cora, F., Domeneghetti, M.C., Nestola, F., Sobolev, N.V., Vishnevsky, S.A., Logvinova, A.M., McMillan, P.F.Quantifying hexagonal stacking in diamond.Nature/scientific reports, 8p. PdfGlobalcrystallography

Abstract: Diamond is a material of immense technological importance and an ancient signifier for wealth and societal status. In geology, diamond forms as part of the deep carbon cycle and typically displays a highly ordered cubic crystal structure. Impact diamonds, however, often exhibit structural disorder in the form of complex combinations of cubic and hexagonal stacking motifs. The structural characterization of such diamonds remains a challenge. Here, impact diamonds from the Popigai crater were characterized with a range of techniques. Using the MCDIFFaX approach for analysing X-ray diffraction data, hexagonality indices up to 40% were found. The effects of increasing amounts of hexagonal stacking on the Raman spectra of diamond were investigated computationally and found to be in excellent agreement with trends in the experimental spectra. Electron microscopy revealed nanoscale twinning within the cubic diamond structure. Our analyses lead us to propose a systematic protocol for assigning specific hexagonality attributes to the mineral designated as lonsdaleite among natural and synthetic samples.
DS202008-1425
2019
Musenwa, L., Khumalo, T., Kgaphola, M., Masemola, S., van Wyk, G.The new Cullinan AG milling circuit - a narrative of progress.The Journal of the Southern African Insitute of Mining and Metallurgy, Vol. 119, Feb. 10p. PdfAfrica, South Africadeposit - Cullinan

Abstract: In 2017, Petra Diamonds completed the construction and commissioning of a modern, fit-for-purpose diamond processing plant at Cullinan Diamond Mine (CDM). The design of CDM's milling circuit is unconventional in that it comprises an autogenous (AG) mill with a grate discharge with large ports, low-revolution jaw crushers, and high-pressure grinding roll crushers with large operating gaps. In this paper we review the design to provide guidance on what is expected from the milling circuit and to demonstrate how the design aims to address challenges experienced in the old plant, which was based on staged crushing technology. We assessed the performance of the CDM AG milling circuit from commissioning and early production stages to examine its impact along multiple dimensions. In the assessment we sought to understand the lessons from our milling circuit regarding diamond liberation, energy consumption, and the future of diamond processing as a whole.
DS202006-0940
2020
Nabyl, Z., Massuyeau, M., Gaillard, F., Tuduri, J., Iacono-Marziano, G., Rogerie, G., Le Trong, E., Di Carlo, I., Melleton, J., Bailly, L.A window in the course of alkaline magma differentiation conducive to immiscible REE-rich carbonatites.Geochimica et Cosmochimica Acta, in press available 57p. PdfMantlecarbonatite

Abstract: Rare earth element (REE) enrichments in carbonatites are often described as resulting from late magmatic-hydrothermal or supergene processes. However, magmatic pre-enrichment linked to the igneous processes at the origin of carbonatites are likely to contribute to the REE fertilisation. Experimental constraints reveals that immiscibility processes between carbonate and silicate melts can lead to both REE enrichments and depletions in carbonatites making the magmatic processes controlling REE enrichments unclear. We link REE contents of carbonatites to the magmatic stage at which carbonatites are separated from silicate magma in their course of differentiation. We present results of experiments made at pressure and temperature conditions of alkaline magmas and associated carbonatites differentiation (0.2-1.5 GPa; 725-975?°C; FMQ to FMQ?+?2.5), simultaneously addressing crystal fractionation of alkaline magmas and immiscibility between carbonate (calcio-carbonate type) and silicate melts (nephelinite to phonolite type). The experimental data shows that the degree of differentiation, controlling the chemical composition of alkaline melts, is a key factor ruling the REE concentration of the coexisting immiscible carbonate melts. In order to predict carbonate melt REE enrichments during alkaline magma differentiation, we performed a parameterisation of experimental data on immiscible silicate and carbonate melts, based exclusively on the silica content, the alumina saturation index and the alkali/alkaline-earth elements ratio of silicate melts. This parameterisation is applied to more than 1600 geochemical data of silicate magmas from various alkaline provinces (East African Rift, Canary and Cape Verde Islands) and show that REE concentrations of their potential coeval carbonatite melts can reach concentration ranges similar to those of highly REE enriched carbonatites (?REE?>?30 000?ppm) by immiscibility with phonolitic/phono-trachytic melt compositions, while more primitive alkaline magmas can only be immiscible with carbonatites that are not significantly enriched in REE.
DS202009-1643
2020
Nabyl, Z., Massuyeau, M.,Gaillard, F., Tuduri, J., Gregory, G-M., Trong, E., Di Carlo, I., Melleton, J., Bailly, L. A window in the course of alkaline magma differentiation conducive to immiscible REE-rich carbonatite.Geochimica et Cosmochimica Acta, Vol. 282, pp. 297-323.Africa, East Africacarbonatites

Abstract: Rare earth element (REE) enrichments in carbonatites are often described as resulting from late magmatic-hydrothermal or supergene processes. However, magmatic pre-enrichment linked to the igneous processes at the origin of carbonatites are likely to contribute to the REE fertilisation. Experimental constraints reveals that immiscibility processes between carbonate and silicate melts can lead to both REE enrichments and depletions in carbonatites making the magmatic processes controlling REE enrichments unclear. We link REE contents of carbonatites to the magmatic stage at which carbonatites are separated from silicate magma in their course of differentiation. We present results of experiments made at pressure and temperature conditions of alkaline magmas and associated carbonatites differentiation (0.2-1.5 GPa; 725-975?°C; FMQ to FMQ?+?2.5), simultaneously addressing crystal fractionation of alkaline magmas and immiscibility between carbonate (calcio-carbonate type) and silicate melts (nephelinite to phonolite type). The experimental data shows that the degree of differentiation, controlling the chemical composition of alkaline melts, is a key factor ruling the REE concentration of the coexisting immiscible carbonate melts. In order to predict carbonate melt REE enrichments during alkaline magma differentiation, we performed a parameterisation of experimental data on immiscible silicate and carbonate melts, based exclusively on the silica content, the alumina saturation index and the alkali/alkaline-earth elements ratio of silicate melts. This parameterisation is applied to more than 1600 geochemical data of silicate magmas from various alkaline provinces (East African Rift, Canary and Cape Verde Islands) and show that REE concentrations of their potential coeval carbonatite melts can reach concentration ranges similar to those of highly REE enriched carbonatites (?REE?>?30 000?ppm) by immiscibility with phonolitic/phono-trachytic melt compositions, while more primitive alkaline magmas can only be immiscible with carbonatites that are not significantly enriched in REE.
DS202002-0211
2020
Nadolly, V.A., Shatsky, V.S., Yuryeva, O.P., Rakhmanova, M.I., Komarovskikh, A.Yu., Kalinin, A.A., Palyanov, Yu.N.Formation features of N3V centers in diamonds from the Kholomolokh placer in the Northeast Siberian craton.Physics and Chemistry of Minerals, Vol. 47, 4, 7p. PdfRussia, Siberiadeposit - Khololmolokh

Abstract: In recent years, despite significant progress in the development of new methods for the synthesis of diamond crystals and in their post-growth treatment, many questions remain unclear about the conditions for the formation and degradation of aggregate impurity nitrogen forms. Meanwhile, they are very important for understanding (evaluating) the origin, age, and post-growth conditions of natural diamonds. In the present work, an attempt was made to analyze the causes of the formation of high concentrations of N3V centers in natural IaB-type diamonds from the Kholomolokh placer (the Northeast Siberian craton). The possibility of decay of B centers during the plastic deformation of diamonds is analyzed and experiments on the high-temperature annealing of diamonds containing B centers are reported. The formation of N3V centers during the destruction of the B centers at high-pressure annealing of crystals has been established by experiment. It is assumed that, in the post-growth period, diamond crystals were exposed to tectono-thermal stages of raising the superplumes of the Earth's crust of the Siberian craton.
DS202009-1644
2019
Naipal, R., Kroonenberg, S.B., Mason, P.R.D.Ultramafic rocks of the Paleoproterozoic greenstone belt in the Guiana shield of Suriname, and their mineral potential.SAXI-XI Inter Guiana Geological Conference, held Paramaribo, Suriname., 5p. PdfSouth America, Surinamediamond

Abstract: The ultramafic rocks of the Marowijne Greenstone Belt in Suriname and elsewhere in the Guiana Shield comprise both intrusive dunite-gabbroic bodies and ultramafic lavas and volcaniclastic rocks. They were emplaced in the early stages of the Trans-Amazonian Orogeny (2.26-2.09 Ga), but their petrogenesis and geotectonic significance have still to be elaborated. They present several economically interesting mineralisations, including chromium, nickel, platinum, gold and diamonds. In Suriname diamonds are found since the 19 th century; possible source rocks show similarities with the diamondiferous komatiitic volcaniclastic rocks in Dachine, French Guiana and in Akwatia in the Birimian Greenstone Belt of Ghana. This might point to a regionally extensive diamond belt in the Guiana Shield and its predrift counterpart in the West-African Craton.
DS202009-1645
2020
Naipal, R., Zwaan, J.C.(Hanco),, Kroonenberg, S.B., Kreigsman, L.M., Mason, P.R.D.Diamonds from the Nassau Mountains, Suriname.Journal of Gemmology, Vol. 37, 2, pp. 180-191. pdfSouth America, Surinamedeposit - Paramaka Creek

Abstract: Alluvial diamonds have been found in Suriname since the late 19th century, but to date the details of their origin remain unclear. Here we describe diamonds from Paramaka Creek (Nassau Mountains area) in the Marowijne greenstone belt, Guiana Shield, north-eastern Suriname. Thirteen samples were studied, consisting mainly of euhedral crystals with dominant octahedral and dodecahe-dral habits. They had colourless to brown to slightly greenish body colours, and some showed green or (less commonly) brown irradiation spots. Surface features showed evidence of late-stage resorption that occurred during their transport to the earth’s surface. The studied diamonds were predominantly type IaAB, with nitrogen as both A and B aggregates. In the DiamondView most samples displayed blue and/or green luminescence and concentric growth patterns. Their mineral inclusion assemblages (forsterite and enstatite) indicate a peridotitic (possibly harzburgitic) paragenesis.
DS202001-0030
2019
Najih, A., Montero, P., Verati, C., Chabou, M.C., Fekkak, A., Baidder, L., Ezzouhairi, H., Bea, F., Michard, A.Initial Pangean rifting north of the West African craton: insights from late Permian U-Pb and 40Ar/39Ar dating of alkaline magmatism from the eastern Anti-Atlas ( Morocco).Journal of Geodynamics, Vol. 132, 17p.Africa, Moroccocamptonites

Abstract: Numerous mafic dykes, sills and laccoliths crop out in the southern part of the Tafilalt basin (Eastern Anti-Atlas, Morocco). These rocks intrude the mildly folded Ordovician to Early Carboniferous formations, consisting mainly of lamprophyric dolerites and camptonites with minor gabbros and syenodiorites. Previous geochemical studies have shown that the Tafilalt magmatism of sodic-alkaline affinity has been produced by low degrees of partial melting from an enriched deep mantle source within the garnet stability field. However, the age and the geodynamic context of these rocks were presently unknown since no isotopic dating had so far been made of the Tafilalt dolerites. To resolve this issue, we present here the first 40Ar/39Ar biotite and U-Pb zircon dating from the Tafilalt alkaline magmatism. Three samples (biotite separates) yielded well-defined 40Ar/39Ar plateau ages of 264.2?±?2.7 Ma, 259.0?±?6.3 Ma and 262.6?±?4.5 Ma whereas 206Pb/238U dating of zircon from one of these samples yielded an age of 255?±?3 Ma. These ages coincide within the dating error, and indicate that this magmatism occurred in the late Permian. Considering geochronological and geochemical data, we propose that the Tafilalt magmatism reflects an early-rift magmatic activity that preceded the Triassic rifting heralded by the Central Atlantic Magmatic Province. This magmatic activity is recorded in both sides of the future Atlantic Ocean by small-volume alkaline magmatism that started in the late Permian and extends into the Triassic. The alkaline magmas are probably generated in response to an increase in the mantle potential temperature underneath the Pangea supercontinent.
DS202011-2055
2020
Nakagawa, T.A coupled core-mantle evolution: review and future prospects.Progress in Earth and Planetary Science, doi.org./10.1186/ s40645-020-00374-8 17p. PdfMantlegeophysics, geothermometry

Abstract: In this review, I provide the current status and future prospects for the coupled core-mantle evolution and specifically summarize the constraints arising from geomagnetism and paleomagnetism on the long-term secular variations of the geomagnetic field. The heat flow across the core-mantle boundary (CMB) is essential for determining the best-fit scenario that explains the observational data of geomagnetic secular variations (e.g., onset timing of the inner core growth, geomagnetic polarity reversals, and westward drift) and should include the various origins of the heterogeneous structures in the deep mantle that have affected the heat transfer across the core-mantle boundary for billions of years. The coupled core-mantle evolution model can potentially explain the onset timing of the inner core and its influence on the long-term geomagnetic secular variations, but it is still controversial among modeling approaches on the core energetics because the paleomagnetic data contains various uncertainties. Additionally, with the coupled core-mantle evolution model in geodynamo simulations, the frequency of the geomagnetic polarity reversals can be explained with the time variations of the heat flow across the CMB. Additionally, the effects of the stable region in the outermost outer core to the magnetic evolution are also crucial but there would be still uncertain for their feasibility. However, despite this progress in understanding the observational data for geomagnetic secular variations, there are several unresolved issues that should be addressed in future investigations: (1) initial conditions—starting with the solidification of the global magma ocean with the onset timing of plate tectonics and geodynamo actions and (2) planetary habitability—how the dynamics of the Earth’s deep interior affects the long-term surface environment change that has been maintained in the Earth’s multisphere coupled system.
DS202002-0212
2019
Nakagawa, T., Nakakuki, T.Dynamics in the uppermost lower mantle: insights into the deep mantle water cycle based on the numerical modeling of subducted slabs and global scale mantle dynamics.Annual Review of Earth and Planetary Sciences, Vol. 47, pp. 41-66.Mantlesubduction, water

Abstract: In this review, we address the current status of numerical modeling of the mantle transition zone and uppermost lower mantle, focusing on the hydration mechanism in these areas. The main points are as follows: (a) Slab stagnation and penetration may play significant roles in transporting the water in the whole mantle, and (b) a huge amount of water could be absorbed into the deep mantle to preserve the surface seawater over the geologic timescale. However, for further understanding of water circulation in the deep planetary interior, more mineral physics investigations are required to reveal the mechanism of water absorption in the lower mantle and thermochemical interaction across the core-mantle boundary region, which can provide information on material properties to the geodynamics community. Moreover, future investigations should focus on determining the amount of water in the early planetary interior, as suggested by the planetary formation theory of rocky planets. Moreover, the supplying mechanism of water during planetary formation and its evolution caused by plate tectonics are still essential issues because, in geodynamics modeling, a huge amount of water seems to be required to preserve the surface seawater in the present day and to not be dependent on an initial amount of water in Earth's system.
DS202005-0752
2019
Nakagawa, T., Nakakuki, T.Dynamics in the uppermost lower mantle: insights into the deep mantle water cycle based on the numerical modeling of subducted slabs and global-scale mantle dynamics.Annual Review of Earth and Planetary Sciences, Vol. 47, pp. 41-66. pdfMantlewater, subduction

Abstract: In this review, we address the current status of numerical modeling of the mantle transition zone and uppermost lower mantle, focusing on the hydration mechanism in these areas. The main points are as follows: (a) Slab stagnation and penetration may play significant roles in transporting the water in the whole mantle, and (b) a huge amount of water could be absorbed into the deep mantle to preserve the surface seawater over the geologic timescale. However, for further understanding of water circulation in the deep planetary interior, more mineral physics investigations are required to reveal the mechanism of water absorption in the lower mantle and thermochemical interaction across the core-mantle boundary region, which can provide information on material properties to the geodynamics community. Moreover, future investigations should focus on determining the amount of water in the early planetary interior, as suggested by the planetary formation theory of rocky planets. Moreover, the supplying mechanism of water during planetary formation and its evolution caused by plate tectonics are still essential issues because, in geodynamics modeling, a huge amount of water seems to be required to preserve the surface seawater in the present day and to not be dependent on an initial amount of water in Earth's system. 1) Slab stagnation and penetration of the hydrous lithosphere are essential for understanding the global-scale material circulation. 2) Thermal feedback caused by water-dependent viscosity is a main driving mechanism of water absorption in the mantle transition zone and uppermost lower mantle. 3) The hydrous state in the early rocky planets remains to be determined from cosmo- and geochemistry and planetary formation theory. 4) Volatile cycles in the deep planetary interior may affect the evolution of the surface environment.
DS202012-2235
2020
Narvekar, P., Even Zolar, C.The 2019 pipeline Prelude to the storm. Also 1p. GraphIdexonline.com, 12p. Pdf, 1p. PdfGlobaldiamond pipeline

Abstract: The 2019-2020 period is evolving as a dramatic game changer for the entire world. This is even more so for the diamond industry where a gradual pipeline restructuring process finally matured into an inevitable and, in fact, a most desirable conclusion for the midstream sector - the manufacturers of the rough and the traders of the polished. Finally, this quite squeezed sector from a profitability aspect, began to act purely in their own economic, financial, and commercial self-interest less burdened by producer pressures to “relieve” them of their stocks. Led by the massive Indian diamond sector, the manufacturers put four months break on their rough diamond purchases. In 2019 the producers were faced with considerable resistance to purchase their rough allocation which was met, to quote the CEO of De Beers, with unprecedented flexibility in the way it sold its diamonds to sightholders because of the nature of the market”. In February 2020, well before the pandemic struck the world in full force, the heads of both De Beers and Anglo American announced that they would change their allocation system (sights) and that no buyer will be "unaffected" by the changes in the sight system. The Indian industry didn’t wait to find out what scheme the producer would introduce.
DS202001-0031
2019
Nascimento, M.A., Correia Rio, D., Lopes dos Santos, I.P., Conceicao, H.Mangoan ilmenite and implications for diamond bearing kimberlites: a case study at the Aroeira kimberlitic dyke, Nordestina kimberlitic Province, Bahia. ( abstract only in english) ***PORTwww.annuario.igeo .ufrj.br ( researchgate.com), 15p. Pdf.South America, Brazil, Bahiadeposit - Aroeira
DS202006-0941
2020
Nasdala, L., Schmidt, C.Applications of raman spectroscopy in mineralogy and geochemistry.Elements, Vol. 16, pp. 99-104.Africa, South Africadeposit - Finsch

Abstract: The application of Raman spectroscopy for the identification and characterization of minerals and related materials has increased appreciably during recent years. Raman spectroscopy has proven to be a most valuable and versatile analytical tool. Successful applications cover virtually all the mineralogical sub-disciplines, and have become more numerous in geochemistry. We present a general summary of present applications, illustrated by selected examples. In addition, we briefly point out several aspects of spectral acquisition, data reduction, and interpretation of Raman results that are important for the application of Raman spectroscopy as a reliable analytical tool.
DS202011-2056
2020
Nemeth, P., McColl, K., Garvie, L.A.J., Salzmann, C.Complex nanostructures in diamond. Nature Materials, doi:10.1038/s4 1563-020-0759-8 7p. PdfGlobalmeteorites, synthetics

Abstract: Meteoritic diamonds and synthesized diamond-related materials contain a wide variety of complex nanostructures. This Comment highlights and classifies this structural complexity by a systematic hierarchical approach, and discusses the perspectives on nanostructure and properties engineering of diamond-related materials.
DS202005-0753
2020
Nestola, F.The role of elastic anisotrophy in determining the depth of formation for diamonds and their inclusions.Rendiconti Lincei. Scienze Fisiche e Naturali *** in Eng., doi.org/10.1007/ s12210-020-00897-8 9p. PdfMantlegeothermometry

Abstract: Natural diamonds and their mineral inclusions represent the deepest regions of our planet. Diamonds form between about 120/130 km in the upper mantle and possibly up to 1000 km depth in the lower mantle, and they can transport mineral inclusions, which are fragments directly from regions that are inaccessible to geologists. Diamond-inclusion system is a very precious geological object not only due to the depth of provenance in the mantle but also because of the diamond age, which ranges between 3.6 and 0.09 Ga providing information over a very wide evolution time of the Earth. It is evident that the determination of the depth of formation of the diamond-inclusion system is one of the crucial aspects to retrieve fundamental geological information about the deep mantle. However, the determination of such depth is not trivial at all and different approaches could be adopted; one of the most promising is represented by the so-called "elastic geobarometry". In this review, I will focus on elastic geobarometry and on the role that anisotropy has on the determination of the depth of diamond formation. The work will also provide a short overview of the most common approaches used to retrieve the depth of diamond formation.
DS202004-0528
2019
Nestola, F., Pasqualetto, L., Wang, W.The new nickel sulfide mineral crowningshieldite found within a superdeep diamond from Letseng.GSA Annual Meeting Phoenix, 1p. AbstractAfrica, LesothoDeposit - Letseng

Abstract: By virtue of their exceptionally deep origin and unique geological histories, diamonds have been found to contain a variety of minerals that are otherwise rare or absent at Earth’s surface. During examination of a type IIa diamond sample from the Letseng mine, Lesotho, a new nickel sulfide mineral was found as part of a fine-grained multiphase inclusion. This nickel sulfide is the natural analogue of the synthetic nickel monosulfide known as ?-NiS, with a NiAs-type structure. This new mineral has been named crowningshieldite, after G.R. Crowningshield (1919 - 2006), whose many years of innovation at the Gemological Institute of America produced countless advances in the understanding and identification of natural, treated and synthetic diamonds and other gem materials. Crowningshieldite is the high-temperature polymorph of millerite, with an inversion temperature of 379 °C from previous experiments on pure NiS. The observed sample of crowningshieldite has an empirical formula of (Ni0.90Fe0.10)S. The host diamond is gemmy, colorless, and relatively pure (type IIa, containing less than ~5 ppm nitrogen). It belongs to a variety of sublithospheric/superdeep diamonds named CLIPPIR diamonds that are notable for their metallic Fe-Ni-C-S melt inclusions. In this case, the inclusion is interpreted to be an alteration assemblage produced when a primary metallic Fe-Ni-C-S inclusion with a surface-reaching fracture reacted with hot fluids, likely associated with kimberlite emplacement. Other phases identified in association with crowningshieldite in this fine-grained alteration assemblage are magnetite-magnesioferrite, hematite, and graphite. Unexposed inclusions within the same diamond are of original, unaltered Fe-Ni-C-S composition. The new mineral crowningshieldite is a good example of the complexity and breadth of geological processes recorded within diamonds and their inclusions.
DS202012-2236
2020
Neto, J.M.M., Lafon, J-M.Crustal growth and reworking of Archean crust within the Rhyacian domains of the southeastern Guiana Shield, Brazi: evidence from zircon U-Pb-Hf and whole rock Sm-Nd geochronology.Journal of South American Earth Sciences, Vol. 103, 102740 29p pdfSouth America, Brazilcraton

Abstract: The southeastern Guiana Shield, northern Amazonian Craton, is part of a Paleoproterozoic orogenic belt that was built up during the Transamazonian orogenic cycle (2.26-1.95 Ga). This cycle includes large segments of Rhyacian juvenile crust and some reworked Archean terranes. The geology in this region consists mainly of Paleoproterozoic granulitic-migmatitic-gneissic complexes, deformed and metamorphosed metavolcanic and metasedimentary rocks, and granitoids (granitic and TTG magmatism). Three tectonic domains are distinguished in the Brazilian territory of the southeastern Guiana Shield. They are known as the Amapá Block, Lourenço Domain, and Carecuru Domain. The Amapá Block is a Meso-Neoarchean continental block that was intensely reworked during the Transamazonian orogeny. The other two domains represent Rhyacian landmasses, the evolution of which involved several stages of subduction of oceanic lithosphere in magmatic arc environments. There are also relics of reworked Archean continental crust, the formation of which was followed by a collisional stage of tectonic accretion of the magmatic arcs. Whole-rock Sm-Nd and U-Pb zircon geochronology have confirmed the juvenile character of much of this Transamazonian orogenic belt. However, for the Lourenço and Carecuru domains, Nd isotopic signatures indicate the participation of Meso-Neoarchean crustal material in the sources of the magmatic rocks. Combined zircon U-Pb and Lu-Hf isotopic analyses by LA-ICP-MS were performed on eleven Rhyacian granitoids and orthogneisses from the Lourenço and Carecuru domains. The aim was to verify the extension of the influence of the Archean continental crust in the adjacent Paleoproterozoic domains. The main magmatic episodes were identified in the Lourenço Domain (~2.17-2.18, 2.14 and 2.12-2.09 Ga) and Carecuru Domain (2.14 Ga) by U-Pb zircon geochronology. The Lu-Hf isotope data point to the predominance of crustal reworking processes (?Hf(2.2-2.1 Ga) < 0; 67% of zircon crystals) during the formation of Lourenço and Carecuru domains. Hf model ages were found to be mostly Archean (98.4%), even for zircon grains that have positive ?Hf(2.2-2.1 Ga) values. For the terrane at the border of the Lourenço and Carecuru domains with the Amapá Block, assimilation of Archean crust of different ages and proportions in a magmatic arc environment accounts for the Hf-Nd isotopic signatures and Hf model ages of Rhyacian magmatism. In the northwestern part of the Lourenço Domain, more than 100 km north of the Amapá Block, the Hf-Nd isotopic signatures and Hf model ages indicate the participation of Archean crustal material, either as continental fragments and/or through incorporation of continental sediments in island arc environments, similar to what has been recorded for some Birimian terranes of the West African Craton in Ghana.
DS202007-1166
2020
Newcombe, M.E., Plank, T., Barth, A., Asimov, P.D., Hauri, E.Water in olivine magma ascent chronology: every crystal is a clock.Journal of Volcanology and Geothermal Research, Vol. 398, 106872 17p. PdfUnited States, Hawaiimelting

Abstract: The syneruptive decompression rate of basaltic magma in volcanic conduits is thought to be a critical control on eruptive vigor. Recent efforts have constrained decompression rates using models of diffusive water loss from melt embayments (Lloyd et al. 2014; Ferguson et al. 2016), olivine-hosted melt inclusions (Chen et al. 2013; Le Voyer et al. 2014), and clinopyroxene phenocrysts (Lloyd et al. 2016). However, these techniques are difficult to apply because of the rarity of melt embayments and clinopyroxene phenocrysts suitable for analysis and the complexities associated with modeling water loss from melt inclusions. We are developing a new magma ascent chronometer based on syneruptive diffusive water loss from olivine phenocrysts. We have found water zonation in every olivine phenocryst we have measured, from explosive eruptions of Pavlof, Seguam, Fuego, Cerro Negro and Kilauea volcanoes. Phenocrysts were polished to expose a central plane normal to the crystallographic `b' axis and volatile concentration profiles were measured along `a' and `c' axes by SIMS or nanoSIMS. Profiles are compared to 1D and 3D finite-element models of diffusive water loss from olivine, with or without melt inclusions, whose boundaries are in equilibrium with a melt undergoing closed-system degassing. In every case, we observe faster water diffusion along the `a' axis, consistent with the diffusion anisotropy observed by Kohlstedt and Mackwell (1998) for the so-called `proton-polaron' mechanism of H-transport. Water concentration gradients along `a' match the 1D diffusion model with a diffusivity of 10-10 m2/s (see Plank et al., this meeting), olivine-melt partition coefficient of 0.0007­-0.002 (based on melt inclusion-olivine pairs), and decompression rates equal to the best-fit values from melt embayment studies (Lloyd et al. 2014; Ferguson et al. 2016). Agreement between the melt embayment and water-in-olivine ascent chronometers at Fuego, Seguam, and Kilauea Iki demonstrates the potential of this new technique, which can be applied to any olivine-bearing mafic-intermediate eruption using common analytical tools (SIMS and FTIR). In theory, each crystal is a clock, with the potential to record variable ascent in the conduit, over the course of an eruption, and between eruptions.
DS202009-1646
2020
Ni, P., Chabot, N.L., Ryan, C.J., Shahar, A.Heavy iron isotope composition of iron meteorites explained by core crystallization.Nature Geoscience, DOI: 10.1038/ s41561-020-0617-yGlobalmeteorite

Abstract: Similar to Earth, many large planetesimals in the Solar System experienced planetary-scale processes such as accretion, melting and differentiation. As their cores cooled and solidified, substantial chemical fractionation occurred due to solid metal-liquid metal fractionation. Iron meteorites—core remnants of these ancient planetesimals—record a history of this process. Recent iron isotope analyses of iron meteorites found their 57Fe/54Fe ratios to be heavier than chondritic by approximately 0.1 to 0.2 per mil for most meteorites, indicating that a common parent body process was responsible. However, the mechanism for this fractionation remains poorly understood. Here we experimentally show that the iron isotopic composition of iron meteorites can be explained solely by core crystallization. In our experiments of core crystallization at 1,300?°C, we find that solid metal becomes enriched in the heavier iron isotope by 0.13 per mil relative to liquid metal. Fractional crystallization modelling of the IIIAB iron meteorite parent body shows that observed iridium, gold and iron compositions can be simultaneously reproduced during core crystallization. The model implies the formation of complementary sulfur-rich components of the iron meteorite parental cores that remain unsampled by meteorite records and may be the missing reservoir of isotopically light iron. The lack of sulfide meteorites and previous trace element modelling predicting substantial unsampled volumes of iron meteorite parent cores support our findings.
DS202007-1167
2020
Niegisch, M., Kamradt, A., Borg, G.Geochemical and mineralogical characterization of the REE mineralisation in the upper zone of the Storkwitz carbonatite complex from drill core SES-1/2012.Geopril, 15, 92p. PdfEurope, Germanydeposit - Storkwitz

Abstract: The Storkwitz-Carbonatite is a Late Cretaceous intru-sive complex, which is well-explored by a relatively large number of exploration bore holes both from the 1970ies, 1980ies and from one more recent bore hole, SES-1/2012. The carbonatite complex hosts a (cur-rently) marginally economic mineralisation of rare earth elements (REE) and niobium, which is technical-ly still difficult to recover. The upper part of the car-bonatitic body is located some 100-120 m below the Pre-Cenozoic land surface, which in turn is overlain by approximately 100 m of glacial, fluvio-glacial, and fluviatile sediments. The aim of this study was to characterize the minerali-sation in the upper part of the intrusion geochemically and mineralogically and to try to identify indications of a supergene overprint on the late magmatic to hydro-thermal mineralisation. Fresh drill core samples from the exploration bore hole SES-1/2012 have revealed that the mineralisation is associated with a carbonatit-ic igneous breccia body and also with several alvikite veins. The breccia body is very heterogeneous, dis-plays a variety of matrix colours and also a range of matrix-to-clast ratios. Non-destructive analytical methods like p-XRF anal-yses, magnetic susceptibility measurements, and SWIR-reflectance spectroscopy were carried out di-rectly on the drill core. The samples were also investi-gated by optical microscopy, scanning electron mi-croscopy (SEM) and their geochemical composition was analysed by whole rock analyses at a certified laboratory. The geochemical results confirm the presence of a REE-enriched zone, which is closely associated with the carbonatitic intrusion, whereas the porphyritic clasts of the breccia and the porphyritic wall rocks do not contain any REE mineralisation. The mineral composition of the examined sections is very hetero-geneous and comprises magmatic phenocrysts as well as a large variety of secondary mineral phases, which were formed by either hypogene, ascending late magmatic carbothermal or subsequent hydro-thermal processes or alternatively by deeply descend-ing meteoric supergene processes. The secondary processes were strongly oxidising and formed abun-dant hydrated mineral phases. The REE ore minerals are predominantly secondary monazites and REE-fluorocarbonates, which both occur in igneous breccias as well as in alvikite veins. Other minerals such as apatite or pyrochlore are slightly enriched in REE. However, there is no significant correlation be-tween the proportion of REE-bearing minerals ob-served microscopically and the geochemical REE concentration. Several mineral phases display intensive alteration textures and parageneses and especially the crypto-crystalline matrix of the breccias indicate a supergene influence. The supergene overprint has thus caused the alteration and formation of supergene Fe-oxyhydroxides and of an alumo-siliceous matrix and the local redistribution of the REE within the REE-mineral phases. However, no signs were detected that indicate a dissolution, transport, and especially frac-tionation of the dissolved REE in the (deep) super-gene environment.
DS202006-0942
2020
Nikitina, L.P., Goncharov, A.G., Bogomolov, E.S., Beliatsky, B.V., Krimsky, R.Sh., Prichodko, V.S., Babushkina, M.S., Karaman, A.A.HFSE and REE geochemistry and Nd-Sr-Os systematics of peridotites in the subcontinental lithospheric mantle of the Siberian craton and central Asian fold belt junction area: data on mantle xenoliths.Petrology, Vol. 28, 2, pp. 207-219.RussiaREE

Abstract: Mantle xenoliths were found in alkaline basalts of Tokinsky Stanovik (TSt) in the Dzhugdzhur-Stanovoy superterrane (DS) and Vitim plateau (VP) in the Barguzin-Vitim superterrane (BV) (Stanovoy suture area) at junction of the Central Asian Orogenic Belt (CAOB) and the Siberian craton (SC). Xenoliths from TSt basalts are represented by spinel lherzolites, harzburgites, wehrlites; while VP basalts frequently contain spinel-garnet and garnet peridotites lherzolites, and pyroxenites. Xenoliths in kimberlites of the Siberian craton are mainly represented by garnet-bearing lherzolites with abundant eclogite xenoliths (age of 2.7-3.1 Ga), which were not found in mantle of superterranes. The Re-Os determinations point to the Early Archean age of peridotites and eclogites from mantle beneath the Siberian craton. The major and trace (rare-earth and high-filed strength) elements and Nd-Sr-Os composition were analyzed in the peridotites (predominant rocks) of lithospheric mantle at junction of the Central Asian Orogenic Belt and Siberian Craton. The degree of rock depletion in CaO and Al2O3 and enrichment in MgO relative to the primitive mantle in the peridotites of the Dzhugdzhur-Stanovoy superterrane is close to that of the Siberian craton. The peridotites of the Barguzin-Vitim superterrane are characterized by much lower degree of depletion and have mainly a primitive composition. Mantle melting degree reaches up to 45-50% in the Siberian Craton and Dzhugdzhur-Stanovoy superterrane, and is less than 25% in the Barguzin-Vitim terrane. The mantle peridotites of the craton as compared to those of adjacent superterranes are enriched in Ba, Rb, Th, Nb, and Ta and depleted in Y and REE from Sm to Lu. However, all studied peridotites are characterized by mainly superchondritic values of Nb/Ta (>17.4), Zr/Hf (>36.1), Nb/Y (>0.158), and Zr/Y (>2.474). The Nb/Y ratio is predominantly >1.0 in SC peridotites and < 1.0 in the superterrane peridotites. The Nd and Sr isotopic compositions in the latter correspond to those of oceanic basalts. The 187Os/188Os ratio is low (0.108-0.115) in the peridotites of the Siberian Craton and > 0.115 but usually lower than 0.1296 (primitive upper mantle value) in the peridotites of the Dzhugdzhur-Stanovoy and Barguzin-Vitim superterranes. Thus, the geochemical and isotopic composition of peridotites indicates different compositions and types of mantle beneath the Siberian craton and adjacent superterranes of the Central Asian Orogenic Belt in the Early Archean, prior to the formation of 2.7-3.1 Ga eclogites in the cratonic mantle.
DS202008-1426
2020
Nikolenko, A.M., Doroshkevich, A.G., Ponomarchuk, A.V., Redina, A.A., Prokopyev, I.R., Vladykin, N.V., Nikolaeva, I.V.Ar-Ar geochronology and petrogenesis of the Mushgai-Khudag alkaline-carbonatite complex 9 southern Mongolia).Lithos, Vol. 372-372, 105675 15p. PdfAsia, Mongoliacarbonatite

Abstract: The Mushgai-Khudag alkaline?carbonatite complex, located in southern Mongolia within the Central Asian Orogenic Belt (CAOB), comprises a broad range of volcanic and subvolcanic alkaline silicate rocks (melanephelinite-trachyte and shonkinite-alkaline syenite, respectively). Magnetite-apatite rocks, carbonatites, and fluorite mineralization are also manifested in this area. The complex formed between 145 and 133 Ma and is contemporaneous with late Mesozoic alkaline-carbonatite magmatism within the CAOB. Major and trace element characteristics of silicate rocks in the Mushgai-Khudag complex imply that these rocks were formed by the fractional crystallization of alkaline ultramafic parental magma. Magnetite-apatite rocks may be a product of silicate-Ca-Fe-P liquid immiscibility that took place during the alkaline syenite crystallization stage. The Mushgai-Khudag rocks have variable and moderately radiogenic Sr (87Sr/86Sr(i) = 0.70532-0.70614), ?Nd(t) = ?1.23 to 1.25) isotopic compositions. LILE/HFSE values and SrNd isotope compositions indicate that the parental melts of Mushgai-Khudag were derived from a lithospheric mantle source that was affected by a metasomatic agent in the form a mixture of subducted oceanic crust and its sedimentary components. The ?18OSMOW and ?18CPDB values for calcites in carbonatites range from 16.8‰ to 19.2‰ and from ?3.9‰ to 2.0‰, respectively. CO covariations in calcites of the Mushgai-Khudag carbonatites can be explained by the slight host limestone assimilation.
DS202008-1427
2020
Nimis, P., Preston, R., Perritt, S., Chinn, I.Is diamond depth distribution systematic?Goldschmidt 2020, 1p. AbstractAfrica, South Africageobarometry

Abstract: The thermobarometric analysis of inclusions in lithospheric diamonds indicates that they originated from a wide range of depths, with a global mode at ca. 170±15 km [1]. Studies based on diamond depth distribution at global scale, however, cannot clarify if this mode reflects a real concentration of diamonds, preferential sampling of materials from this level by rising kimberlites, or even a statistical distribution within the hard limits imposed by diamond stability, lithosphere thickness, and mantle adiabat under typical cratonic thermal regimes. We addressed this problem by comparing depth distributions for peridotitic diamonds from the three localities that have been the most prolific for diamond geobarometry (Cullinan, Kimberley and Voorspoed, South Africa) with those of mantle xenocrysts from the same kimberlite sources. P-T estimates indicate that the diamonds were formed at T higher, equal or lower than the ambient geotherm. They may record old mantle thermal regimes or local thermal perturbations related to infiltration of parent fluids or melts. Nonetheless, the diamonds show similar depth distributions for different localities, with a distinct mode at ?175 ?? 10 km. The similarity of these distributions with that calculated for peridotitic diamonds worldwide, as well as the lack of systematic correlation with kimberlite sampling efficiency as recorded by mantle xenocrysts, suggests that this mode has genetic significance. Based on observed depth distributions at both local and global scale and on thermodynamic modeling of COH fluids, diamond-forming processes are predicted to become less efficient with decreasing depth from at least ?160 km. In addition, diamond endowment near the base of the lithosphere may be negatively affected by infiltration of carbon-undersaturated melts. Considering the poor correlation between diamond and xenocryst depth distributions in single kimberlites or kimberlite clusters, even limited xenocryst records from diamond favorable depths (especially the 160-190 km interval) may correspond to significant diamond potential.
DS202009-1647
2020
Nimis, P., Preston, R., Perritt, S.H., Chinn, I.L.Diamond's depth distribution systematics. ( geotherm)Lithos, 10.1016/j.lithos. 2020.105729 15p. PdfAfrica, South Africadeposit - Cullinan, Kimberley, Voorspoed

Abstract: The thermobarometric analysis of inclusions in lithospheric diamonds has shown that these diamonds may originate from a wide range of depths, with a global mode at ~175 ± 15 km. Studies based on diamond depth distribution at global scale, however, cannot clarify if this mode reflects a real concentration of diamonds, preferential sampling of materials from this level by ascending kimberlites, or simply a statistical distribution within the hard limits imposed by diamond stability, lithosphere thickness and mantle adiabat under typical cratonic thermal regimes. We addressed this problem by comparing depth distributions for peridotitic diamonds from the three localities that have been the most prolific for diamond geobarometry (Cullinan, Kimberley and Voorspoed, South Africa) with those of mantle xenocrysts from the same kimberlite sources. The revised P-T estimates indicate that the diamonds were formed at T higher, equal or lower than the ambient geotherm recorded by the xenocrysts. These conditions may represent old mantle thermal regimes or local thermal perturbations related to infiltration of parental fluids or melts. Nonetheless, the studied diamonds show similar depth distributions for the different localities, with a distinct mode at ?180 ± 10 km. The similarity of these distributions with that calculated for peridotitic diamonds worldwide, as well as the lack of systematic correlation with kimberlite sampling efficiency as recorded by mantle xenocrysts, suggests that this mode has genetic significance. Based on observed depth distributions and thermodynamic modeling of COH fluids, diamond-forming processes are predicted to become less efficient with decreasing depth from at least ?165 km. In addition, diamond endowment near the base of the lithosphere may be negatively affected by infiltration of carbon-undersaturated melts or fluids after diamond formation. Considering the poor correlation between diamond and xenocryst depth distributions in single kimberlites or kimberlite clusters, even limited xenocryst records from diamond favorable depths (especially from the 160-190 km interval) may correspond to significant diamond potential.
DS202010-1864
2020
Nishiyama, T.Microdiamond in a low grade metapelite from a Cretaceous subduction complex, western Kyushu, Japan.Scientific Reports, doi:10.1038/ s41598-020-68599-7Asia, Japanmicrodiamonds

Abstract: Microdiamonds in metamorphic rocks are a signature of ultrahigh-pressure (UHP) metamorphism that occurs mostly at continental collision zones. Most UHP minerals, except coesite and microdiamond, have been partially or completely retrogressed during exhumation; therefore, the discovery of coesite and microdiamond is crucial to identify UHP metamorphism and to understand the tectonic history of metamorphic rocks. Microdiamonds typically occur as inclusions in minerals such as garnet. Here we report the discovery of microdiamond aggregates in the matrix of a metapelite from the Nishisonogi unit, Nagasaki Metamorphic Complex, western Kyushu, Japan. The Nishisonogi unit represents a Cretaceous subduction complex which has been considered as an epidote-blueschist subfacies metamorphic unit, and the metapelite is a member of a serpentinite mélange in the Nishisonogi unit. The temperature condition for the Nishisonogi unit is 450 °C, based on the Raman micro-spectroscopy of graphite. The coexistence of microdiamond and Mg-carbonates suggests the precipitation of microdiamond from C-O-H fluid under pressures higher than 2.8 GPa. This is the first report of metamorphic microdiamond from Japan, which reveals the hidden UHP history of the Nishisonogi unit. The tectonic evolution of Kyushu in the Japanese Archipelago should be reconsidered based on this finding.
DS202008-1428
2020
Nishiyama, T., Ohfuji, H., Fukuba, K., Terauchi, M., Nishi, U., Harada, K., Unoki, K., Moribe, Y., Yoshiasa, A., Ishimaru, S., Mori, Y., Shigeno, M., Arai, S.Microdiamond in a low grade metapelite from a Cretaceous subduction complex, western Kyushu, Japan. ( UHP) Nishisonogi unitNature Scientific Reports, Vol. 10, 11645 11p. PdfAsia, Japanmicrodiamond

Abstract: Microdiamonds in metamorphic rocks are a signature of ultrahigh-pressure (UHP) metamorphism that occurs mostly at continental collision zones. Most UHP minerals, except coesite and microdiamond, have been partially or completely retrogressed during exhumation; therefore, the discovery of coesite and microdiamond is crucial to identify UHP metamorphism and to understand the tectonic history of metamorphic rocks. Microdiamonds typically occur as inclusions in minerals such as garnet. Here we report the discovery of microdiamond aggregates in the matrix of a metapelite from the Nishisonogi unit, Nagasaki Metamorphic Complex, western Kyushu, Japan. The Nishisonogi unit represents a Cretaceous subduction complex which has been considered as an epidote-blueschist subfacies metamorphic unit, and the metapelite is a member of a serpentinite mélange in the Nishisonogi unit. The temperature condition for the Nishisonogi unit is 450 °C, based on the Raman micro-spectroscopy of graphite. The coexistence of microdiamond and Mg-carbonates suggests the precipitation of microdiamond from C-O-H fluid under pressures higher than 2.8 GPa. This is the first report of metamorphic microdiamond from Japan, which reveals the hidden UHP history of the Nishisonogi unit. The tectonic evolution of Kyushu in the Japanese Archipelago should be reconsidered based on this finding.
DS202003-0353
2018
NMDCPre-feasibility report of Majhgawan diamond mine, Majhgawan, Panna, NMDC Ltd.NMDC Report , 92p. PdfIndiadeposit - Majhgawan
DS202005-0754
2020
Nosova, A.A., Kargin, A.V., Sazonova, L.V., Dubinina, E.O., Chugaev, A.V., Lebedeva, N.M., Yudin, D.S., Larionova, Y.O., Abersteiner, A., Gareev, B.I., Batalin, G.A.Sr-Nd-Pb isotopic systematic and geochronology of ultramafic alkaline magmatism of the southwestern margin of the Siberian craton: metasomatism of the sub-continental lithospheric mantle related to subduction and plume events.Lithos, Vol. 364-365, 21p. PdfRussia, Siberiadeposit - Ilbokich, Chadobets

Abstract: To provide new insights into the origin and evolution of ultramafic lamprophyres (UMLs) and their mantle source, we examined two UML (aillikite and damtjernite) occurrences of different ages in the western portion of the Siberian Craton (Ilbokich and Chadobets). New age, mineral and rock geochemistry, along with Sr-Nd-Pb-C-O isotope data was obtained. Our new 206Pb/238U perovskite age (399 ± 4 Ma) confirms the previously published Early Devonian age of the Ilbokich aillikite. RbSr isochron and 40Ar/39Ar dating yielded a Middle Triassic age (243 ± 3 Ma and 241 ± 1 Ma, respectively) for the Chadobets aillikites, indicating post-Trap emplacement of these rocks. Both UMLs are characterized by incompatible elements, including light rare earth element (LREE) enrichments (La is up to ×200 chondrite concentration), and strong fractionation of REEs ((La/Yb)n: 33-84). Despite the close geochemical affinity of both UMLs, the Nd isotopic compositions of aillikites, as well as the Pb isotopic composition of Chadobets and Ilbokich UMLs, do not overlap and are distinctly different from each other. The initial Sr and Nd isotopic compositions of the Ilbokich UMLs fall in within a narrow 87Sr/86Sr0 range (0.7032-0.7042) and ?Nd(T) (4.03-3.97). Chadobets UMLs have a similar Sr isotopic signature (87Sr/86Sr0: 0.7031-0.7043) and a more depleted Nd isotopic signature (?Nd(T) 4.09-5.08). The initial Pb isotope compositions of the Chadobets UMLs are moderately radiogenic, ranging between 206Pb/204Pb = 18.4-19.0, 208Pb/204Pb = 38.3-38.8, and are characterized by a narrow 207Pb/204Pb ratio between 15.5 and 15.6. The Ilbokich Pb isotope compositions are less variable and range between 206Pb/204Pb = 18.0-18.4, 208Pb/204Pb = 37.8-38.4 and 207Pb/204Pb ratios between 15.5 and 15.6. The oxygen isotopic composition of carbonate from both UMLs is characterized by highly variable ?18O values from +12.1 and up to +20.5‰ (SMOW). The isotopic composition of ?13C values range from ?1.3‰ to ?7.1. Based on the minor impact of crustal contamination in both aillikites, it is inferred that their radiogenic isotope composition reflects a mantle source signature. The mantle source of the Chadobets aillikites is likely to include carbonatitic magma as a metasomatic agent. In contrast, phlogopite-rich metasomes within the lithospheric mantle could have contributed more significantly to the Ilbokich aillikites. These metasomes could be formed during the Caledonian orogeny, which did not only affect the southwestern boundary of the Siberian Craton, but also expanded to the craton interior. This study provides additional support for the evolution of the south-western portion of the Siberian SCLM, ranging from mantle containing phlogopite enrichment domains during the Early Devonian to hydrous-phase reduced mantle in the Triassic due to the thermal impact of the Siberian Traps.
DS202006-0943
2020
Novosa, A.A., Kargin, A.V., Sazonova, L.V., Dubinina, E.O., Chugaev, A.V., Lebedeva, N.M., Yudin, D.S., Larionova, Y.O., Abersteiner, A., Gareev, B.I., Batalin, G.A.Sr-N-Pb isotopic systematic and geochronology of ultramafic alkaline magmatism of the southwestern margin of the Siberian craton: metasomatism of the sub-continental lithospheric mantle related to subduction and plume events.Lithos, Vol. 364-365, 21p. PdfRussiaailikite, damjernite

Abstract: To provide new insights into the origin and evolution of ultramafic lamprophyres (UMLs) and their mantle source, we examined two UML (aillikite and damtjernite) occurrences of different ages in the western portion of the Siberian Craton (Ilbokich and Chadobets). New age, mineral and rock geochemistry, along with Sr-Nd-Pb-C-O isotope data was obtained. Our new 206Pb/238U perovskite age (399 ± 4 Ma) confirms the previously published Early Devonian age of the Ilbokich aillikite. RbSr isochron and 40Ar/39Ar dating yielded a Middle Triassic age (243 ± 3 Ma and 241 ± 1 Ma, respectively) for the Chadobets aillikites, indicating post-Trap emplacement of these rocks. Both UMLs are characterized by incompatible elements, including light rare earth element (LREE) enrichments (La is up to ×200 chondrite concentration), and strong fractionation of REEs ((La/Yb)n: 33-84). Despite the close geochemical affinity of both UMLs, the Nd isotopic compositions of aillikites, as well as the Pb isotopic composition of Chadobets and Ilbokich UMLs, do not overlap and are distinctly different from each other. The initial Sr and Nd isotopic compositions of the Ilbokich UMLs fall in within a narrow 87Sr/86Sr0 range (0.7032-0.7042) and ?Nd(T) (4.03-3.97). Chadobets UMLs have a similar Sr isotopic signature (87Sr/86Sr0: 0.7031-0.7043) and a more depleted Nd isotopic signature (?Nd(T) 4.09-5.08). The initial Pb isotope compositions of the Chadobets UMLs are moderately radiogenic, ranging between 206Pb/204Pb = 18.4-19.0, 208Pb/204Pb = 38.3-38.8, and are characterized by a narrow 207Pb/204Pb ratio between 15.5 and 15.6. The Ilbokich Pb isotope compositions are less variable and range between 206Pb/204Pb = 18.0-18.4, 208Pb/204Pb = 37.8-38.4 and 207Pb/204Pb ratios between 15.5 and 15.6. The oxygen isotopic composition of carbonate from both UMLs is characterized by highly variable ?18O values from +12.1 and up to +20.5‰ (SMOW). The isotopic composition of ?13C values range from ?1.3‰ to ?7.1. Based on the minor impact of crustal contamination in both aillikites, it is inferred that their radiogenic isotope composition reflects a mantle source signature. The mantle source of the Chadobets aillikites is likely to include carbonatitic magma as a metasomatic agent. In contrast, phlogopite-rich metasomes within the lithospheric mantle could have contributed more significantly to the Ilbokich aillikites. These metasomes could be formed during the Caledonian orogeny, which did not only affect the southwestern boundary of the Siberian Craton, but also expanded to the craton interior. This study provides additional support for the evolution of the south-western portion of the Siberian SCLM, ranging from mantle containing phlogopite enrichment domains during the Early Devonian to hydrous-phase reduced mantle in the Triassic due to the thermal impact of the Siberian Traps.
DS202006-0944
2020
O'Bannon, E., Xia, G., Shi, F., Wirth, R., King, R.A., Dobrzhinetskaya, L.The transformation of diamond to graphite: experiments reveal the presence of an intermediate linear carbon phase. Diamonds & Related Materials, in press available, 31p. PdfGlobalcarbon

Abstract: Natural diamonds that have been partially replaced by graphite have been observed to occur in natural rocks. While the graphite-to-diamond phase transition has been extensively studied the opposite of this (diamond to graphite) remains poorly understood. We performed high-pressure and temperature hydrous and anhydrous experiments up to 1.0?GPa and 1300?°C using Amplex premium virgin synthetic diamonds (20-40??m size) as the starting material mixed with Mg (OH)2 as a source of H2O for the hydrous experiments. The experiments revealed that the diamond-to-graphite transformation at P?=?1GPa and T?=?1300?°C was triggered by the presence of H2O and was accomplished through a three-stage process. Stage 1: diamond reacts with a supercritical H2O producing an intermediate 200-500?nm size “globular carbon” phase. This phase is a linear carbon chain; i.e. a polyyne or carbyne. Stage 2: the linear carbon chains are unstable and highly reactive, and they decompose by zigzagging and cross-linking to form sp2-bonded structures. Stage 3: normal, disordered, and onion-like graphite is produced by the decomposition of the sp-hybridized carbon chains which are re-organized into sp2 bonds. Our experiments show that there is no direct transformation from sp3 C-bonds into sp2 C-bonds. Our hydrous high-pressure and high-temperature experiments show that the diamond-to-graphite transformation requires an intermediate metastable phase of a linear hydrocarbon. This process provides a simple mechanism for the substitution of other elements into the graphite structure (e.g. H, S, O).
DS202009-1648
2019
Ogden, J.History, heritage and hype behind Golgonda diamondsGems & Jewellery, Vol. 29, 3, autumn pp. 38-40.Indiadeposit - Golconda
DS202009-1649
2020
Okuda, Y., Ohta, K., Haseawa, A., Yagi, T., Hirose, K., Kawaguchi, S.I., Ohishi, Y.Thermal conductivity of Fe bearing post- perovskite in the Earth's lowermost mantle.Earth and Planetary Science Letters, Vol. 547, 9p. PdfMantleperovskite

Abstract: The thermal conductivity of post-perovskite (ppv), the highest-pressure polymorph of MgSiO3 in the Earth's mantle, is one of the most important transport properties for providing better constraints on the temperature profile and dynamics at the core-mantle boundary (CMB). Incorporation of Fe into ppv can affect its conductivity, which has never been experimentally investigated. Here we determined the lattice thermal conductivities of ppv containing 3 mol% and 10 mol% of Fe at high P-T conditions - of pressures up to 149 GPa and 177 GPa, respectively, and temperatures up to 1560 K - by means of the recently developed pulsed light heating thermoreflectance technique combining continuous wave heating lasers. We found that the incorporation of Fe into ppv moderately reduces its lattice thermal conductivity as it increases the Fe content. The bulk conductivity of ppv dominant pyrolite is estimated as 1.5 times higher than that of pyrolite consisting of bridgmanite and ferropericlase in the lower mantle, which agrees with the traditional view that ppv acts as a better heat conductor than bridgmanite in the Earth's lowermost mantle.
DS202002-0213
2020
Okyay, U., Telling, J., Glennie, C.L., Dietrich, W.E.Airborne lidar change detection: an overview of Earth science applications. ( not specific to diamonds)Earth Science Reviews, Vol. 198, 25p. PdfGlobalLidar

Abstract: In the last two decades, airborne laser scanning (ALS) has found widespread application and driven fundamental advances in the Earth sciences. With increasing availability and accessibility, multi-temporal ALS data have been used to advance key research topics related to dynamic Earth surface processes. This review presents a comprehensive compilation of existing applications of ALS change detection to the Earth sciences. We cover a wide scope of material pertinent to the broad field of Earth sciences to encourage the cross-pollination between sub-disciplines and discuss the outlook of ALS change detection for advancing scientific discovery. While significant progress has been made in applying repeat ALS data to change detection, numerous approaches make fundamental assumptions that limit the full potential of repeat ALS data. The use of such data for 3D change detection is, therefore, in need of novel, scalable, and computationally efficient processing algorithms that transcend the ever-increasing data density and spatial coverage. Quantification of uncertainty in change detection results also requires further attention, as it is vitally important to understand what 3D differences detected between epochs represent actual change as opposed to limitations in data or methodology. Although ALS has become increasingly integral to change detection across the Earth sciences, the existence of pre- and post-event ALS data is still uncommon for many isolated hazard events, such as earthquakes, volcanic eruptions, wildfires, and landslides. Consequently, data availability is still a major limitation for many ALS change detection applications.
DS202003-0354
2020
O'Neill, C., March, S., Bottke, W., Fu, R.The role of impacts in Archean tectonics.Geology, Vol. 48, pp. 174-178.Australia, Africa, South Africacraton

Abstract: Field evidence from the Pilbara craton (Australia) and Kaapvaal craton (South Africa) indicate that modern tectonic processes may have been operating at ca. 3.2 Ga, a time also associated with a high density of preserved Archaean impact indicators. Recent work has suggested a causative association between large impacts and tectonic processes for the Hadean. However, impact flux estimates and spherule bed characteristics suggest impactor diameters of <100 km at ca. 3.5 Ga, and it is unclear whether such impacts could perturb the global tectonic system. In this work, we develop numerical simulations of global tectonism with impacting effects, and simulate the evolution of these models throughout the Archaean for given impact fluxes. We demonstrate that moderate-size (?70 km diameter) impactors are capable of initiating short-lived subduction, and that the system response is sensitive to impactor size, proximity to other impacts, and also lithospheric thickness gradients. Large lithospheric thickness gradients may have first appeared at ca. 3.5-3.2 Ga as cratonic roots, and we postulate an association between Earth’s thermal maturation, cratonic root stability, and the onset of widespread sporadic tectonism driven by the impact flux at this time.
DS202001-0032
2020
Otamonga, J-P., Pote, J.W.Abandoned mines and artisanal and small scale mining in Democratic Republic of Congo ( DRC): survey and agenda for future research.Journal of Geochemical Exploration, Vol. 208, 106394Africa, Democratic Republic of Congoalluvials

Abstract: The Democratic Republic of the Congo (DRC) has a long history of mining activities. However, environmental and socio-economic problems associated with abandoned mines as well as activities including Artisanal and Small-Scale Mining (ASM) remain very concerning issues throughout the country. In this paper, we review abandoned mines, Artisanal and Small-Scale Mining (ASM), environmental and human impact assessment, conflict-minerals, and perspectives for future researches on mining activities in DRC, by selecting 26 significant and relevant peer-reviewed papers. With the recent mining boom in DRC, the issue of social and environmental impacts of abandoned mines and ASM has become a matter of concern for Congolese people. This actual development of several mining projects has driven the development of regulation, monitoring and impact assessment, and scientific publications of these activities. However, the findings from multiple studies regarding the impacts of abandoned mines and artisanal and small-scale mining on the environment and human health across the country has not yet been sufficiently brought together in a reliable way. Focusing on health, social and environmental issues, this mini-review aims to increase awareness of negative impacts of mining operations and promote further collaborative between citizens, mining companies, government institutions and other stakeholders with the hope to reduce negative impacts associated with minerals and metals mining and to extend the benefits to the surrounding Congolese communities. The overarching objective of this paper is to characterize the existing studies in the field of the impact assessment of abandoned mines and ASM on public health and environment with a view to stimulate research, guide development of policies and implementation of appropriate interventions. This report draws from material published and available in the public domain over the past years. It also explores the response of the state and the mining companies to these issues, exploring responses such as regulatory changes and implementations of existing legislation. According to the results, additional studies that examine the relationship between minerals mining, bioremediation processes, training and dialogue aspects and the associated adverse environmental and health outcomes are needed to more adequately characterize the impact of mining activities on health and environment, in order to increase formalization of artisanal and small-scale mining sector while strengthening their social and environmental responsibility, and promoting sustainable mining practice standards that improve people lives and respect the environment in DRC.
DS202012-2237
2020
Palin, R.M., Santosh, M.Plate tectonics: what, where, why, and when?Gondwana Research, in proof available, 105p. Pdf 10.1016/j.gr.2020.11.001Globalplate tectonics
DS202007-1168
2020
Palin, R.M., Santosh, M., Cao, W., Li, S-S., Hernandez-Uribe, D.Secular change and the onset of plate tectonics on Earth.Earth Science Reviews, in press available 41p. PdfMantleplate tectonics

Abstract: The Earth as a planetary system has experienced significant change since its formation c. 4.54 Gyr ago. Some of these changes have been gradual, such as secular cooling of the mantle, and some have been abrupt, such as the rapid increase in free oxygen in the atmosphere at the Archean-Proterozoic transition. Many of these changes have directly affected tectonic processes on Earth and are manifest by temporal trends within the sedimentary, igneous, and metamorphic rock record. Indeed, the timing of global onset of mobile-lid (subduction-driven) plate tectonics on our planet remains one of the fundamental points of debate within the geosciences today, and constraining the age and cause of this transition has profound implications for understanding our own planet's long-term evolution, and that for other rocky bodies in our solar system. Interpretations based on various sources of evidence have led different authors to propose a very wide range of ages for the onset of subduction-driven tectonics, which span almost all of Earth history from the Hadean to the Neoproterozoic, with this uncertainty stemming from the varying reliability of different proxies. Here, we review evidence for paleo-subduction preserved within the geological record, with a focus on metamorphic rocks and the geodynamic information that can be derived from them. First, we describe the different types of tectonic/geodynamic regimes that may occur on Earth or any other silicate body, and then review different models for the thermal evolution of the Earth and the geodynamic conditions necessary for plate tectonics to stabilize on a rocky planet. The community's current understanding of the petrology and structure of Archean and Proterozoic oceanic and continental crust is then discussed in comparison with modern-day equivalents, including how and why they differ. We then summarize evidence for the operation of subduction through time, including petrological (metamorphic), tectonic, and geochemical/isotopic data, and the results of petrological and geodynamical modeling. The styles of metamorphism in the Archean are then examined and we discuss how the secular distribution of metamorphic rock types can inform the type of geodynamic regime that operated at any point in time. In conclusion, we argue that most independent observations from the geological record and results of lithospheric-scale geodynamic modeling support a global-scale initiation of plate tectonics no later than c. 3 Ga, just preceding the Archean-Proterozoic transition. Evidence for subduction in Early Archean terranes is likely accounted for by localized occurrences of plume-induced subduction initiation, although these did not develop into a stable, globally connected network of plate boundaries until later in Earth history. Finally, we provide a discussion of major unresolved questions related to this review's theme and provide suggested directions for future research.
DS202003-0355
2019
Palke, A.C., Saeseaw, S., Renfro, N.D., Sun, Z., McClure, S.F.Geographic origin of ruby.Gems & Gemology, Vol. 55, 4, pp. 580-579.Global, Asia, Myanmar, Vietnam, Cambodia, Thailand, Africa, Madagascar, Mozambique, Europe, Afghanistanruby

Abstract: Over the last several decades, geographic origin determination for fine rubies has become increasingly important in the gem trade. In the gemological laboratory, rubies are generally broken down into two groups based on their trace element chemistry: marble-hosted (low-iron) rubies and high-iron rubies. High-iron rubies are usually a straightforward identification based on their inclusions and trace element profiles. Marble-hosted rubies can be more challenging, with some deposits showing overlap in some of their inclusion scenes. But many marblehosted rubies, especially Burmese stones from Mogok and Mong Hsu, can be accurately identified based on their internal features and trace element profiles. This contribution will outline the methods and criteria used at GIA for geographic origin determination for ruby.
DS202008-1429
2020
Palmato, M.G., Nestola, F., Novella, D, Pearson, D.G., Stachel, T.In-situ mineralogical characterization of sulphide inclusions in diamonds.Goldschmidt 2020, 1p. AbstractCanada, Ontariodeposit - Victor

Abstract: Among mineral inclusions in diamond, sulphides are the most abundant. Also, they are the keel tool for dating diamond formation given their high concentration of highlysiderophile elements. However, the mineralogical nature of these inclusions is not well understood, mainly due to the exsolution of the original, high temperature monosulphide solid solution (Mss) to Fe-, Ni- and Cu-rich endmembers during cooling, obscuring the original composition. This complex exsolution observed in sulphide inclusions in diamonds can also cause problems with Re-Os age determinations if the whole inclusion is not extracted. To overcome this issue, recently, sulphide inclusions have been homogenized at high temperature and controlled oxygen fugacity [1]. However, X-ray diffraction or Raman spectroscopy analyses, required to accurately identify the inclusion phases, and define their degree of crystallographic plus compositional homogeneity, have not been reported. Here we combine for the first time a thorough nondestructive multi-technique characterization of sulphide inclusions in diamonds from the Victor Mine (Canada) with homogenization experiments and isotopic analyses. In particular, we report X-ray diffraction data of the sulphides before and after homogenization, confirming a change from a polycrystalline assemblage of pyrrothite, pentlandite and chalcopyrite to single-crystal Mss. The data are used to reconstruct the Mss’ original bulk composition, define the true bulk isotopic ratios and document any difference in Re- Os isotope systematics.
DS202007-1169
2020
Pandey, A., Chalapathi Rao, N.V.Supercontinent transition as a trigger for ~1.1 Gyr diamondiferous kimberlites and related magmatism in India. ( Dharwar and Bastar cratons)Lithos, Vol. 370-371, 105620, 11p. PdfIndialamproites

Abstract: Kimberlites are volatile-rich deep mantle-derived rocks that often contain diamonds. Numerous Grenvillian (ca. 1.1 Gyr) diamondiferous kimberlites, ultramafic lamprophyres, and lamproites are exposed in the Eastern Dharwar Craton and the Bastar Craton, India, and are aligned almost parallel to the Eastern Ghats (granulite) Mobile Belt (EGMB). The trigger for these kimberlite and related magmatic events still remains an open question. We review the available geochronological and radiogenic isotopic data for the ~1.1 Gyr kimberlites, lamproites, and ultramafic lamprophyres from the Eastern Dharwar Craton and the Bastar Craton of the Indian shield. We show that kimberlites and associated magmas were emplaced for a longer duration (ca. 130 Myr) in the Indian shield during the Mesoproterozoic and sampled distinct mantle source regions. The kimberlites and ultramafic lamprophyre are characterized by slightly depleted to chondritic Nd isotopic ratios revealing their origin at deeper sub-lithospheric regions, whereas the lamproites essentially show an enriched Nd isotopic signature suggesting their derivation from enriched sub-continental lithospheric mantle. We argue that the absence of linear age progression, prolonged magmatic activity compared to the time span of coeval large igneous provinces (the Umkondo, the Keweenawan, and the Warakurna) and a cooler ambient mantle as revealed from the entrained xenoliths, constitute important limitations for a plume model earlier proposed for the genesis of these kimberlites and related magmas. These observations together with a geographical and temporal (Grenvillian) link to the EGMB points towards edge-driven convection as a trigger for kimberlite magmatism- similar to the model proposed for the Mid-Cretaceous kimberlite corridor in North America. However, this model can't explain the coeval formation of sub-continental lithospheric mantle-derived lamproites. As the timing of kimberlite and related magmatism coincides with that of the Grenvillian orogeny and succeeded a magmatic lull of ~360 Myr in the Dharwar Craton during the Mesoproterozoic, we instead, propose that small scale partial melting of heterogeneous mantle caused by plate reorganization during Columbia to Rodinia supercontinent extroversion served as a trigger for this ca. 1.1 Gyr magmatism in the southeastern Indian shield.
DS202008-1430
2020
Pandey, A., Chalapathi Rao, N.V.Geochemical insights into the distinct mantle sources of coeval shoshonitic lamprophyres and kimberlites from the Wajrakarur kimberlite field, Dharwar craton.Goldschmidt 2020, 1p. AbstractIndiadeposit - Wajakarur

Abstract: The Eastern Dharwar Craton (EDC) of the southern Indian shield host numerous Mesoproterozoic (~1100 Ma) kimberlite fields. Shoshonitic lamprophyre dykes synchronous to these kimberlites are exposed in the diamondiferous Wajrakarur kimberlite field (WKF). These lamprophyre dykes are characterized by the presence of olivine, biotite and zoned clinopyroxene phenocrysts set in a groundmass of feldspar, spinel and apatite. High K2O/Na2O (1.5-3.4) along with elevated Th content (2.2-8.6) in these dykes reveal their shoshonitic affinity. High Th/Yb (1.5-4.1), Nb/Yb (23.8-59.0) and superchondritic Zr/Hf ratios (40-50.4) similar to the oceanic island basalts rules out crustal assimilation and highlights the role of an enriched mantle source in their genesis. Age corrected bulk-rock ?Nd of the shoshonitic lamprophyres vary between -13.73 and -22.90, whereas the initial 87Sr/86Sr ranges between and 0.70533-0.71218 suggesting their derivation from an enriched lithospheric mantle. However, the coeval kimberlites of the WKF have distinct Sr-Nd isotopic composition with bulk-rock ?Nd and initial 87Sr/86Sr varying from 0.44 to 2.75 and 0.70209 to 0.70744, respectively, similar to that of the groundmass perovskite ?Nd (2.08-2.92) and initial 87Sr/86Sr (0.70234- 0.70255). Since, these kimberlites tap an isotopically depleted mantle source, unlike the shoshonitic lamprophyres, the geochemistry of these rocks points to a vertically heterogeneous lithospheric mantle beneath the EDC. We suggest that the Wajrakarur kimberlites generated from a deeper depleted mantle (>150 km) compared to the shallower enriched lithospheric mantle source for the shoshonitic lamprophyres. Neoarchean (2.6-2.8 Ga) Nd depleted mantle model ages for these lamprophyres suggest that the subcontinental lithospheric mantle was enriched during Neoarchean accretion-related evolution of the Dharwar Craton.
DS202011-2057
2020
Pandey, A., Chalapathi Rao, N.V., Chakrabarti, R.Mesoproterozoic 40 Ar/39 Ar age and Sr-Nd isotopic geochemistry of calc- alkaline lamprophyre from the Mudigubba area, eastern Dharwar craton, India.Current Science, Oct. 8p. PdfIndialamprophyre

Abstract: We report a 40Ar/39Ar Mesoproterozoic radiometric age for a calc-alkaline lamprophyre dyke from the Mudigubba area towards the western margin of the Cuddapah Basin, Eastern Dharwar Craton (EDC), Southern India. Amphibole phenocryst separates from this lamprophyre yielded a plateau age of 1169 ± 8 Ma (2? ), which is almost 50 million years older than the majority of radiometric dates available for the Wajrakarur field kimberlites which are proximal to this dyke. Bulk-rock Sr-Nd isotopic analyses of the Mudigubba lamprophyre dykes (?Nd(t) between -13.3 and -12.4) reveal their derivation from an old, enriched, continental lithospheric mantle unlike the kimberlites (bulk-rock and perovskite in situ ?Nd(t) between -0.77 and +7.93), which originated either from a chondritic or depleted mantle source. This study provides further evidence for emplacement of compositionally distinct, mantle-derived Mesoproterozoic alkaline magmas in the EDC and highlights the extremely heterogeneous character of the lithospheric mantle beneath this craton.
DS202005-0755
2017
Pandey, A., Chalapathi Rao, N.V., Pandit, D., Pankaj, P., Pandey, R., Sahoo, S.Subduction - tectonics in the evolution of the eastern Dharwar craton, southern India: insights from the post-collisional calc-alkaline lamprophyres at the western margin of the Cuddapah Basin.Precambrian Research, in press available, 17p. PdfIndiacraton

Abstract: The geodynamic evolution of the eastern Dharwar craton, southern India, is widely debated with a number of contrasting models ranging from uniformitarian plate convergence to the mantle plume and their combination. We report here the petrology and geochemistry of two undeformed and unmetamorphosed lamprophyre dykes from the Mudigubba area located immediately towards the western margin of the Paleo-Mesoproterozoic Cuddapah basin from this craton. The Mudigubba lamprophyres are free from crustal xenoliths, and have a typical porphyritic-panidiomorphic texture predominated by phenocrysts of amphibole. Clinopyroxene occurs as microphenocrysts with feldspar essentially confined to the groundmass. F-rich apatite and sphene are the other accessories. Mineral chemistry reveals that the amphiboles are of calcic variety (dominantly magnesio-hornblende), the clinopyroxene to be a diopside (Wo45.01-50.40 En36.74-44.58 Fs6.79-12.73 Ac0.42-2.24) and the albitic (Or1.12 Ab91.17 An7.70) nature of the feldspar. The lower abundance of TiO2 in both the amphibole and clinopyroxene, suggest a calc-alkaline nature of the magma. High Mg# (76.8-79.3), Ni (140-240 ppm) and Cr (380-830 ppm) contents along with (i) depletion in U, and Th, (ii) variable Ba/La and (iii) low Nb/La as well as Th/La strikes out possibility of crustal contamination and supports the primary nature of the lamprophyre magma. The presence of significant Nb-Ta, Zr-Hf and Ti negative anomalies in the primitive mantle normalized multi-element plots and their striking similarity with the global calc-alkaline lamprophyres imply the involvement of subduction-related mantle source modification. Various geochemical ratios (e.g., Hf/Sm, Ta/La, Th/Yb, Nb/Yb, La/Nb, Ba/Nb) demonstrate the source enrichment was caused by a fluid-related, rather than silicate-melt related, subduction metasomatism. Binary-mixing calculations assuming average upper crust and N-MORB as the two end members reveals ?10-30% influx of subducted component in the generation of the Mudigubba lamprophyres. A re-examination of the limited geochemical data available for the co-spatial Paleoproterozoic (2200-1600 Ma) alkaline plutons suggests this Neoarchaean subduction-event in this domain could in fact be a regional feature - all along the western margin of the Cuddapah basin and represents a hitherto unrecognised suture zone in the eastern Dharwar craton with the Paleoproterozoic (?) emplacement of Mudigubba lamprophyres post-dating this collisional event. Our findings provide significant geochemical support to the models invoking convergence towards the evolution of the Eastern Dharwar craton and impose important constraints on the geodynamics of the southern peninsular India.
DS202008-1431
2020
Pankaj, P., Giri, R.K., Chalapathi Rao, N.V., Charabarti, R., Raghuvanshi, S.Mineralogy and petrology of shoshonitic lamprophyre dykes from the Sivarampeta area, diamondiferous Wajrakarur kimberlite field, eastern Dharwar craton, southern India.Journal of Mineralogical and petrological Sciences, Vol. 115, 2, pp. 202-215. pdfIndiadeposit - Wajrakarur

Abstract: Petrology and geochemistry (including Sr and Nd isotopes) of two lamprophyre dykes, intruding the Archaean granitic gneisses at Sivarampeta in the diamondiferous Wajrakarur kimberlite field (WKF), eastern Dharwar craton, southern India, are presented. The Sivarampeta lamprophyres display porphyritic-panidiomorphic texture comprising macrocrysts/phenocrysts of olivine, clinopyroxene (augite), and mica set in a groundmass dominated by feldspar and comprising minor amounts of ilmenite, chlorite, carbonates, epidote, and sulphides. Amphibole (actinolite-tremolite) is essentially secondary in nature and derived from the alteration of clinopyroxene. Mica is compositionally biotite and occurs as a scattered phase throughout. Mineralogy suggests that these lamprophyres belong to calc-alkaline variety whereas their bulk-rock geochemistry portrays mixed signals of both alkaline as well as calc-alkaline (shoshonitic) variety of lamprophyres and suggest their derivation from the recently identified Domain II (orogenic-anorogenic transitional type mantle source) from eastern Dharwar craton. Trace element ratios imply melt-derivation from an essentially the garnet bearing-enriched lithospheric mantle source region; this is further supported by their 87Sr/86Srinitial (0.708213 and 0.708507) and ‘enriched’ ?Ndinitial (?19.1 and ?24.2) values. The calculated TDM ages (2.7-2.9 Ga) implies that such enrichment occurred prior to or during Neoarchean, contrary to that of the co-spatial and co-eval kimberlites which originated from an isotopically depleted mantle source which was metasomatized during Mesoproterozoic. The close association of calc-alkaline shoshonitic lamprophyres, sampling distinct mantle sources, viz., Domain I (e.g., Udiripikonda) and Domain II (Sivarampeta), and kimberlites in the WKF provide further evidence for highly heterogeneous nature of the sub-continental lithospheric mantle beneath the eastern Dharwar craton.
DS202011-2058
2020
Pappas, S.Rare magnetism found in world's strongest material. GrapheneLive Science, Oct. 14, 2p.Globalgraphene
DS202012-2238
2019
Park, S.J., Ungson, G.R.Rough diamonds in emerging markets: legacy, Competitiveness, and sustained high performance.Cross Cultural & Strategic Management, Vol. 26, 3, pp. 363-386.GlobalBlank

Abstract: The purpose of this paper is to uncover the underlying drivers of sustained high performing companies based on a field study of 127 companies in Brazilian, Russian, Indian and Chinese (BRIC) and Association of Southeast Asian Nations (ASEAN) emerging markets. Understanding these companies provides a complementary way of appraising the growth, development and transformation of emerging markets. The authors synthesize the findings in an overarching framework that covers six strategies for building and sustaining legacy that leads to the succession of intergenerational wealth over time: overcoming institutional voids, inclusive markets, deepening localization, nurturing government support, building core competencies and harnessing human capital. The authors relate these strategies to different levels of development using Prahalad and Hart’s BOP framework.
DS202010-1865
2020
Pashkevich, M.A., Alekseenko, A.V.Reutilization prospects of diamond clay tailings at the Lomonosov mine, northwestern Russia.Minerals, Vol. 10, 517 10.3390/min10060517 17p. PdfRussiadeposit - Lomonosov

Abstract: Approaches to reutilization of diamond clay tailings in northern environments are considered in the example of the Subarctic region of Russia. The monitoring studies are conducted at storage facilities of Severalmaz PJSC where ca. 14 million cubic meters of waste rock are produced annually after kimberlite mining and processing. The tailings of diamond ore dressing waste are situated in complex geological conditions of high-groundwater influx and harsh cold climate with low levels of solar radiation and the average annual temperature below freezing point. Furthermore, the adjoining protected forests with a significant diversity of biogeocenoses and salmon-spawning rivers are affected by the storage area. Reducing the impact of the tailings can be achieved through the reuse of the stored clay magnesia rocks obtained from saponite-containing suspension. The experiments reveal the most promising ways of their application as potential secondary mineral raw materials: cement clinker and ceramics manufacture, integration of alkaline clay into the reclamation of acidic peat bogs, and production of aqueous clay-based drilling fluid. Field and laboratory tests expose the advantages and prospects of each suggested treatment technique.
DS202006-0945
2020
Pasteris, J.D., Beyssac, O.Welcome to raman spectroscopy: successes, challenges, and pitfalls.Elements, Vol. 16, pp. 87--92.MantleSpectroscopy

Abstract: Geoscientists quickly recognized the broad applicability of Raman micro-probe spectroscopy to the Earth and planetary sciences, especially after commercially built microprobe instruments became available in the early 1980s. Raman spectra are sensitive to even minor (chemical or structural) perturbations within chemical bonds in (even amorphous) solids, liquids, and gases and can, thus, help identify, characterize, and differentiate between individual minerals, fluid inclusions, glasses, carbonaceous materials, solid solution phases, strain in minerals, and dissolved species in multi-component solutions. The articles in this issue explore how Raman spectroscopy has deepened and broadened our understanding of geological and extraterrestrial materials and processes.
DS202005-0756
2020
Pati, J.K.Evolution of Bundelkhand craton.Episodes ( IUGS), Vol. 43, 1, pp. 69-87.Indiacraton

Abstract: The Indian subcontinent is a repository of Archean cratonic nuclei with plethora of geoscientific data to better understand the early Earth evolution and the operating processes. The Bundelkhand Craton (BuC) in the north-central India is one of the five Archean cratons which preserves signatures of Paleoarchean magmatism, Archean subduction, Neoarchean metamorphism, spectacular craton-scale landforms as a testimony of Paleoproterozoic episodic silico-thermal fluid activity and plume-generated mafic magmatism, and a Paleoproterozoic meteoritic impact event, currently the seventh oldest in the world. Based on available geological and geophysical data, the BuC has been divided into north BuC (NBuC) and south BuC (SBuC) across the Bundelkhand Tectonic Zone (BTZ). The evolution of BuC has many similarities with other Indian cratons and the available geochronological data suggest that it forms a part of the Ur Supercontinent.
DS202009-1650
2020
Pati, J.K.Evolution of Bundelkhand craton.Episodes, Vol. 43, 1, pp. 69-80.Indiacraton
DS202008-1432
2020
Patocka, V., Sramek, O., Tosi, N.Minimum heat flow from the core and thermal evolution of the Earth.Physics of the Earth and Planetary Interiors, Vol. 305, 106457, 17p. PdfMantlegeothermometry

Abstract: The role of heat flow coming from the core is often overlooked or underestimated in simple models of Earth's thermal evolution. Throughout most of Earth's history, the mantle must have been extracting from the core at least the amount of heat that is required to operate the geodynamo. In view of recent laboratory measurements and theoretical calculations indicating a higher thermal conductivity of iron than previously thought, the above constraint has important implications for the thermal history of the Earth's mantle. In this work we construct a paramaterized mantle convection model that treats both the top and the core-mantle boundary heat fluxes according to the boundary layer theory, or alternatively employs the model of Labrosse (2015) to compute the thermal evolution of the Earth's core. We show that the core is likely to provide all the missing heat that is necessary in order to avoid the so-called “thermal catastrophe” of the mantle. Moreover, by analyzing the mutual feedback between the core and the mantle, we provide the necessary ingredients for obtaining thermal histories that are consistent with the petrological record and have reasonable initial conditions. These include a sufficiently high viscosity contrast between the lower and upper mantle, whose exact value is sensitive to the activation energy that governs the temperature dependence of the viscosity.
DS202005-0757
2020
Patranabis-Deb, S., Saha, S.Geochronology, paleomagnetic signature and tectonic models of cratonic basins of India in the backdrop of supercontinent amalgamation and fragmentation.Episodes ( IUGS), Vol. 43, 1, pp. 145-163.Indiacraton

Abstract: The Proterozoic cratonic basins of peninsular India preserve records of repeated opening and closing of rifts along the zone of Neoarchean sutures and/or along the weak zones. These sedimentary basins, ranging in age from late Palaeoproterozoic through Neoproterozoic are traditionally referred to as Purana basins in Indian literature. The successions of each of the basins may be represented by successive unconformity-bound sequences, which represent several cycles of fluvialshallow marine to shelf-slope-basin sedimentation punctuated by local hiatuses and/or volcanic upheavals. The advance retreat of ancient seaways and their complex are recorded in the sedimentary successions of Purana basins. Papaghni-Chitravati; Kaladgi-Badami; Lower Vindhyan record the oldest cycle of sedimentation. These basins opened after 2.0 Ga and closed by 1.55 Ga. The Chattisgarh and its satellite basins, namely Indravati; Khariar; Ampani opened after the 1.6 Ga. and closed shortly after the 1000 Ma. Albaka; Mallampalli; Kurnool; Bhima preserve Neoproterozoic sedimentation history. The upper Vindhyan basin likely opened after 1.4 Ga. and continued through the Neoproterozoic. The sequence of events indicates a close relationship of craton interior histories with plate tectonics and variations in the heat flow regime underneath the continental crust. Periods of formation of the cratonic basins are coincident with the amalgamation or fragmentation of supercontinents further indicates genetic linkage between the two processes. Synchronous development of the cratonic basins with closely comparable stratigraphy and basin development events, in different small continents, strengthens the view that basin formation processes operated on a global scale, and stratigraphic basin analysis on a regional scale is a significant tool in evaluating the basins’ history. The available stratigraphic, geochronologic or palaeomagnetic data from India is still inadequate, and further information is required to constrain its definite position in the context of global tectonics.
DS202012-2239
2020
Pattanik, J., Demouchy, S., Ghosh, S.Low hydrogen concentrations in Dharwar cratonic lithosphere inferred from peridotites, Wajrakarur kimberlites field: implications for mantle viscosity and carbonated silicate melt metasomatism.Precambrian Research, in press available 15p. PdfIndiadeposit - Wajrakarur

Abstract: Hydrogen as an atomic impurity in mantle minerals is recurrently proposed as a key element impacting significantly on many mantle properties and processes such as melting temperature and mechanical strength. Nevertheless, interpretation based on the natural samples remains weak as we do not have yet a robust world-wild database for hydrogen concentrations in mantle minerals and rocks. Here, we report the first hydrogen concentrations in nominally anhydrous minerals from a rare selection of ultramafic rocks and minerals embedded in Mesoproterozoic Wajrakarur kimberlites (Eastern Dharwar craton, India). Based on key chemical elements, we demonstrate that olivine, pyroxenes and garnet from the Dharwar craton are of mantle origin. We quantify the hydrogen concentrations using Fourier transform infrared spectroscopy (FTIR) and mineral-specific FTIR calibrations. Calculated hydrogen concentrations are, in average, 18 ppm wt H2O in olivine, 70 ppm wt H2O in orthopyroxene and 207 ppm wt H2O in clinopyroxene. Garnet has highly variable hydrogen concentration ranging from 0 to 258 ppm wt H2O, probably influenced by nano-scale inclusions. The average of clean garnet spectra yields 14.5 ppm wt H2O. The reconstructed hydrogen bulk concentrations of Dharwar peridotites yields ppm wt H2O. This value is two to five times lower than the estimated hydrogen concentration in the lithospheric mantle, and agree well with the lower range of hydrogen bulk concentration from the current data base for the upper mantle minerals transported by kimberlites from other cratons (e.g., South Africa, Siberia). The low hydrogen concentration in mantle minerals, together with petrological and geochemical evidence of carbonated silicate melt metasomatism in Dharwar cratonic lithospheric mantle, suggest that these xenoliths are possibly related to proto-kimberlite melts with low water activity prior to being transported to the surface by the Mesoproterozoic Wajrakarur kimberlites. These observations, valid to a depth of ~165-km, suggest that cratonic lithosphere beneath the Dharwar craton may not be particularly indicative of an abnormal hydrogen-rich southern Indian lithosphere in the late Archean and that hydroxylic weakening in olivine would induced a negligible effect on the mantle viscosity of Indian subcontinent.
DS202009-1651
2020
Pattnaik, J., Ghosh, S., Dongre, A.Plume activity and carbonated silicate melt metasomatism in Dharwar cratonic lithosphere: evidence from peridotite xenoliths in Wajrakarur kimberlites.Lithos, in press available, 63p. PdfIndiadeposit - Wajrakarur

Abstract: We report petrography, mineralogy, major- and trace-element compositions of a rare selection of spinel- and garnet-bearing peridotite xenoliths and single crystals separated from peridotites hosted in the Mesoproterozoic Wajrakarur kimberlites from the Eastern Dharwar craton (EDC), India. These ultramafic xenoliths consist of olivine (modal 74-82 vol%) with Fo92-93, clinopyroxene, orthopyroxene, spinel, garnet, and/or ilmenite. Calculated equilibrium pressure and temperature conditions are 2.5-5.0?GPa and 710-1179?°C for these peridotites, which suggests residence depths >160?km near the base of the Dharwar cratonic lithospheric mantle. Garnet in these ultramafic rocks [with Mg#?=?molar (Mg/(Mg?+?Fetotal)?×?100 of 80-88] displays either “sinuous” LREE-enriched patterns with depletion in Gd and Er for harzburgites or “normal” LREE-depleted, HREE-enriched patterns for lherzolites. Two groups of clinopyroxenes (group-I and group-II) were also observed with high LREE (LaN?>?10) and low LREE (LaN?
DS202009-1652
2020
Paul, D., Chandra, J., Halder, M.Proterozoic alkaline rocks and carbonatites of Peninsula India: a review.Episodes, Vol. 43, 1, pp. 249-277.Indiacarbonatites

Abstract: The alkaline rocks and carbonatites (ARCs) of the Great Indian Proterozoic belt bear the testimony of tectonic processes operating in the Proterozoic during the continental assembly and breakup of both Columbia and Rodinia. We present a comprehensive review, mainly focused on the petrology, geochemistry, and geochronology of 38 ARCs of Peninsular India, which are mostly concentrated within the Eastern Ghats Mobile Belt and Southern Granulite Terrain. Available geochronologic data reveals three distinct alkaline magmatic phases (2533-2340 Ma, 1510-1242 Ma, 833-572 Ma) and two metamorphic events (950-930 Ma and 570-485 Ma) that correlate with the Grenvillian and Pan-African orogeny events. Whereas clinopyroxene, amphibole, titanite and apatite fractionation seems to have affected the nephelinite, nepheline syenite and syenite, carbonatite is affected by fractionation of calcite, dolomite, ankerite, pyroxene, apatite, magnetite, mica, and pyrochlore. Trace elements and Sr-Nd-Pb-C-O isotopic compositions of these ARCs strongly suggest a subcontinental lithospheric mantle source, that is enriched either by distribution of subducted crustal material or by metasomatism of mantle-derived fluids, for the generation of ARCs. Despite some isotopic variability that can result from crustal contamination, a trend showing enrichment in 87Sr/86Sri (0.702 to 0.708) and depletion in ?Nd(i) (-1.3 to -14.1) over a 2 Gyr duration indicates temporal changes in the lithospheric/asthenospheric source of ARCs, due to periodic enrichment of the source by mantle-derived fluids. ARC generation starts in an intracontinental rift setting (beginning of Wilson cycle). These early-formed ARCs are carriedto 100 km depths during continental collision (termination stage of Wilson cycle) and undergo extensive melting because of renewed rifting along suture zones to form new generation of ARCs.
DS202002-0214
2020
Paul, J., Ghosh, A.Evolution of cratons through the ages: a time dependent study.Earth and Planetary Science Letters, Vol. 531, 13p. PdfMantlecratons

Abstract: The viscosity of cratons is key to understanding their long term survival. In this study, we present a time-dependent, full spherical, three dimensional mantle convection model to investigate the evolution of cratons of different viscosities. The models are initiated from 409 Ma and run forward in time till the present-day. We impose a surface velocity boundary condition, derived from plate tectonic reconstruction, to drive mantle convection in our models. Cratons of different viscosities evolve accordingly with the changing velocity field from their original locations. Along with the viscosity of cratons, the viscosity of the asthenosphere also plays an important role in cratons' long term survival. Our results predict that for the long-term survival of cratons they need to be at least 100 times more viscous than their surroundings and the asthenosphere needs to have a viscosity of the order of 1020 Pa-s or more.
DS202003-0356
2020
Payne, R.C.Oxidized micrometeorites suggest either high pCO2 or low pN2 during the Neoarchean.Proceedings of the National Academy of Sciences, doi:10.1073/ pnas.1910698117Mantlemeteorites

Abstract: Tomkins et al. [A. G. Tomkins et al., Nature 533, 235-238 (2016)] suggested that iron oxides contained in 2.7-Ga iron micrometeorites can be used to determine the concentration of O2 in the Archean upper atmosphere. Specifically, they argued that the presence of magnetite in these objects implies that O2 must have been near present-day levels (?21%) within the altitude range where the micrometeorites were melted during entry. Here, we reevaluate their data using a 1D photochemical model. We find that atomic oxygen, O, is the most abundant strong oxidant in the upper atmosphere, rather than O2. But data from shock tube experiments suggest that CO2 itself may also serve as the oxidant, in which case micrometeorite oxidation really constrains the CO2/N2 ratio, not the total oxidant abundance. For an atmosphere containing 0.8 bar of N2, like today, the lower limit on the CO2 mixing ratio is ?0.23. This would produce a mean surface temperature of ?300 K at 2.7 Ga, which may be too high, given evidence for glaciation at roughly this time. If pN2 was half the present value, and warming by other greenhouse gases like methane was not a major factor, the mean surface temperature would drop to ?291 K, consistent with glaciation. This suggests that surface pressure in the Neoarchean may need to have been lower—closer to 0.6 bar—for CO2 to have oxidized the micrometeorites. Ultimately, iron micrometeorites may be an indicator for ancient atmospheric CO2 and surface pressure; and could help resolve discrepancies between climate models and existing CO2 proxies such as paleosols.
DS202009-1653
2020
Peacock, S.M.Advances in the thermal and petrologic modeling of subduction zones.Geosphere, Vol. 16, 4, 17p. PdfMantlegeothermometry

Abstract: In the two decades since Subduction: Top to Bottom was published in 1996, improved analytical and numerical thermal-petrologic models of subduction zones have been constructed and evaluated against new seismological and geological observations. Advances in thermal modeling include a range of new approaches to incorporating shear (frictional, viscous) heating along the subduction interface and to simulating induced flow in the mantle wedge. Forearc heat-flux measurements constrain the apparent coefficient of friction (??) along the plate interface to
DS202011-2059
2020
Pearson, G.Diamonds found with gold in Canada's Far North offer clues to Earth's early history: discovery of diamonds in small rock sample hints at possibility of new deposits in area similar to world's richest gold mine in South Africa.www.sciencedaily.com/releases/2020/10/201006153459.htm>., Oct. 6, 3p. Canada, Nunavutdiamond genesis

Abstract: The presence of diamonds in an outcrop atop an unrealized gold deposit in Canada's Far North mirrors the association found above the world's richest gold mine, according to University of Alberta research that fills in blanks about the thermal conditions of Earth's crust three billion years ago.
DS202004-0529
2020
Petrescu, L., Bastow, I.D., Darbyshire, F.A., Gilligan, A., Bodin, T., Menke, W., Levin, V.Three billion years of crustal evolution in eastern Canada: constraints from receiver functions.Journal of Geophysical Research: Solid Earth, in press available, 24p. PdfCanadageophysics - seismics

Abstract: The geological record of SE Canada spans more than 2.5Ga, making it a natural laboratory for the study of crustal formation and evolution over time. We estimate the crustal thickness, Poisson's ratio, a proxy for bulk crustal composition, and shear velocity (Vs) structure from receiver functions at a network of seismograph stations recently deployed across the Archean Superior craton, the Proterozoic Grenville and the Phanerozoic Appalachian provinces. The bulk seismic crustal properties and shear velocity structure reveal a correlation with tectonic provinces of different ages: the post-Archean crust becomes thicker, faster, more heterogenous and more compositionally evolved. This secular variation pattern is consistent with a growing consensus that crustal growth efficiency increased at the end of the Archean. A lack of correlation among elevation, Moho topography, and gravity anomalies within the Proterozoic belt is better explained by buoyant mantle support rather than by compositional variations driven by lower crustal metamorphic reactions. A ubiquitous ?20km thick high-Vs lower-crustal layer is imaged beneath the Proterozoic belt. The strong discontinuity at 20km may represent the signature of extensional collapse of an orogenic plateau, accommodated by lateral crustal flow. Wide anorthosite massifs inferred to fractionate from a mafic mantle source are abundant in Proterozoic geology and are underlain by high Vs lower crust and a gradational Moho. Mafic underplating may have provided a source for these intrusions and could have been an important post-Archean process stimulating mafic crustal growth in a vertical sense.
DS202008-1433
2020
Phani, P.R.C., Lira, R., Espeche, M.J., Reddy, R.A.Geochemical and petrological studies of a magmatic carbonate-bearing metalamprophyre ( spessartite) at Kalagalla - evidence for shoshonitic calc-alkaline magmatism within auriferous Ramagiri-Penakacherla schist belt ( 2.5Ga), eastern Dharwar craton, southGeochimica Brasiensis, Vol. 34, 1, pp. 1-27. pdfIndia, Andhra Pradeshlamprophyres

Abstract: Geochemical and petrological characteristics of lamprophyre dykes at Kalagalla intruded into the auriferous schistose rocks of the Ramagiri- Penakacherla Schist Belt, Anantapur district, Andhra Pradesh, India are presented here. The Kalagalla lamprophyre (KGL) is a melanocratic rock exhibiting typical knobby or pustular texture on the surface. The microtextures and mineralogy typical of lamprophyres are obscured by metamorphism; however, it exhibits porphyritic, nemato-granoblastic texture representative of greenschist facies of metamorphism. The rock is sheared and possesses several globules formed by polycrystalline aggregates of calcite rimmed by coronitic subhedral plagioclase and biotite, evidencing its mantle-magmatic origin. The mineral assemblages noticed in thin-sections include amphibole, plagioclase, biotite, phlogopite and calcite ocelli as essential while apatite, zircon, magnetite, ilmenite, Ni-bearing chalcopyrite and pyrite as accessory phases. The SEM-EDS investigation on the accessory minerals revealed accessory sulphide and silicate phases like As-free pyrite, haematitised Ni-bearing chalcopyrite and Ni-As-Co- minerals indicative of sulphidation associated with greenstone auriferous lodes, along with silicates like LREE-bearing titanite partially transformed into leucoxene and oxide phases like magnetite altered to goethite at places. Based on mineral chemistry, whole rock geochemistry, presence of amphibole and dominance of plagioclase, the KGL is classified as a calc-alkaline variety in general and as spessartite in particular possessing shoshonitic affinity. No anomalous chemical composition is noticed in the ocellar calcite. The LREE-bearing titanite appears to be the contributor of LREE enrichment. The high Mg# (77- 79), Ni (153-162 ppm) and Cr (380-470 ppm) support a mantle source. The absence of Eu anomaly reflects lack of plagioclase fractionation. The high Zr/Hf ratio (163-202) indicates absence of crustal contamination and contribution of magmatic carbonate at the source to form ocelli as product of late-stage liquid silicate-carbonate immiscibility of segregation mechanism. The trace and REE patterns (?REE: 326-343 ppm, LREE>HREE) indicate involvement of residual garnet at the source presumably enriched in phlogopite in a ‘subduction-related’ environment.
DS202007-1170
2020
Phani, R., Sengupta, P., Basu, S.Geochemistry and petrology of two kimberlites at Krishtipadu from Gooty cluster, Andhra Pradesh, southern India - evidence of kimberlite magmatism and a possible carbonate association within Paleoproterozoic lower Cuddapah Basin.Russian Journal of Earth Sciences, Vol. 20, ES3006 14p. PdfIndia, Andhra Pradeshdeposit - Kristipadu

Abstract: This paper addresses geochemical and petrological aspects of two outcropping kimberlites (5023 and 5119) of the Gooty cluster, emplaced in carbonate sediments of Vempalli Formation of lower Cuddapah basin at Krishtipadu, Anantapur district, Andhra Pradesh, southern India. These pipes were discovered by the Rio Tinto Exploration Group in the recent past. The 5023 kimberlite is enriched in olivine and serpentine while the 5119 pipe possesses haematitised olivine pseudomorphs. The field, textural characteristics and whole rock geochemistry qualify both the pipes for hypabyssal kimberlite breccias of Group-I type similar to world’s classical occurrences. The carbon and oxygen stable isotope data, aided with field and petrological studies, indicates existence of possible carbonatite (sovite) phase associated with the 5119 kimberlite. The two kimberlites appear to be originated from a low degree of partial melting ranging from 0.5 to 2.5%. Enrichment of LREE with a high LREE/HREE ratio indicates fractionation at the mantle source region. Whole rock geochemistry supports their diamondiferous nature. Presence of crustal xenoliths post-dates subsequent emplacement of the two pipes to lower Cuddapah sedimentation (2.4 Ga), manifesting kimberlite magmatism. These pipes are the only known Group-I kimberlites from the Proterozoic Cuddapah Basin and therefore warrant detailed investigations. KEYWORDS: Kimberlite; carbonatite; archetypal Group-I; Gooty Kimberlite Cluster; lower Cuddapah basin; stable isotope; Palaeoproterozoic.
DS202010-1866
2020
Piani, L., Marrocchi, Y., Rigaudier, T.Earth's water may have been inherited from material similar to enstatite chondrite metorites.Science, Vol. 369, 6507, pp. 110-1113. doi. 10.1126/ science.aba.1948Mantlewater

Abstract: The abundances of Earth's chemical elements and their isotopic ratios can indicate which materials formed Earth. Enstatite chondrite (EC) meteorites provide a good isotopic match for many elements but are expected to contain no water because they formed in the hot inner Solar System. This would require Earth's water to be from a different source, such as comets. Piani et al. measured hydrogen contents and deuterium/hydrogen ratios (D/H) in 13 EC meteorites (see the Perspective by Peslier). They found far more hydrogen than is commonly assumed, with D/H close to that of Earth's mantle. Combining these data with cosmochemical models, they show that most of Earth's water could have formed from hydrogen delivered by EC meteorites.
DS202012-2240
2020
Pine, D., He, M.Researchers discover novel method for creating colloidal diamonds.Nature, www.sciencetimes.com/ articles/27434/ 20200924Globalnanodiamonds

Abstract: Colloidal diamonds - stable, self-assembled material with promising applications in light-related technologies - can now be fabricated, decades after its concept was first developed in the 90s.
DS202008-1434
2020
Pobric, V., Korolev, N., Kopylova, M.Eclogites of the North Atlantic Craton: insights from Chidliak eclogite xenoliths ( S. Baffin Island, Canada).Contributions to Mineralogy and Petrology, Vol. 175, 8, 25p. PdfCanada, Baffin Islanddeposit - Chidliak

Abstract: The 156-138 Ma Chidliak kimberlites on the Eastern Hall peninsula (EHP) of Baffin Island entrained mantle xenoliths interpreted to have been a part of the Archean North Atlantic Craton (NAC) lithospheric mantle. We studied 19 Chidliak eclogite xenoliths that comprise 10 bimineralic, 5 rutile-bearing, 3 orthopyroxene-bearing and 1 kyanite-bearing eclogites. We report major and trace element compositions of the minerals, calculated bulk compositions, pressures and temperatures of the rock formation and model melt extraction from viable protoliths. The eclogite samples are classified into three groups of HREE-enriched, LREE-depleted and metasomatized based on their reconstructed whole-rock REE patterns. PT parameters of the eclogites were calculated by projecting garnet-clinopyroxene temperatures onto the local P-T arrays for 65 Chidliak peridotite xenoliths. All Chidliak eclogites are equilibrated in the diamond P-T field and cluster in two groups, low-temperature (n?=?5, 840-990 °C at 4.1-5.0 GPa) and high-temperature (n?=?11, T?>?1320 °C at P?>?7.0 GPa). The reconstructed Mg-rich major element bulk compositions and trace elements patterns are similar to Archean basalts from the North Atlantic and Superior cratons and the oceanic gabbros. The LREE-depleted Chidliak eclogites could be residues after 15-55% partial melting of Archean basalt at the eclogite facies of metamorphism that led to extraction of a tonalite-trondhjemite-granodiorite melt from the EHP. The HREE-depleted eclogites may have experienced a lower degree (<10%) of partial melting. Two eclogites may have formed after the gabbro protolith based on the presence of kyanite, high Sr content of garnet and positive Eu anomalies in garnet and bulk eclogite compositions. The metasomatism is reflected in higher Ce/Yb, Sr/Y, TiO2 or MgO of the eclogites. The average contents of MgO, FeO and CaO in NAC eclogites are statistically distinct from those in Slave craton eclogites with a probability of?>95%. The former are more magnesian, less ferrous and calcic, contain more magnesian and less calcic garnets, and lower proportions of group C eclogites. The contrast may relate to the stronger NAC metasomatism by silicate-carbonate melt observed in Chidliak peridotitic mantle, or to the different formation ages of the eclogites beneath the two cratons.
DS202008-1435
2020
Pobric, V., Korolev, N., Kopylova, M.Eclogites of the North Atlantic Craton: insights from Chidliak eclogite xenoliths ( S. Baffin Island, Canada).Goldschmidt 2020, 1p. AbstractCanada, Baffin Islanddeposit - Chidliak
DS202006-0946
2020
Ponomarchuk, V.A., Dobretsov, N.L. , Lazareva, E.V., Zhmodik, S.M., Karmanov, N.S., Tolstov, A,V., Pyryaev, A.N.Evidence of microbial-induced mineralization in rocks of the Tomtor carbonatite complex ( Arctic Siberia).Doklady Earth Science, Vol. 490, 2, pp. 76-80.Russia, Siberiacarbonatite

Abstract: Carbonates of the Tomtor complex of ultramafic alkaline rocks and carbonatites (the northern part of the Republic of Sakha Yakutia) are distinguished by a wide range of carbon isotopic composition ?13C from +2 to -59.9‰. The geological position, localization patterns, mineral and chemical compositions and the relationship with REE mineralization of samples with values of ?13C carbonates from -25 to -59‰ are characterized. The formation of abnormally low ?13C in carbonates is determined by the biogenic oxidation of methane from ?13Cmet to -70‰.
DS202007-1171
2020
Portner, D.E., Rodriguez, E.E., Beck, S., Zandt, G., Scire, A., Rocha, M.P.Detailed structure of the subducted Nazca slab into the lower mantle derived from continent scale teleseismic P wave tomography.Journal of Geophysical Research: Solid Earth, Vol. 125, e2019JB017884.Mantle, South Americasubduction

Abstract: Nazca subduction beneath South America is one of our best modern examples of long?lived ocean?continent subduction on the planet, serving as a foundation for our understanding of subduction processes. Within that framework, persistent heterogeneities at a range of scales in both the South America and Nazca plates is difficult to reconcile without detailed knowledge of the subducted Nazca slab structure. Here we use teleseismic travel time residuals from >1,000 broadband and short?period seismic stations across South America in a single tomographic inversion to produce the highest?resolution contiguous P wave tomography model of the subducting slab and surrounding mantle beneath South America to date. Our model reveals a continuous trench?parallel fast seismic velocity anomaly across the majority of South America that is consistent with the subducting Nazca slab. The imaged anomaly indicates a number of robust features of the subducted slab, including variable slab dip, extensive lower mantle penetration, slab stagnation in the lower mantle, and variable slab amplitude, that are incorporated into a new, comprehensive model of the geometry of the Nazca slab surface to ~1,100 km depth. Lower mantle slab penetration along the entire margin suggests that lower mantle slab anchoring is insufficient to explain along strike upper plate variability while slab stagnation in the lower mantle indicates that the 1,000 km discontinuity is dominant beneath South America.
DS202004-0530
2020
Post, J.E., Feather, R., Butler, J.E.Kimberley diamond acquired by the Smithsonian Institution and its flourescence and phosphorescence characteristics revealed. 55.08 ctJournal of Gemmology, Vol. 37, 1, pp. 14, 15.Africa, South Africa, United Statesflourescence
DS202003-0357
2020
Potter, N.J., Kamenetsky, V.S., Chakhmouradian, A.R., Kamenetsky, M.B., Goemann, K., Rodemann, T.Polymineralic inclusions in oxide minerals of the Afrikanda alkaline ultramafic complex: implications for the evolution of perovskite mineralization.Contributions to Mineralogy and Petrology, Vol. 175, 13p. PdfRussiaperovskite

Abstract: The exceptional accumulation of perovskite in the alkaline-ultramafic Afrikanda complex (Kola Peninsula, Russia) led to the study of polymineralic inclusions hosted in perovskite and magnetite to understand the development of the perovskite-rich zones in the olivinites, clinopyroxenites and silicocarbonatites. The abundance of inclusions varies across the three perovskite textures, with numerous inclusions hosted in the fine-grained equigranular perovskite, fewer inclusions in the coarse-grained interlocked perovskite and rare inclusions in the massive perovskite. A variety of silicate, carbonate, sulphide, phosphate and oxide phases are assembled randomly and in variable proportions in the inclusions. Our observations reveal that the inclusions are not bona fide melt inclusions. We propose that the inclusions represent material trapped during subsolidus sintering of magmatic perovskite. The continuation of the sintering process resulted in the coarsening of inclusion-rich subhedral perovskite into inclusion-poor anhedral and massive perovskite. These findings advocate the importance of inclusion studies for interpreting the origin of oxide minerals and their associated economic deposits and suggest that the formation of large scale accumulations of minerals in other oxide deposits may be a result of annealing of individual disseminated grains.
DS202001-0033
2019
Presser, J.L.B.The diamonds-bearing picritic lamprophyre Ymi-1. ** PORTPyroclastic Flow, Vol. 9, 1, pp. 23-34.South America, Paraguaydeposit - Ymi-1

Abstract: The so-called rift/graben of Asunción was formed in the central-northern portion of the Archon lithospheric nucleus of the Rio de la Plata craton. This structure, related to a crustal thinning, likely resulted from an extraterrestrial impact which produced the San Miguel impact crater. The impact structure is located immediately to the south of the Asunción rift/graben. Within the central E-W segment of the rift/graben and in association with other igneous rocks (potasic to ultra-potasic) of around 130-125 Ma, the picritic rock pipe with lamprofidic texture Ymi-1 occurs. This pipe is found in the lower region of this rift/graben through faults (depths of up to -3000 m). Rocks of a plug and a dike exposed in the pipe Ymi-1 show that it is a strongly porphyritic rock with tendencies of lamprophiric texture formed by micro-feno crystals and mega-crystals of forsteritic olivine (>10 to 30% modal); mega-phenocrysts of Ti-Al diopside and micro-phenocrysts of chromite (Mg-chromite poor in Ti and Mg-Ti chromite); they are supported by an inter-granular matrix formed by aluminosus diopside, Al-Ti-phlogopite/biotite, Mg-Ti-magnetite, amphiboles (hornblends, eckernmanite together with some other potassium to sodic titaniferous amphiboles) accompanied by sanidine, analcime and traces of plagioclase (poor in An molecules). The mineral chemistry of spinels, phlogopites/biotites and diopsids are strongly compatible with mineral chemistry known in calc-alkaline lamprophyres. The rock chemistry of one available dyke is also compatible with the chemistry of calc-alkaline lamprophyres.Ymi-1 is a calc-alkaline picritic lamprophyre pipe where the study of the chromite (50-57 % Cr2O3) type and frosting-tourmaline ("dravites"), obtained in rock and in heavy mineral concentrates (in volcano-epiclastic sediments and in stream sediments -collected in its bed) suggest that it would be a diamond-bearing lamprophyre. The presence of diamonds was confirmed (by X-rays and other methods) in the Ymi-1 pipe. 1D S-wave seismic profile of continental data, for the pipe Ymi-1 site, suggests a geothermal gradient between 38.5 to 39 mW/m2, thus the Ymi-1 calc-alkaline lamprophyre an attractive target for an eventual diamond deposit. Supplementary materials S1 - PDF (Figuras suplementarias) S2 - PDF (Geoquímica mineral) https://pyflow.net/joomla30/index.php/9-all-issues/38-el-lamprofido-picritico-con-diamantes-ymi-1.
DS202010-1867
2020
Presser, J.L.B., Benitez, P.Eclogitic geotherms of the Rio de la Plata craton archon-core: Estancia Trementina and Puentesino, Dpto. Of Concepccion-Paraguay. Compared to two large diamond deposits Argyle ( lamproitic ) and Orapa ( kimberlitic.[email protected], 13p. Pdf 330360071South America, Paraguaygeothermometry
DS202006-0947
2020
Presser, J.L.B., Kumar, S.K. The Bunder lamproites cluster ( India): tectonics, lithospheric mantle and environment - a review.Pyroclastic Flow, Vol. 10, 1, pp. 1-9. pdfIndia, Madhya Pradeshlamproite

Abstract: Bunder diamond-bearing lamproite cluster, located in Madhya Pradesh, India, was discovered in 2004. The Precambrian lamproites are intruding Paleoproterozoic and Mesoproterozoic intracratonic sedimentary rocks covering the Archean Bundelkhand craton. The study of Bundelkhand craton through global dVs% TX2011 model (1D and 2D) led us to recognize that it is underlain by Archean lithospheric mantle as is observed in other locations, in mines with medium to very high diamond-grade (greater than 100 cpht). The Bunder Archean lithospheric mantle has 35 mW/m2 surface heat flow, typical of Archons with pipes with a very high degree of diamonds such as the Argyle lamproite and the kimberlites Internationalnaya, Mir, Ekati, among others. In the Bunder lamproite cluster, the Rio Tinto Exploration estimates for the pipes diamond-grade are below 100 cpht. To understand why Bunder lamproite pipes are low grade in diamonds, we combined comparative gravimetric studies to study the structural architecture model of the crystalline basement. In fact, very-rich diamond pipes develop in different crystalline basement architecture when compared to the pipes discovered in the Bunder cluster; for example the pipe Atri. The pipes next to the Argyle lamproite, the kimberlites pipes International, Mir, Diavik and others were located in the most depressed center of graben/micro graben structures; while the pipe Atri would have positioned on the edges of a graben. It is expected that additional exploration focused on the structural configuration of Bundelkhand craton basement may help to discover new lamproite pipes with a much greater diamond degree than the Bunder cluster.
DS202010-1868
2020
Presser, J.L.B., Monteiro, M., Maldonado, A.Impact diamonds in an extravagant metal piece found in Paraguay. *** PORTHistoria Natural *** english abstract, Vol. 10, 2, 12p. PdfSouth America, Paraguaymeteorite

Abstract: Around 70 km SSE of Chovoreca Hill (Paraguay), a pitcher-like metal piece weighing approximately 303 kg was found. Several studies have been carried out on this piece. Metallographic examination resembles cast iron that presents eutectoid microtextures, but the metal showed Neumann lines. Small fragments of the piece were diluted in concentrated HCl and with this it was possible to obtain colorless crystals, with size ranging from 10 ?m to 1 mm, approximately; SEM/EDS studies showed that major element present is carbon which suggests the presence of diamonds. Raman spectroscopy proved that crystals are diamonds, that showing bands in the “lonsdaleite/diamond zone”, further, the results also showed bands that accuse that the carbon of the diamonds are of meteoritic origin. From the calculus of the FWHM with values around to 42-373 cm-1 centered on 1282 cm-1 peak could be an indication of a very powerful impact that would have formed the diamonds.
DS202007-1172
2020
Prissel, K.B., Krawcznski, M.J., Van Orman, J.A.Fe-Mg and Fe-Mn interdiffusion in ilmenite with implications for geospeedometry using oxides. ( mentions kimberlites)Contributions to Mineralogy and Petrology, Vol. 175, 62 17p. PdfMantleilmenite

Abstract: The Fe-Mg and Fe-Mn interdiffusion coefficients for ilmenite have been determined as a function of temperature and crystallographic orientation. Diffusion annealing experiments were conducted at 1.5 GPa between 800 and 1100 ?C. For Fe-Mg interdiffusion, each diffusion couple consisted of an ilmenite polycrystal and an oriented single crystal of geikielite. The activation energy (Q) and pre-exponential factor (D0) for Fe-Mg diffusion in the ilmenite polycrystal were found to be Q = 188±15 kJ mol?1 and logD0 = ?6.0±0.6 m2 s?1. For the geikielite single crystal, Fe-Mg interdiffusion has Q=220±16 kJ mol?1 and logD0=?4.6±0.7 m2 s?1. Our results indicate that crystallographic orientation did not significantly affect diffusion rates. For Fe-Mn interdiffusion, each diffusion couple consisted of one ilmenite polycrystal and one Mn-bearing ilmenite polycrystal. For Fe-Mn interdiffusion, Q = 264±30 kJ mol?1 and logD0 = ?2.9±1.3 m2 s?1 in the ilmenite. We did not find a significant concentration dependence for the Fe-Mg and Fe-Mn interdiffusion coefficients. In comparing our experimental results for cation diffusion in ilmenite with those previously reported for hematite, we have determined that cation diffusion is faster in ilmenite than in hematite at temperatures <1100 ?C. At oxygen fugacities near the wüstite-magnetite buffer, Fe and Mn diffusion rates are similar for ilmenite and titanomagnetite. We apply these experimentally determined cation diffusion rates to disequilibrium observed in ilmenites from natural volcanic samples to estimate the time between perturbation and eruption for the Bishop Tuff, Fish Canyon Tuff, Mt. Unzen, Mt. St. Helens, and kimberlites. When integrated with natural observations of chemically zoned ilmenite and constraints on pre-eruptive temperature and grain size, our experimentally determined diffusivities for ilmenite can be used to estimate a minimum time between magmatic perturbation and eruption on the timescale of hours to months.
DS202008-1436
2020
Prokopyev, I.R., Kozlov, E., Fomina,E., Doroshkevich, A.Mineralogy and fluid regime of formation of the REE-Late-Stage hydrothermal mineralization of Petyayan-Vara carbonatites ( Vuoriyarvi, Kola region, NW Russia.Minerals, 19p. PdfRussia, Kola Peninsulacarbonatite

Abstract: The Vuoriyarvi Devonian alkaline-ultramafic complex (northwest Russia) contains magnesiocarbonatites with rare earth mineralization localized in the Petyayan-Vara area. High concentrations of rare earth elements are found in two types of these rocks: (a) ancylite-dominant magnesiocarbonatites with ancylite-baryte-strontianite-calcite-quartz (±late Ca-Fe-Mg carbonates) ore assemblage, i.e., “ancylite ores”; (b) breccias of magnesiocarbonatites with a quartz-bastnäsite matrix (±late Ca-Fe-Mg carbonates), i.e., “bastnäsite ores.” We studied fluid inclusions in quartz and late-stage Ca-Fe-Mg carbonates from these ore assemblages. Fluid inclusion data show that ore-related mineralization was formed in several stages. We propose the following TX evolution scheme for ore-related processes: (1) the formation of ancylite ores began under the influence of highly concentrated (>50 wt.%) sulphate fluids (with thenardite and anhydrite predominant in the daughter phases of inclusions) at a temperature above300-350 °C; (2) the completion of the formation of ancylite ores and their auto-metasomatic alteration occurred under the influence of concentrated (40-45 wt.%) carbonate fluids (shortite and synchysite-Ce in fluid inclusions) at a temperature above 250-275 °C; (3) bastnäsite ores deposited from low-concentrated (20-30 wt.%) hydrocarbonate-chloride fluids (halite, nahcolite, and/or gaylussite in fluid inclusions) at a temperature of 190-250 °C or higher. Later hydrothermal mineralization was related to the low-concentration hydrocarbonate-chloride fluids (<15 wt.% NaCl-equ.) at 150-200 °C. The presented data show the specific features of the mineral and fluid evolution of ore-related late-stage hydrothermal rare earth element (REE) mineralization of the Vuoriyarvi alkaline-ultramafic complex.
DS202012-2241
2020
Pujol-Sola, N.Diamond forms during low pressure serpentinization of oceanic lithosphere.Geochemical perspective Letters, Globalnanodiamonds

Abstract: Diamond is commonly regarded as an indicator of ultra-high pressure conditions in Earth System Science. This canonical view is challenged by recent data and interpretations that suggest metastable growth of diamond in low pressure environments. One such environment is serpentinisation of oceanic lithosphere, which produces highly reduced CH4-bearing fluids after olivine alteration by reaction with infiltrating fluids. Here we report the first ever observed in situ diamond within olivine-hosted, CH4-rich fluid inclusions from low pressure oceanic gabbro and chromitite samples from the Moa-Baracoa ophiolitic massif, eastern Cuba. Diamond is encapsulated in voids below the polished mineral surface forming a typical serpentinisation array, with methane, serpentine and magnetite, providing definitive evidence for its metastable growth upon low temperature and low pressure alteration of oceanic lithosphere and super-reduction of infiltrated fluids. Thermodynamic modelling of the observed solid and fluid assemblage at a reference P-T point appropriate for serpentinisation (350 °C and 100 MPa) is consistent with extreme reduction of the fluid to logfO2 (MPa) = ?45.3 (?logfO2[Iron-Magnetite] = ?6.5). These findings imply that the formation of metastable diamond at low pressure in serpentinised olivine is a widespread process in modern and ancient oceanic lithosphere, questioning a generalised ultra-high pressure origin for ophiolitic diamond.
DS202010-1869
2020
Pujol-Sola, N., Garcia-Casco, A., Proenza, J.A., Gonzalez-Jiminez, J.M., del Camp, A., Colas, V., Canals, A., Sanchez-Navas, A., Roque-Rosell, J.Diamond forms during low pressure serpentinisation of oceanic lithosphere.Geochemical Perspectives Letters, 7p. PdfCentral America, Cubadiamond genesis

Abstract: Diamond is commonly regarded as an indicator of ultra-high pressure conditions in Earth System Science. This canonical view is challenged by recent data and interpretations that suggest metastable growth of diamond in low pressure environments. One such environment is serpentinisation of oceanic lithosphere, which produces highly reduced CH4-bearing fluids after olivine alteration by reaction with infiltrating fluids. Here we report the first ever observed in situ diamond within olivine-hosted, CH4-rich fluid inclusions from low pressure oceanic gabbro and chromitite samples from the Moa-Baracoa ophiolitic massif, eastern Cuba. Diamond is encapsulated in voids below the polished mineral surface forming a typical serpentinisation array, with methane, serpentine and magnetite, providing definitive evidence for its metastable growth upon low temperature and low pressure alteration of oceanic lithosphere and super-reduction of infiltrated fluids. Thermodynamic modelling of the observed solid and fluid assemblage at a reference P-T point appropriate for serpentinisation (350 °C and 100 MPa) is consistent with extreme reduction of the fluid to logfO2 (MPa) = ?45.3 (?logfO2[Iron-Magnetite] = ?6.5). These findings imply that the formation of metastable diamond at low pressure in serpentinised olivine is a widespread process in modern and ancient oceanic lithosphere, questioning a generalised ultra-high pressure origin for ophiolitic diamond.
DS202012-2242
2020
Qin, L., Yang, C.Magnetotelluric soundings on a stratified Earth with two transitional layers.Pure and Applied Physics, Vol. 177, pp. 5263-5274.Mantlegeophysics - magnetics

Abstract: Theoretical magnetotelluric (MT) soundings are investigated for a stratified (five-layered) Earth model consisting of two transitional layers with conductivity varying linearly with depth, and three homogeneous layers with constant conductivity. The analytical expressions for the tangential electric and magnetic fields as well as the surface impedance are derived in terms of Airy functions. The effect of the thicknesses of the two transitional layers and the interlayer between them on the MT responses (apparent resistivity and impedance phase) is examined in detail.
DS202010-1870
2020
Rama Rao, J.V., Kumar, B.R., Kumar, M., Singh, R.B., Veeraich, B.Gravity of Dharwar craton, southern Indian shield.Journal of Geological Society of India, Vol. 96, 3, pp. 239-249. pdfIndiacraton

Abstract: Dharwar craton (DC), by far the largest geological domain in South Indian Shield, occupying about 0.5 million sq. km area, is well-studied terrain both for regional geoscientific aspects and as part of mineral exploration over several important blocks such as the greenstone belts, ultramafic complexes, granite-gneissic terrain and the Proterozoic sediments of Cuddapah basin. The re-look into regional gravity data offers several insights into nature of crust, sub-divisions within the craton, bedrock geology in the covered areas and mineral potentiality of this ancient and stable crust. The regional gravity profiles drawn across the south Indian region mainly suggest that the area can be divided into five domains as Western Dharwar craton (WDC), Central Dharwar craton (CDC), Eastern Dharwar craton (EDC 1), transitory zone of EDC (EDC 2) and Eastern Ghats mobile belt (EGMB) areas. The Bouguer gravity anomaly pattern also questions some of the earlier divisions like eastern margin of Chitradurga schist belt between the WDC and EDC and the boundary of DC with southern granulite terrain (SGT) as they do not restrict at these main boundaries. In this study, mainly four issues are addressed by qualitative and quantitative analysis of regional gravity data and those revealed significant inferences. (1) A distinct gravity character in central part of south Indian shield area occupying about 60, 000 sq. km, suggests that the transitory crustal block, faulted on both sides and uplifted. This area designated as central Dharwar craton (CDC) is characterized with schist belts having characters of both parts of western and eastern Dharwar craton. This inference also opens up the debate about the boundary between western and eastern parts of the craton. Another significant inference is the extension of major schist belts beneath both Deccan volcanic province (DVP) in northwestern part and Cuddapah basin (CB) in southeastern part. (2) Eastern Dharwar craton is reflected as two distinct domains of different gravity characters; one populated with number of circular gravity lows and a few linear gravity high closures indicative of plutonic and volcanic activity and another domain devoid of these intrusive younger granites or schist belts. (3) Large wave length gravity highs occupying thousands of sq.km area and those not relatable to surface geology in eastern Dharwar craton that may have significance for mineral exploration. (4) Gravity data was subjected to further processing like two dimensional modeling which have yielded insights into crustal architecture beneath the Dharwar craton, crustal scale lineaments, craton-mobile belt contact zone and younger intrusives.
DS202003-0358
2019
Rameshchandra Phani, P.Restoring the past glory of diamond mining in south India - A plausible case of diamondiferous Wajrakarur kimberlite pipe clusters with geochemical evidences.International Journal of Mining and Geo-Engineering, 11p. PdfIndiadeposit - Wajrakarur

Abstract: A plausible case of collective and economical mining of diamondiferous kimberlite deposits of Wajrakarur and adjoining places in Andhra Pradesh, southern India along with the whole-rock geochemical evidences in support of their diamond potentiality are discussed in this article. The kimberlites/lamproites are mantle-derived ultrabasic rocks which rarely carry diamonds from mantle to the earth’s surface through carrot-shaped intrusions referred to as pipes. Even though few hundreds of diamondiferous kimberlite pipes were discovered in India so far, there is no other production unit than Panna diamond mine in the country where primary rock is mined. In ancient India, diamond mining in south India in the Krishna river valley was well-known to the world fascinated by famous gemstones like Koh-I-Noor, Hope, Darya-e-Noor, Noor-ul-ain etc. which were mainly extracted from alluvium or colluvium in Krishna river valley. Having bestowed with more than 45 kimberlite pipes, the Wajrakarur kimberlite field (WKF) forms a favourable region for initiating diamond mining in the country. Geochemically, majority of the WKF show low TiO2 content and considerably high diamond grade (DG) values (>3) except some pipes viz., P-5 (Muligiripalli), P-13 (Tummatapalli) and P-16 (Pennahobilam) are barren due to high TiO2 and ilmenite contents. The TiO2 content (0.66-6.62 wt%) is inversely proportional to the DG (3.33 to 22.13). The DG value of some of the WKF pipes is close to that of Panna (8.36). The cationic weight% values clearly portray the diamondiferous nature of these deposits. The WKF pipes were also proved to be diamondiferous by exploratory drilling and bulk sample processing results by the government organisations. In southern India, due to several reasons, diamond mining has not seen its initiation and impetus till now although it records a considerable number of fertile kimberlite pipes at Wajrakarur, Lattavaram, Chigicherla, Timmasamudram etc. Though the majority of WKF diamondiferous kimberlite deposits in Wajrakarur are small in their areal extent (0.06-4.48 Ha) some of them are large (>10 Ha up to 120 ha). They occur in close proximity to each other offering feasibility for collective mining and winning the precious stone through a central processing unit by deploying the latest processing technologies. The geographic conditions of this region such as availability of human resources, water resources, vast open lands, wind power generation etc. also support to initiate mining of kimberlite pipes in this area. The availability of rough diamonds produced from local mines will make the polishing industry to meet its business needs during circumstances of the shortage of rough stone influx from foreign. Hence, although it demands liberal investments, reviving diamond mining in southern India can be materialised with a meticulous evaluation of these deposits ascertaining profitability. This will certainly help to restore the past glory of diamond mining in the southern part of the subcontinent.
DS202001-0034
2019
Ramstein, G., Godderis, Y., Donnadieu, Y., Sepulchre, P., Fluteau, F., Zhang, Z., Zhang, R., Su, B., Jiang, D., Schuster, M., Besse, J.Some illustrations of large tectonically driven climate changes in Earth history.Tectonics, doi.org/10.1029/ 2019TC005569Mantletectonics

Abstract: For the celebration of the 50th anniversary of the publication of the pioneering papers that established the basis of plate tectonic, this paper was solicited to illustrate the close relation between tectonics and climate. Amongst the large spectrum of interactions that depict how tectonics modified the climate at geological time steps, we choose to illustrate two major issues: (1) How the “tryptic” climate/long?term carbon cycle/tectonics explains the extraordinary glacial episode (717-635 Ma) occurring during Neoproterozoic era? (2) How major tectonic events (i.e., the slow shrinkage of a huge epicontinental sea and the uplift of large mountains ranges in Asia and Africa) drastically changed the climate and shaped the pattern of present?day monsoons systems. This paper is the result of long?standing collaboration with many researchers from different countries.
DS202010-1871
2020
Rebeiro, B.V., Cawood, P.A., Faleiros, F.M., Mulder, J.A., Martin, E., Finch, M.A., Raveggi, M., Teixeira, W., Cordani, U.G., Pavan, M.A long lived active margin revealed by zircon U-Pb-Hf data from the Rio Apa terrane (Brazil): new insights into the Paleoproterozoic evolution of the Amazonian craton.Precambrian Research, 57p. PdfSouth America, Brazilcraton

Abstract: We present the first regional in-situ zircon U-Pb-Hf isotopic data from metaigneous and metasedimentary rocks from the Paleo- to Mesoproterozoic Rio Apa Terrane (RAT), a crustal fragment outcropping in the central-western Brazil and north-eastern Paraguay. These new ages and Hf isotopic data delineate three magmatic events, which record the construction of the temporally and isotopically distinct Western and Eastern Terranes of the RAT. The Western Terrane comprises the 2100-1940 Ma Porto Murtinho Complex and the 1900-1840 Ma Amoguijá Belt, which both define a crustal reworking array in ?HfT-time space evolving from a precursor source with Hf TDM age of ca. 2700 Ma. The 1800-1720 Ma Caracol Belt constitutes the Eastern Terrane and yields suprachondritic ?HfT signatures up to +7.1, indicating significant juvenile input. The metasedimentary Amolar Group and Rio Naitaca Formation in the Western Terrane have maximum depositional ages of 1850-1800 Ma and subchondritic ?HfT signatures down to ?5.7, similar to the underlying basement of the Amoguijá Belt. In the Eastern Terrane, the Alto Tererê Formation has a maximum depositional age of 1750 Ma and mostly suprachondritic ?HfT signatures, similar to magmatic rocks of the underlying Caracol Belt. Together, the new igneous and detrital zircon age and Hf isotopic data record a temporal and spatial transition from 2100 to 1840 Ma crustal reworking in the west to more juvenile magmatism at 1800-1720 Ma in the east. This transition is interpreted to reflect convergent margin magmatism associated with periods of subduction zone advance and retreat in an accretionary orogenic setting. Comparison of the ?HfT-time signature of the RAT with the Amazonian Craton suggest penecontemporaneous development, with the Western and Eastern Terranes of the RAT being correlative with the Ventuari-Tapajós and Rio Negro-Juruena Province of the Amazonian Craton, respectively. Our new data also reveal that the ?HfT signatures of the RAT are distinct from the Maz terrane, which refutes the MARA Block hypothesis.
DS202012-2243
2020
Regier, M. Distinct diamond forming mechanisms in the lithosphere, asthenosphere, and lower mantle.https://www.youtube. com/channel/ UCcZvayDnqD DazIHAh1Otreg, Nov 3 ppt presenation ( see also her paper in Nature previously listed in Newsletter)Mantlediamond genesis. Cratons

Abstract: November 2020 Vancouver Kimberlite Cluster presentation. 'Superdeep' diamonds from the sublithospheric mantle (greater than 250 km in depth) comprise some of the most highly-priced samples in kimberlitic diamond deposits. These superdeep diamonds are distinguished from their more common lithospheric diamonds cousins by their large sizes, highly resorbed morphologies, and characteristic inclusion assemblages. Despite these defining characteristics, our understanding of superdeep diamond formation remains limited. How exactly does diamond formation differ between the upper and lower mantle? In this presentation, I will discuss how stable isotopic analyses of lithospheric to lower mantle diamonds can elucidate the various diamond forming mechanisms that operate at these depths. I will show evidence for diamond-forming carbonate-rich magmas in the transition zone and will illustrate how the final dehydration of slabs may remobilize carbon trapped in metallic phases in the lower mantle.
DS202010-1872
2020
Regier, M.E., Pearson, D.G., Stachel, T., Luth, R.W., Stern, R.A., Harris, J.W.The lithospheric-to-lower-mantle carbon cycle recorded in superdeep diamonds. ( Kankan)Nature, Vol. 585, pp. 234-238. pdfAfrica, Guineadiamond inclusions

Abstract: The transport of carbon into Earth’s mantle is a critical pathway in Earth’s carbon cycle, affecting both the climate and the redox conditions of the surface and mantle. The largest unconstrained variables in this cycle are the depths to which carbon in sediments and altered oceanic crust can be subducted and the relative contributions of these reservoirs to the sequestration of carbon in the deep mantle1. Mineral inclusions in sublithospheric, or ‘superdeep’, diamonds (derived from depths greater than 250 kilometres) can be used to constrain these variables. Here we present oxygen isotope measurements of mineral inclusions within diamonds from Kankan, Guinea that are derived from depths extending from the lithosphere to the lower mantle (greater than 660 kilometres). These data, combined with the carbon and nitrogen isotope contents of the diamonds, indicate that carbonated igneous oceanic crust, not sediment, is the primary carbon-bearing reservoir in slabs subducted to deep-lithospheric and transition-zone depths (less than 660 kilometres). Within this depth regime, sublithospheric inclusions are distinctly enriched in 18O relative to eclogitic lithospheric inclusions derived from crustal protoliths. The increased 18O content of these sublithospheric inclusions results from their crystallization from melts of carbonate-rich subducted oceanic crust. In contrast, lower-mantle mineral inclusions and their host diamonds (deeper than 660 kilometres) have a narrow range of isotopic values that are typical of mantle that has experienced little or no crustal interaction. Because carbon is hosted in metals, rather than in diamond, in the reduced, volatile-poor lower mantle2, carbon must be mobilized and concentrated to form lower-mantle diamonds. Our data support a model in which the hydration of the uppermost lower mantle by subducted oceanic lithosphere destabilizes carbon-bearing metals to form diamond, without disturbing the ambient-mantle stable-isotope signatures. This transition from carbonate slab melting in the transition zone to slab dehydration in the lower mantle supports a lower-mantle barrier for carbon subduction.
DS202001-0035
2019
Reina, G., Zhao, Li. Bianco, A., Komatsu, N.Chemical functionalization of nanodiamonds: opportunities and challenges ahead.Angewandte Chemie International edition, Vol. 58, 50, pp. 17918-17929.Globalnanodiamond

Abstract: Nanodiamond(ND)?based technologies are flourishing in a wide variety of fields spanning from electronics and optics to biomedicine. NDs are considered a family of nanomaterials with an sp3 carbon core and a variety of sizes, shapes, and surfaces. They show interesting physicochemical properties such as hardness, stiffness, and chemical stability. Additionally, they can undergo ad?hoc core and surface functionalization, which tailors them for the desired applications. Noteworthy, the properties of NDs and their surface chemistry are highly dependent on the synthetic method used to prepare them. In this Minireview, we describe the preparation of NDs from the materials?chemistry viewpoint. The different methodologies of synthesis, purification, and surface functionalization as well as biomedical applications are critically discussed. New synthetic approaches as well as limits and obstacles of NDs are presented and analyzed.
DS202012-2244
2020
Reuber, G.S., Simons, F.J.Multi-physics adjoint modeling of Earth structure: combining gravimetric, seismic, and geodynamic inversions.GEM: International Journal on Geomathematics, open access 38p. PdfMantlegeophysics - magnetics

Abstract: We discuss the resolving power of three geophysical imaging and inversion techniques, and their combination, for the reconstruction of material parameters in the Earth’s subsurface. The governing equations are those of Newton and Poisson for gravitational problems, the acoustic wave equation under Hookean elasticity for seismology, and the geodynamics equations of Stokes for incompressible steady-state flow in the mantle. The observables are the gravitational potential, the seismic displacement, and the surface velocity, all measured at the surface. The inversion parameters of interest are the mass density, the acoustic wave speed, and the viscosity. These systems of partial differential equations and their adjoints were implemented in a single Python code using the finite-element library FeNICS. To investigate the shape of the cost functions, we present a grid search in the parameter space for three end-member geological settings: a falling block, a subduction zone, and a mantle plume. The performance of a gradient-based inversion for each single observable separately, and in combination, is presented. We furthermore investigate the performance of a shape-optimizing inverse method, when the material is known, and an inversion that inverts for the material parameters of an anomaly with known shape.
DS202004-0531
2020
Rezvukhin, D.I., Alifirova, T.A., Golovin, A.V., Korsakov, A.V.A plethora of epigenetic minerals reveals a multistage metasomatic overprint of a mantle orthopyroxenite from the Udachaya kimberlite.Minerals MDPI, Vol. 10, 10030264. 34p. PdfRussiadeposit - Udachnaya

Abstract: More than forty mineral species of epigenetic origin have been identified in an orthopyroxenite from the Udachnaya-East kimberlite pipe, Daldyn kimberlite field, Siberian platform. Epigenetic phases occur as: (1) Mineral inclusions in the rock-forming enstatite, (2) daughter minerals within large (up to 2 mm) crystallized melt inclusions (CMI) in the rock-forming enstatite, and (3) individual grains and intergrowths in the intergranular space of the xenolith. The studied minerals include silicates (olivine, clinopyroxene, phlogopite, tetraferriphlogopite, amphibole-supergroup minerals, serpentine-group minerals, talc), oxides (several generations of ilmenite and spinel, rutile, perovskite, rare titanates of the crichtonite, magnetoplumbite and hollandite groups), carbonates (calcite, dolomite), sulfides (pentlandite, djerfisherite, pyrrhotite), sulfate (barite), phosphates (apatite and phosphate with a suggested crystal-chemical formula Na2BaMg[PO4]2), oxyhydroxide (goethite), and hydroxyhalides (kuliginite, iowaite). The examined epigenetic minerals are interpreted to have crystallized at different time spans after the formation of the host rock. The genesis of minerals is ascribed to a series of processes metasomatically superimposed onto the orthopyroxenite, i.e., deep-seated mantle metasomatism, infiltration of a kimberlite-related melt and late post-emplacement hydrothermal alterations. The reaction of orthopyroxene with the kimberlite-related melt has led to orthopyroxene dissolution and formation of the CMI, the latter being surrounded by complex reaction zones and containing zoned olivine grains with extremely high-Mg# (up to 99) cores. This report highlights the utility of minerals present in minor volume proportions in deciphering the evolution and modification of mantle fragments sampled by kimberlitic and other deep-sourced magmas. The obtained results further imply that the whole-rock geochemical analyses of mantle-derived samples should be treated with care due to possible drastic contaminations from “hiding” minor phases of epigenetic origin.
DS202008-1437
2020
Rezvukhin, D.I., Alifirova, T.A., Golovin, A.V., Korsakov, A.V.A plethora of epigenetic minerals reveals a multistage metasomatic overprint of a mantle orthopyroxenite from the Udachnaya kimberlite.MDPI Minerals, Vol. 10, 264, doi.10.3390/ min10030264 34p. PdfRussiadeposit - Udachnaya-East

Abstract: More than forty mineral species of epigenetic origin have been identified in an orthopyroxenite from the Udachnaya-East kimberlite pipe, Daldyn kimberlite field, Siberian platform. Epigenetic phases occur as: (1) Mineral inclusions in the rock-forming enstatite, (2) daughter minerals within large (up to 2 mm) crystallized melt inclusions (CMI) in the rock-forming enstatite, and (3) individual grains and intergrowths in the intergranular space of the xenolith. The studied minerals include silicates (olivine, clinopyroxene, phlogopite, tetraferriphlogopite, amphibole-supergroup minerals, serpentine-group minerals, talc), oxides (several generations of ilmenite and spinel, rutile, perovskite, rare titanates of the crichtonite, magnetoplumbite and hollandite groups), carbonates (calcite, dolomite), sulfides (pentlandite, djerfisherite, pyrrhotite), sulfate (barite), phosphates (apatite and phosphate with a suggested crystal-chemical formula Na2BaMg[PO4]2), oxyhydroxide (goethite), and hydroxyhalides (kuliginite, iowaite). The examined epigenetic minerals are interpreted to have crystallized at different time spans after the formation of the host rock. The genesis of minerals is ascribed to a series of processes metasomatically superimposed onto the orthopyroxenite, i.e., deep-seated mantle metasomatism, infiltration of a kimberlite-related melt and late post-emplacement hydrothermal alterations. The reaction of orthopyroxene with the kimberlite-related melt has led to orthopyroxene dissolution and formation of the CMI, the latter being surrounded by complex reaction zones and containing zoned olivine grains with extremely high-Mg# (up to 99) cores. This report highlights the utility of minerals present in minor volume proportions in deciphering the evolution and modification of mantle fragments sampled by kimberlitic and other deep-sourced magmas. The obtained results further imply that the whole-rock geochemical analyses of mantle-derived samples should be treated with care due to possible drastic contaminations from “hiding” minor phases of epigenetic origin.
DS202008-1438
2019
Rezvukhina, O.V., Korsakov, A.V., Rezvukin, D.I., Zamyatin, D.A., Zelenovskiy, P.S., Greshnyakov, E.D., Shur, V.Y.A combined Raman spectroscopy, cathodoluminescence, and electron backscatter diffraction study of kyanite porphyroblasts from diamondiferous and diamond-free metamorphic rocks ( Kokchetav Massif).Journal of Raman Spectroscopy, 13p. PdfRussialuminescence

Abstract: A series of precise nondestructive analytical methods (Raman spectroscopy, cathodoluminescence, and EBSD—electron backscatter diffraction) has been employed to investigate the internal textures of kyanite porphyroblasts from diamondiferous and diamond?free ultrahigh?pressure metamorphic rocks (Kokchetav massif, Northern Kazakhstan). Such internal kyanite characteristics as twinning, radial fibrous pattern, and spotty zoning were identified by means of Raman and cathodoluminescence imaging, whereas an intergrowth of two kyanite crystals was distinguished only by Raman imaging. The EBSD analysis recorded an ~10-25° changing of orientations along the elongation in the investigated kyanite porphyroblasts. The absence of a radial fibrous pattern and a spotty zoning on the EBSD maps indicates that these textures are not related to variations in crystallographic orientation. The absence of clear zoning patterns (cores, mantles, and rims) on the Raman, cathodoluminescence, or EBSD maps of the kyanite porphyroblasts indicates the rapid single?stage formation of these porphyroblasts near the peak metamorphic conditions and the lack of recrystallization processes. The obtained results provide important implications for deciphering of mineral internal textures, showing that the data obtained by cathodoluminescence mapping can be clearly reproduced by Raman imaging, with the latter method occasionally being even more informative. This observation is of significant importance for the study of minerals that are unexposed on a thin section surface or Fe? and Ni?rich minerals that do not show luminescence emission. The combination of the Raman spectroscopic, cathodoluminescence, and EBSD techniques may provide better spatial resolution for distinguishing different domains and textural peculiarities of mineral than the selective application of individual approaches.
DS202001-0036
2019
Rimmer, A.When British based company Opsydia established to "disrupt a number of industries by its ability to create invisible structures inside transparent materials" the implications for diamond security and identification were a tantalising route to market.Gems & Jewellery, Vol. 28, 4, pp. 28-29.Europe, United KingdomOpsydia
DS202005-0758
2020
Ritsema, J., Lekic, V.Heterogeneity of seismic wave velocity in Earth's mantle.Annual Review of Earth and Planetary Sciences, Vol.48, 25p. PdfMantlegeophysics - seismics

Abstract: Seismology provides important constraints on the structure and dynamics of the deep mantle. Computational and methodological advances in the past two decades improved tomographic imaging of the mantle and revealed the fine-scale structure of plumes ascending from the core-mantle boundary region and slabs of oceanic lithosphere sinking into the lower mantle. We discuss the modeling aspects of global tomography including theoretical approximations, data selection, and model fidelity and resolution. Using spectral, principal component, and cluster analyses, we highlight the robust patterns of seismic heterogeneity, which inform us of flow in the mantle, the history of plate motions, and potential compositionally distinct reservoirs. In closing, we emphasize that data mining of vast collections of seismic waveforms and new data from distributed acoustic sensing, autonomous hydrophones, ocean-bottom seismometers, and correlation-based techniques will boost the development of the next generation of global models of density, seismic velocity, and attenuation. Seismic tomography reveals the 100-km to 1,000-km scale variation of seismic velocity heterogeneity in the mantle. Tomographic images are the most important geophysical constraints on mantle circulation and evolution.
DS202007-1173
2020
Ritsema, J., Lekic, V.Heterogeneity of seismic wave velocity in Earth's mantle.Annual Review of Earth and Planetary Sciences, Vol. 48, 1, pp. w77-401.Mantlegeophysics - seismics

Abstract: Seismology provides important constraints on the structure and dynamics of the deep mantle. Computational and methodological advances in the past two decades improved tomographic imaging of the mantle and revealed the fine-scale structure of plumes ascending from the core-mantle boundary region and slabs of oceanic lithosphere sinking into the lower mantle. We discuss the modeling aspects of global tomography including theoretical approximations, data selection, and model fidelity and resolution. Using spectral, principal component, and cluster analyses, we highlight the robust patterns of seismic heterogeneity, which inform us of flow in the mantle, the history of plate motions, and potential compositionally distinct reservoirs. In closing, we emphasize that datamining of vast collections of seismic waveforms and new data from distributed acoustic sensing, autonomous hydrophones, ocean-bottom seismometers, and correlation-based techniques will boost the development of the next generation of global models of density, seismic velocity, and attenuation.
DS202002-0215
2020
Ritter, X., Sanchez-Valle, C., Sator, N., Desmaele, E., Guignot, N., King, A., Kupenko, I., Berndt, J., Guillot, B.Density of hydrous carbonate melts under pressure, compressability of volatiles and implications for carbonate melt mobility in the upper mantle.Earth and Planetary Science Letters, Vol. 533, 11p. PdfMantlecarbon

Abstract: Knowledge of the effect of water on the density of carbonate melts is fundamental to constrain their mobility in the Earth's interior and the exchanges of carbon between deep and surficial reservoirs. Here we determine the density of hydrous MgCO3 and CaMg(CO3)2 melts (10 wt% H2O) from 1.09 to 2.98 GPa and 1111 to 1763 K by the X-ray absorption method in a Paris-Edinburgh press and report the first equations of state for hydrous carbonate melts at high pressure. Densities range from 2.26(3) to 2.50(3) g/cm3 and from 2.34(3) to 2.48(3) g/cm3 for hydrous MgCO3 and CaMg(CO3)2 melts, respectively. Combining the results with density data for the dry counterparts from classical Molecular Dynamic (MD) simulations, we derive the partial molar volume (, ) and compressibility of H2O and CO2 components at crustal and upper mantle conditions. Our results show that in alkaline carbonate melts is larger and less compressible than at the investigated conditions. Neither the compressibility nor depend on carbonate melt composition within uncertainties, but they are larger than those in silicate melts at crustal conditions. in alkaline earth carbonate melts decreases from 25(1) to 16.5(5) cm3/mol between 0.5 and 4 GPa at 1500 K. Contrastingly, comparison of our results with literature data suggests strong compositional effects on , that is also less compressible than in transitional melts (e.g., kimberlites) and carbonated basalts. We further quantify the effect of hydration on the mobility of carbonate melts in the upper mantle and demonstrate that 10 wt% H2O increases the mobility of MgCO3 melts from 37 to 67 g.cm?3.Pa?1s?1 at 120 km depth. These results suggest efficient carbonate melt extraction during partial melting and fast migration of incipient melts in the shallow upper mantle.
DS202009-1654
2020
Ritterbex, S., Carrez, P., Cordier, P.Deformation across the mantle transition zone: a theoretical mineral physics view.Earth and Planetary Science Letters, Vol. 547, 10p. PdfMantleWadsleyite, ringwoodite, majorite garnet

Abstract: The dynamics of the Earth's mantle is still poorly constrained due to the lack of understanding the transfer of matter between the upper and the lower mantle and their convective vigor. The transition zone (TZ) might play a crucial role as the interface connecting the upper to the lower mantle. Here, we examine the rheology of the main TZ minerals, wadsleyite, ringwoodite and majorite garnet based on a mineral physics approach. Using the results of lattice friction modeling and dislocation glide mobilities together with the available data on self-diffusion in the TZ minerals, we quantify their plastic deformation by diffusion and dislocation creep from theoretical plasticity models. We show that pure climb creep is expected to contribute to the plasticity of the TZ without the need of significant diffusion-related hydrolytic weakening, matching well the geophysical observations. Our model results predict that crystallographic preferred orientations (CPO) might only develop along with stress concentrations as present around cold subducting slabs which can be locally weaker than the surrounding TZ despite their lower temperatures.
DS202012-2245
2020
Ritterbex, S., Carrez, P., Cordier, P.Deformation across the mantle transition zone: a theoretical mineral physics view.Earth and Planetary Letters, Vol. 547, 116438, 10p. PdfMantlewadsleyite

Abstract: The dynamics of the Earth's mantle is still poorly constrained due to the lack of understanding the transfer of matter between the upper and the lower mantle and their convective vigor. The transition zone (TZ) might play a crucial role as the interface connecting the upper to the lower mantle. Here, we examine the rheology of the main TZ minerals, wadsleyite, ringwoodite and majorite garnet based on a mineral physics approach. Using the results of lattice friction modeling and dislocation glide mobilities together with the available data on self-diffusion in the TZ minerals, we quantify their plastic deformation by diffusion and dislocation creep from theoretical plasticity models. We show that pure climb creep is expected to contribute to the plasticity of the TZ without the need of significant diffusion-related hydrolytic weakening, matching well the geophysical observations. Our model results predict that crystallographic preferred orientations (CPO) might only develop along with stress concentrations as present around cold subducting slabs which can be locally weaker than the surrounding TZ despite their lower temperatures.
DS202012-2246
2020
Rogov, Y., Kremenets, V., Sapozhnikov, M., Sebele, M.Application of tagged neutron method for detecting diamonds in kimberlite.Instruments, Vol. 4, 4, doi.org/103390/ instruments4040033Globalneutron technology

Abstract: The results of testing a prototype of a separator for detecting diamonds in kimberlite ore using tagged neutron method are discussed. Kimberlite ore was irradiated with fast tagged neutrons with an energy of 14.1 MeV. The elemental content of the tray with kimberlite ore was determined. The criterion for detecting diamond was the presence of excess carbon concentration in a certain region of a kimberlite sample.
DS202007-1174
2020
Rooney, T., Girard, G., Tappe, S.The impact on mantle olivine resulting from carbonated silicate melt interaction. Allikite Superior cratonContributions to Mineralogy and Petrology, Vol. 175, 15p. Canadaolivine

Abstract: Interactions between carbonated ultramafic silicate magmas and the continental lithospheric mantle results in the formation of dunite—a ubiquitous xenolith type in kimberlites and aillikites. However, whether this process dominantly occurs in the mantle source region or by subsequent interactions between lithospheric mantle fragments and transporting silica-undersaturated magmas during ascent remains debated. Aillikite magmas, which are derived from the fusion of carbonate-phlogopite metasomes under diamond-stability field upper mantle conditions, have a mineralogically more complex source than kimberlites, providing an opportunity to more fully constrain the origin of dunite xenoliths in such deeply sourced carbonated silicate magmas. Here we present a major and trace element study of olivine occurring in xenoliths and as phenocrysts in an aillikite dike located on the southern Superior Craton. We show that olivine within the dunite microxenoliths exhibits extreme enrichment in Al, Cr, Na, and V when compared to equivalent xenoliths carried by kimberlites. We interpret these results as evidence for the presence of carbonate-phlogopite metasomes left residual in the cratonic mantle source during aillikite magma formation. Our results are inconsistent with models of dunite formation through orthopyroxene dissolution upon kimberlite/aillikite magma ascent, supporting an origin for such dunites that is more closely linked to primary melt generation at the base of relatively thick continental lithosphere. Our work demonstrates that it is possible to constrain the precursor composition of cratonic mantle dunite at depth, thereby facilitating the further exploration of how carbonated silicate magmas modify and weaken continental lithospheric roots.
DS202009-1655
2020
Roseiro, J., Figueiras, J., Rodrigues, P.C.R., Mateus, A.M.Nb-bearing mineral phases in the Bailundo carbonatite complex ( Angola): implications of Nb geochemistry in metallogenesis.Communicacoes Geologicas *** in PORT, researchgate 7p. PdfAfrica, Angoladeposit - Bailundo

Abstract: Pyrochlore group minerals are common accessory phases in alkaline-carbonatitic complexes, and the most important Nb ore worldwide. Its capacity to embody a wide range of compositions can often provide useful insights in Nb occurrence and concentration processes. In the Bailundo Carbonatitic Complex (BCC, Angola), two major sets of pyrochlore can be distinguished: (1) magmatic/metasomatic pyrochlore in deep carbonatitic rocks, often displaying diffuse textures obliterating primary zoning, with slightly low contents in Nb2O5 (average 50 wt%), and in other chemical components (Ta, U, Na); and (2) supergene pyrochlore in the weathering profile, displaying corroded and bleached patches along microfractures (in some cases, with relics of magmatic pyrochlore), that show higher contents in Nb2O5 (up to 73 wt%), Ba and Pb. Compositional and textural variations recorded in pyrochlore crystals illustrate the geodynamic events that took place in the BCC and contributed to high Nb concentration in the weathering profile, thus being quite useful to distinguish different mineralization types and as Nb-exploration tools.
DS202006-0948
2020
Rossetti, F., Lucci, F., Theye, T., Bouybaouenne, M., Gerdes, A., Optiz, J., Dini, A., Lipp, C.Hercynian anatexis in the envelope of the Beni Bousera peridotites ( Alboran Domain, Morroco): implications for the tectono-metamorphic evolution of the deep crustral roots of the Mediterranean region.Gondwana Research, Vol. 83, pp. 157-162. pdfAfrica, Moroccoperidotites

Abstract: The metamorphic core of the Betic-Rif orogenic chain (Alboran Domain) is made up of lower crustal rocks forming the envelope of the Ronda (Spain) and Beni Bousera (Morocco) peridotites. The deepest sections of the crustal envelopes are made of migmatitic granulites associated with diffuse acidic magmatic products, making these exposure and ideal site to investigate the textural and petrological connection between crustal anatexis and granite magmatism in the contintental crust. However, still debated is the timing of intracrustal emplacement of the peridotite bodies, with models proposing either Alpine (early Miocene) or Hercynian ages, and still uncertain is the linkage between peridotite emplacement and crustal anatexis. In this study, by combining rock textures with whole-rock geochemistry, metamorphic thermobarometry, the U-Pb zircon geochronology and the analysis of the garnet and zircon REE chemistry, we document the P-T-t evolution of the granulite facies migmatites that form the immediate envelope of the Beni Bousera peridotites of the Rif belt. A main episode of Permo-Carboniferous (ca. 300-290?Ma) deep crustal anatexis, melt extraction and migration is documented that we link to the crustal emplacement of the Beni Bousera peridotites during collapse of the Hercynian orogen. Correlation at a regional scale suggests that the Beni-Bousera section can be tentatively correlated with the pre-Alpine (Permo-Carboniferous) basement units tectonically interleaved within the orogenic structure of the Alpine chain. The results of this study provide ultimate constraints to reconstruct the tectono-metamorphic evolution of the Alboran Domain in the Western Mediterranean and impose re-assessment of the modes and rates through which Alpine orogenic construction and collapse occurred and operated in the region.
DS202002-0216
2020
Rugenstein, J.K.C.What goes down must come up.Nature Geoscience, 3, pp. 5-7.Mantlecarbon

Abstract: Differential cycling of carbonate and organic carbon in the mantle may link the Great Oxidation Event and the subsequent increase in carbon isotope values, according to a model that links the Earth’s surface and interior.
DS202010-1873
2020
Sacco, D.Drift prospecting for kimberlite in the Slave geological Province: why your KIM-bearing sediment samples may not lead you to kimberlite.Vancouver Kimberlite Cluster, Sept. 30, 1p. AbstractCanada, Northwest territoriesgeochemistry

Abstract: Drift prospecting has been used for decades in the Slave Geological Province, NWT, to identify kimberlite indicator mineral and geochemical dispersals. These dispersals, in conjunction with geophysics and drilling, have led to many kimberlite discoveries. The sources of most well-defined dispersal patterns have been identified, and exploration must now focus on inauspicious regions where primary dispersal from kimberlite has been obscured by post-depositional changes to the landscape. Detailed surficial interpretations from readily available, high-resolution imagery and digital elevation data are a powerful asset when working in these challenging environments. Interpretations tailored to exploration provide the necessary context to unravel the complexities in the surficial geology and reconcile complex dispersal patterns. This presentation will demonstrate how the understanding and recognition of unique depositional environments and post-depositional modification of sediments can provide new insight into historical data, reduce the effort and resources required to collect new high-quality samples and inform data evaluations, ultimately providing lower-risk exploration targets.
DS202003-0359
2019
Saeseaw, S., Renfro, N.D., Palke, A.C., Sun, Z., McClure, S.F.Geographic origin of emerald.Gems & Gemology, Vol. 55, 4, pp. 614-647.South America, Colombia, China, Europe, Afghanistan, Africa, Zambiaemerald

Abstract: The gem trade has grown to rely on gemological laboratories to provide origin determination services for emeralds and other fine colored stones. In the laboratory, this is mostly accomplished by careful observations of inclusion characteristics, spectroscopic analysis, and trace element profile measurements by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS). Inclusions and spectroscopy can often separate Colombian emeralds from other sources (although there is some overlap between Colombian, Afghan, and Chinese [Davdar] emeralds). For non-Colombian emeralds, trace element analysis by LA-ICP-MS is needed in addition to information from the stone’s inclusions. The relative chemical diversity of emeralds from worldwide deposits allows confidence in origin determination in most cases. This contribution outlines the methods and criteria used at GIA for geographic origin determination for emerald.
DS202003-0360
2019
Safonov, O., Butvina, V., Limanov, E.Phlogopite forming reactions as indicators of metasomatism in the lithospheric mantle.Minerals ( MDPI), Vol. 9, 18p. PdfMantlemetasomatism

Abstract: Phlogopite is widely accepted as a major mineral indicator of the modal metasomatism in the upper mantle within a very wide P-T range. The paper reviews data on various phlogopite-forming reactions in upper-mantle peridotites. The review includes both descriptions of naturally occurring reactions and results of experiments that model some of these reactions. Relations of phlogopite with other potassic phases, such as K-richterite, sanidine and K-titanates, are discussed. These data are taken as a basis for thermodynamic modeling of the phlogopite-forming reactions for specific mantle rocks in terms of log(aH2O) ? log(aK2O) diagrams (pseudosections) using the Gibbs free energy minimization. These diagrams allow estimation of potassium-water activity relations during metasomatic transformations of mantle rocks, prediction sequences of mineral assemblages with respect to these parameters and comparison of metasomatic processes in the rocks of different composition. This approach is illustrated by examples from peridotite xenoliths from kimberlites.
DS202007-1175
2020
Sagatova, D., Shatskiy, A., Sagatov, N., Gavryushkin, P.N., Litasov, K.D.Calcium orthocarbonate, Ca2CO4-Pnma: a potential host for subducting carbon in the transition zone and lower mantle.Lithos, in press available, 22p. PdfMantlesubduction

Abstract: A novel structure of calcium orthocarbonate Ca2CO4-Pnma has been discovered using ab-initio crystal structure prediction methods (AIRSS and USPEX) based on the density functional theory. This phase appears above 13 GPa and remains stable to at least 50 GPa and 2000 K according to the calculations within quasi-harmonic approximation. Thus, the discovered phase can be stable at Earth's transition zone and lower mantle P-T conditions. The carbon atoms in the discovered phase are presented in 4-fold coordination, and its structure is similar to the high-pressure and high-temperature ?'H-Ca2SiO4 phase.
DS202008-1439
2020
Sagatova, D., Shatskiy, A., Sagatov, N., Gavryushkin, P.N., Litasov, K.D.Calcium orthocarbonate, CaCO4-Pnma: a potential host for subducting carbon in the transition zone and lower mantle.Lithos, Vol. 370-371, 105637 5p. PdfMantlesubduction

Abstract: A novel structure of calcium orthocarbonate Ca2CO4-Pnma has been discovered using ab-initio crystal structure prediction methods (AIRSS and USPEX) based on the density functional theory. This phase appears above 13 GPa and remains stable to at least 50 GPa and 2000 K according to the calculations within quasi-harmonic approximation. Thus, the discovered phase can be stable at Earth's transition zone and lower mantle P-T conditions. The carbon atoms in the discovered phase are presented in 4-fold coordination, and its structure is similar to the high-pressure and high-temperature ?'H-Ca2SiO4 phase.
DS202007-1176
2019
Saha, G., Rai, S,S., ShalivahanOccurrence of diamond in peninsular India and its relationship with deep Earth seismic properties.Journal of Earth System Science, Vol. 128, 43, 8p. PdfIndiageophysics, seismics

Abstract: An improved shear wave velocity (Vs) structure of the lithosphere of peninsular India using the surface wave tomography from the ambient noise and earthquake waveforms suggests its bipolar character. While most of the geological domains of India are characterised by a uniform lithospheric mantle of Vs?4.5 km/s, the three cratonic regions, eastern Dharwar, Bastar and Singhbhum, hosting most of the diamondiferous kimberlite fields, show significantly high Vs of 4.7 km/s and above in their lower lithosphere beyond ?90 km depth. The higher velocity could best be explained by the presence of diamond and/or eclogite along with peridotite in mantle. This unique relationship suggests the regional seismic image of lithosphere as a guide for exploration of diamonds.
DS202012-2247
2021
Saha, S., Peng, Y., Dasgupta, R., Mookherjee, M., Fischer, K.M.Assessing the presence of volatile-bearing mineral phases in the cratonic mantle as a possible cause of mid-lithospheric discontinuities.Earth and Planetary Letters, Vol.. 553, 116602, 12p. PdfMantlecratons

Abstract: A number of possible hypotheses have been proposed to explain the origin of mid-lithospheric discontinuities (MLDs), typically characterized by ?2-6% reductions in seismic shear wave velocity (VS) at depths of 60 km to ?150 km in the cratonic sub-continental lithospheric mantle (SCLM). One such hypothesis is the presence of low-shear wave velocity, hydrous and carbonate mineral phases. Although, the presence of hydrous silicates and carbonates can cause a reduction in the shear wave velocity of mantle domains, the contribution of volatile metasomatism to the origins of MLDs has remained incompletely evaluated. To assess the metasomatic origin of MLDs, we compiled experimental phase assemblages, phase proportions, and phase compositions from the literature in peridotite + H2O, peridotite + CO2, and peridotite + H2O + CO2 systems at P-T conditions where hydrous silicate and/or carbonate minerals are stable. By comparing the experimental assemblages with the compiled bulk peridotite compositions for cratons, we bracket plausible proportions and compositions of hydrous silicate and carbonate mineral phases that can be expected in cratonic SCLMs. Based on the CaO and K2O contents of cratonic peridotite xenoliths and the estimated upper limit of CO2 content in SCLM, ??10 vol.% pargasitic amphibole, ??2.1 vol.% phlogopite and ??0.2 vol.% magnesite solid solution can be stable in the SCLM. We also present new elasticity data for the pargasite end member of amphibole based on first principles simulations for more accurate estimates of aggregate VS for metasomatized domains in cratonic mantle. Using the bracketed phase compositions, phase proportions, and updated values of elastic constants for relevant mineral end members, we further calculate aggregate VS at MLD depths for three seismic stations in the northern continental U.S. Depending on the choice of background wave speeds of unmetasomatized peridotite and the cratonic geotherm, the composition and abundance of volatile-bearing mineral phases bracketed here can explain as much as 2.01 to 3.01% reduction in VS. While various craton formation scenarios allow formation of the amphibole and phlogopite abundances bracketed here, presence of volatile-bearing phases in an average cratonic SCLM composition cannot explain the entire range of velocity reductions observed at MLDs. Other possible velocity reduction mechanisms thus must be considered to explain the full estimated range of shear wave speed reduction at MLD depths globally.
DS202012-2248
2020
Sahoo, S., Sreenivasan, B.Response of Earth's magnetic field to large lower mantle heterogeneity.Earth and Planetary Letters, Vol. 550, 116507, 11p. PdfRussia, Canadageophysics - magnetics

Abstract: A simplified two-fold pattern of convection in the Earth's core is often used to explain the non-axisymmetric magnetic flux concentrations in the present day geomagnetic field. For large lateral variations in the lower mantle heat flux, however, a substantial east-west dichotomy in core convection may be expected. This study examines the effect of a large lateral variation in heat flux at the outer boundary in cylindrical annulus experiments that achieve approximate geostrophy of the convection as well as in rapidly rotating spherical shell simulations. In either geometry, the imposed boundary heat flux is derived from the seismic shear wave velocity in the lowermost mantle. The pattern of large-scale convection in the simulations closely follows that in the annulus experiments, which suggests that the lateral buoyancy at the equator essentially determines the structure of core convection. In particular, the location of a coherent downwelling that forms beneath Canada in mildly driven convection entirely switches over to the Siberian region in strongly driven states. Spherical dynamo models in turn show that this eastward migration of convection causes the relative instability or even the disappearance of the high-latitude magnetic flux in the Western hemisphere. Finally, large radial buoyancy causes homogenization of convection, which may place an upper bound for the Rayleigh number in the core.
DS202007-1177
2020
Salnikova, E.B., Samsonov, A.V., Stepanova, A.V., Veselovskiy, R.V., Egorova, S.V., Arzamastsev, A.A., Erofeeva, K.G.Fragments of Paleoproterozoic large igneous provinces in northern Fennoscandia: baddeleyite U-Pb age data for mafic dykes and sills.Doklady Earth Sciences, Vol. 491, pp. 227-230.Europe, Russia, Kola Peninsulageochronology

Abstract: New data on the age of dolerite dikes in the NE part of the Kola province of the Fennoscandinavian shield and the picrodolerite sills that cut the dikes are presented. The results of U-Pb ID-TIMS baddeleyite dating indicate that dolerites were formed between 2508 ± 6 and 2513 ± 16 Ma ago, simultaneously with the intrusions of the Monchegorsk group. A comparison of the composition of the dolerites studied with dykes of the same age found in other Archean cratons shows their significant similarity and suggests their formation at the same large magmatic province. The age of baddeleyite from the picrodolerites sills at 2403 ± 12 Ma ago indicates an event of basic magmatism that was not previously established in this part of the Fennoscandinavian shield. It is possible that, along with dolerite dykes with an age of 2405 Ma and komatiites of the Vetreny belt of the Karelian craton, sills of the Kola province are a component of a unified large magmatic event.
DS202002-0217
2019
Santos Santiago, J., da Silva Souza, V., Dantas, E.L., de Oliveira. C.G.Ediacaran emerald mineralization in northeastern Brazil: the case of the Fazenda Bonfim deposit.Brazil Journal of Geology ( www.scielo.br) ENG, 14p. PdfSouth America, Brazildeposit - Fazenda Bonfim

Abstract: The Fazenda Bonfim emerald deposit lies within the Seridó Belt. It is a classic example of deposit formed through metasomatic interactions between Be-rich granite intrusions and Cr(± V)-rich mafic-ultramafic rocks. The setting of the emerald mineralization was built under strong strike-slip dynamics, which produced serpentinization and talcification of mafic-ultramafic host-rocks, and was followed by syn-kinematic emplacement of Be-rich albite granite, favoring hydrothermal/metasomatic processes. The structural control and lithological-contrast were fundamental to the fluid flow and the best ore-shoot geometry, developed in the S-foliation intra-plane at the contact zone (phlogopite hornfels) between mafic-ultramafic rocks and the albite granite. Subsequently, an albitization process, linked to the final-stage of magmatic crystallization, led to an overall mineralogical and chemical change of the albite granite. 207U-235Pb data revealed inheritance ages from Archean to Neoproterozoic and a crystallization age of 561 ± 4 Ma for albite granite. However, 40Ar/39Ar data revealed plateau age of 553 ± 4 Ma for phlogopite hornfels, interpreted as the closure time for the metasomatic event responsible for the nucleation and growth of emerald crystals. The short interval of time between U-Pb and Ar-Ar data indicates an intense, but not protracted, metasomatic history, probably due to low volume of intrusive magma.
DS202001-0037
2020
Santosh, M., Tsunogae, T., Yang, C-X., Han, T-S., Hari, K.R., Prasanth, M.P.M., Uthup, S.The Bastar craton, central India: a window to Archean - Paleoproterozic crustal evolution.Gondwana Research, Vol. 79, pp. 157-184.Indiacraton

Abstract: The Bastar craton in central India, surrounded by cratonic blocks and Paleoproterozoic to Neoproterozoic orogenic belts, is a window to investigate the Archean-Paleoproterozoic crustal evolution and tectonic processes. Here we propose a new tectonic classification of the craton into the Western Bastar Craton (WBC), Eastern Bastar Craton (EBC), and the intervening Central Bastar Orogen (CBO). We present petrologic, geochemical and zircon U-Pb, REE and Lu-Hf data from a suite of rocks from the CBO and along the eastern margin of the WBC Including: (1) volcanic successions comprising meta-andesite and fine-grained amphibolite, representing arc-related volcanics along a convergent margin; (2) ferruginous sandstone, in association with rhyolite, representing a volcano-sedimentary succession, deposited in an active trench; and (3) metamorphosed mafic-ultramafic suite including gabbro, pyroxenite and dunite invaded by trondhjemite representing the section of sub-arc mantle and arc root adjacent to a long-lasting subduction system. Petrologic studies indicate that the mafic-ultramafic suite crystallized from an island arc tholeiitic parental magma in a suprasubduction zone environment. The chondrite-normalized and primitive mantle normalized diagrams of the mafic and ultramafic rocks suggest derivation from MORB magma. The mixed characters from N-MORB to E-MORB of the studied samples are consistent with subduction modification of a MORB related magma, involving partial melting of the metasomatized mantle wedge. Our zircon U-Pb age data suggest that the cratonic nuclei was constructed as early as Paleoarchean. We present evidence for active subduction and arc magmatism through Mesoarchean to Neoarchean and early Paleoproterozoic, with the trench remaining open until at least 2.3?Ga. Two major crust building events are recognized in the Bastar craton: during Mesoarchean (recycled Paleoarchean subduction-related as well as juvenile/depleted mantle components) and Neoarchean (accretion of juvenile oceanic crust, arc magmatism including granite batholiths and related porphyry mineralization). The final cratonization occurred during latest Paleoproterozoic, followed by collisional assembly of the craton and its incorporation within the Peninsular Indian mosaic during Mesoproterozoic. In the global supercontinent context, the craton preserves the history of Ur, the earliest supercontinent, followed by the Paleo-Mesoproterozoic Columbia, as well as minor thermal imprints of the Neoproterozoic Rodinia and associated Grenvillian orogeny.
DS202003-0361
2020
Santosh, M., Tsunogae, T., Yang, C-X., Han, Y-S., Hari, K.R., Manu Prasanth, M.P., Uthup, S.The Bastar craton, central India: a window to Archean - Paleoproterozoic crustal evolution.Gondwana Research, Vol. 79, pp. 157-184.Indiacraton

Abstract: The Bastar craton in central India, surrounded by cratonic blocks and Paleoproterozoic to Neoproterozoic orogenic belts, is a window to investigate the Archean-Paleoproterozoic crustal evolution and tectonic processes. Here we propose a new tectonic classification of the craton into the Western Bastar Craton (WBC), Eastern Bastar Craton (EBC), and the intervening Central Bastar Orogen (CBO). We present petrologic, geochemical and zircon U-Pb, REE and Lu-Hf data from a suite of rocks from the CBO and along the eastern margin of the WBC Including: (1) volcanic successions comprising meta-andesite and fine-grained amphibolite, representing arc-related volcanics along a convergent margin; (2) ferruginous sandstone, in association with rhyolite, representing a volcano-sedimentary succession, deposited in an active trench; and (3) metamorphosed mafic-ultramafic suite including gabbro, pyroxenite and dunite invaded by trondhjemite representing the section of sub-arc mantle and arc root adjacent to a long-lasting subduction system. Petrologic studies indicate that the mafic-ultramafic suite crystallized from an island arc tholeiitic parental magma in a suprasubduction zone environment. The chondrite-normalized and primitive mantle normalized diagrams of the mafic and ultramafic rocks suggest derivation from MORB magma. The mixed characters from N-MORB to E-MORB of the studied samples are consistent with subduction modification of a MORB related magma, involving partial melting of the metasomatized mantle wedge. Our zircon U-Pb age data suggest that the cratonic nuclei was constructed as early as Paleoarchean. We present evidence for active subduction and arc magmatism through Mesoarchean to Neoarchean and early Paleoproterozoic, with the trench remaining open until at least 2.3?Ga. Two major crust building events are recognized in the Bastar craton: during Mesoarchean (recycled Paleoarchean subduction-related as well as juvenile/depleted mantle components) and Neoarchean (accretion of juvenile oceanic crust, arc magmatism including granite batholiths and related porphyry mineralization). The final cratonization occurred during latest Paleoproterozoic, followed by collisional assembly of the craton and its incorporation within the Peninsular Indian mosaic during Mesoproterozoic. In the global supercontinent context, the craton preserves the history of Ur, the earliest supercontinent, followed by the Paleo-Mesoproterozoic Columbia, as well as minor thermal imprints of the Neoproterozoic Rodinia and associated Grenvillian orogeny.
DS202001-0038
2019
Saplakoglu, Y.Extraterrestrial mineral never before seen on Earth found inside a famous meteorite. Wedderburn ( found 1951 near Victoria)LiveScience.com, Sept. 4, 1p.Australiameteorite
DS202009-1656
2020
Sasse, D., Jones, T.J., Russell, J.K.Transport, survival and modification of xenoliths and xenocrysts from source to surface.Earth and Planetary Science Letters, Vol. 548, 12p. PdfMantlekimberlite ascent

Abstract: A wide variety of magmas entrain, transport and erupt mantle material in the form of xenoliths and xenocrysts. The host magmas are often low viscosity in nature and range from basalt to more esoteric compositions such as kimberlite, nephelinite and basanite. Here we focus on kimberlite magmas which are particularly successful at transporting deep mantle cargo to the surface, including economically important quantities of diamond. Collections of mantle-derived xenoliths and xenocrysts are critical to our understanding of the structure, stability, composition, thermal state, age, and origin of the lithosphere. However, they also inform on magma transport conditions. Through a series of scaled analogue experiments, we document the relative mechanical stability of olivine, garnet, orthopyroxene, clinopyroxene and diamond xenocrysts during magma ascent. Our experiments fluidized these mantle minerals at a constant gas flux for variable amounts of time approximating transport in a high velocity, turbulent, fluid-rich (supercritical fluid or gas, depending on depth) magma. The evolution of mineral surface features, morphology and grain size distributions is analyzed as a function of residence time. We show that on timescales consistent with magma ascent, each mantle mineral is subject to mechanical modification resulting in mass loss and reshaping (rounding) by grain size reduction and surface pitting. We further discuss the chemical consequences of producing fine particle chips that are highly susceptible to dissolution. Lastly, we utilize an empirical model that relates textural observations (e.g. impact pit size) on xenocrysts to differential particle velocities. Our approach applied to natural kimberlitic olivine and garnet xenocrysts indicates differential velocities of - the first direct estimate for velocity in an ascending kimberlite magma.
DS202012-2249
2020
Schmetzer, K., Martayan, G., Blake, A.R.History of the Chivor emerald mine, part 2 ( 1924-1970): between insolvency and viability.Gems & Gemology, Vol. 56, 2, summer pp. 230-257. pdfSouth America, Columbiadeposit - Chivor

Abstract: The history of the Chivor emerald mine in Colombia is a saga with countless twists and turns, involving parties from across the globe. Indigenous people initially exploited the property, followed by the Spanish in the sixteenth and seventeenth centuries, before abandonment set in for 200 years. The mine was rediscovered by Francisco Restrepo in the 1880s, and ownership over the ensuing decades passed through several Colombian owners and eventually to an American company, the Colombian Emerald Syndicate, Ltd., with an intervening but unsuccessful attempt by a German group organized by Fritz Klein to take control. With the Colombian Emerald Syndicate succumbing to bankruptcy in 1923, the property was sold and then transferred in 1924 to another American firm, the Colombia Emerald Development Corporation. Under the new ownership, stock market speculation played a far more prominent role in the story than actual mining. Nonetheless, periods of more productive mining operations did take place under managers Peter W. Rainier and Russell W. Anderton. Yet these were not enough to prevent the company, renamed Chivor Emerald Mines, Inc. in 1933, from entering insolvency in 1952 and being placed into receivership. Leadership by Willis Frederick Bronkie enabled the firm to regain independence in 1970 and shortly thereafter to be sold in a series of transactions, with Chivor gradually being returned to Colombian interests.
DS202005-0759
2020
Seales, J., Lenardic, A.Deep water cycling and multi-stage cooling of the Earth.Researchgate preprint, 32p. PdfMantlegeothermometry

Abstract: Paleo-temperature data indicates that the Earth's mantle did not cool at a constant rate over geologic time. Post magma ocean cooling was slow with an onset of more rapid mantle cooling between 2.5 and 3.0 Gyr. We explore the hypothesis that this multi-stage cooling is a result of deep water cycling coupled to thermal mantle convection. As warm mantle ascends, producing melt, the mantle is dehydrated. This tends to stiffens the mantle, which slows convective vigor causing mantle heating. At the same time, an increase in temperature tends to lower mantle viscosity which acts to increase convective vigor. If these two tendencies are in balance, then mantle cooling can be weak. If the balance is broken, by a switch to a net rehydration of the mantle, then the mantle can cool more rapidly. We use coupled water cycling and mantle convection models to test the viability of this hypothesis. We test models with different parameterizations to allow for variable degrees of plate margin strength. We also perform a layered uncertainty analysis on all the models to account for input, parameter, and structural model uncertainties. Within model and data uncertainty, the hypothesis that deep water cycling, together with a combination of plate strength and mantle viscosity resisting mantle overturn, can account for paleo data constraints on mantle cooling.
DS202008-1440
2020
Seales, J., Lenardic, A.Deep water cycling and the multi-stage cooling of the Earth.Preprint, doi:101340/RG2.2.25986.63683 32p. PdfMantlethermal convection

Abstract: Paleo-temperature data indicates that the Earth's mantle did not cool at a constant rate over geologic time. Post magma ocean cooling was slow with an onset of more rapid mantle cooling between 2.5 and 3.0 Gyr. We explore the hypothesis that this multi-stage cooling is a result of deep water cycling coupled to thermal mantle convection. As warm mantle ascends, producing melt, the mantle is dehydrated. This tends to stiffens the mantle, which slows convective vigor causing mantle heating. At the same time, an increase in temperature tends to lower mantle viscosity which acts to increase convective vigor. If these two tendencies are in balance, then mantle cooling can be weak. If the balance is broken, by a switch to a net rehydration of the mantle, then the mantle can cool more rapidly. We use coupled water cycling and mantle convection models to test the viability of this hypothesis. We test models with different parameterizations to allow for variable degrees of plate margin strength. We also perform a layered uncertainty analysis on all the models to account for input, parameter, and structural model uncertainties. Within model and data uncertainty, the hypothesis that deep water cycling, together with a combination of plate strength and mantle viscosity resisting mantle overturn, can account for paleo data constraints on mantle cooling.
DS202008-1441
2020
Semple, A., Lenardic, A.On the robustness of asthenosphere plug flow in mantle convection models with plate like behaviour.Researchgate, 11p. PdfMantleconvection

Abstract: Conventional wisdom holds that the motion of tectonic plates drives motion in the Earth’s rocky interior (i.e., in the Earth’s asthenosphere). Recent seismological observations have brought this view into question as they indicate that the velocity of the asthenosphere can exceed tectonic plate velocity. This suggests that interior motions can drive plate motions. We explore models of coupled plate tectonics and interior motions to address this discrepancy. The models reveal that the coupling between plates and the asthenosphere is not an issue of plates drive asthenosphere motion or asthenosphere motion drives plates. Both factors work in tandem with the balance being a function of plate margins strength and asthenosphere rheology. In particular, a power-law viscosity allows pressure gradients to generate interior flow that can locally drive plate motion. The models also reveal a hysteresis effect that allows different tectonic states (plate tectonics versus a single plate planet) to exist at the same parameter conditions. This indicates that history and initial conditions can play a role in determining if a planet will or will not have plate tectonics.
DS202010-1874
2020
Semple, A., Lenardic, A.The robustness of pressure-driven asthenospheric flow in mantle convection models with plate-like behavior.Geophysical Research Letters, 10.1029/2020/GL089556 11p. PdfMantleconvection

Abstract: It is generally thought that tectonic plates drive motion in the Earth's rocky interior. Recent observations have challenged this view as they indicate that interior motion can drive tectonic plates. Models of coupled tectonics and interior flow are used to address this discrepancy. The models reveal that the question of “does plate tectonics drive interior flow or does interior flow drive plate tectonics” may be ill founded as both possibilities may be active at the same time. The balance between the two drivers is found to depend on plate margin strength. The models also reveal that different tectonic modes can exist under the same physical conditions. This indicates a planet's initial state can determine if it will or will not have plate tectonics.
DS202010-1875
2020
Service, R.F.The carbon vault. ( refers to Gahcho Kue crushed rock waste )as a vault to lock up CO2.Science, Vol. 369, 6508, pp. 1156-1159. pdfCanada, Northwest territoriesrock waste
DS202003-0362
2020
Sha, X., Yue, W., Zhang, H., Qin, W., She, D., Wang, C.Thermal stability of polycrystalline diamond compact sintered with boron coated diamond particles.Diamond & Related Materials, in press available, 34p. PdfGlobalboron

Abstract: The polycrystalline diamond compact (PDC), which consists of a polycrystalline diamond layer on a tungsten carbide (WC)/cobalt (Co) substrate, is extensively utilized as drilling bits. However, the poor thermal stability due to the graphitization and oxygen susceptibility of diamond severely limits the application of PDCs to high-temperature drilling work. In this study, a new PDC with improved thermal stability is successfully synthesized with boron (B)-coated diamond particles, which forms a uniform boron carbide (B4C) barrier. The as-received B4C phase acts as a protective barrier, which enhances the initial graphitization and oxidizing temperatures to 800 °C and 780 °C, respectively, which are ~100 °C and ~30 °C higher than those (700 °C and 750 °C) of the PDC sintered with uncoated diamond particles. The B4C barrier protects diamond grains from direct contact with the Co phase, prohibiting the cobalt-catalytic graphitization. In addition, the oxidation of the B4C barrier occurs prior to that of the diamond grains, which inhibits the PDC from oxidation.
DS202009-1657
2020
Shaikh, A.M., Tappe, S., Bussweiler, Y., Patel, S.C., Ravi, S., Bolhar, R., Viljoen, F.Clinopyroxene and garnet mantle cargo in kimberlites as probes of Dharwar craton architecture and geotherms, with implications for post-1.1 Ga lithosphere thinning events beneath southern India.Journal of Petrology, in press available, 73p. PdfIndiadeposit - Wajrakarur

Abstract: The Wajrakarur Kimberlite Field (WKF) on the Eastern Dharwar Craton in southern India hosts several occurrences of Mesoproterozoic kimberlites, lamproites, and ultramafic lamprophyres, for which mantle-derived xenoliths are rare and only poorly preserved. The general paucity of mantle cargo has hampered the investigation of the nature and evolution of the continental lithospheric mantle (CLM) beneath cratonic southern India. We present a comprehensive study of the major and trace element compositions of clinopyroxene and garnet xenocrysts recovered from heavy mineral concentrates for three ca. 1.1 Ga old WKF kimberlite pipes (P7, P9, P10), with the goal to improve our understanding of the cratonic mantle architecture and its evolution beneath southern India. The pressure-temperature conditions recorded by peridotitic clinopyroxene xenocrysts, estimated using single-pyroxene thermobarometry, suggest a relatively moderate cratonic mantle geotherm of 40?mW/m2 at 1.1 Ga. Reconstruction of the vertical distribution of clinopyroxene and garnet xenocrysts, combined with some rare mantle xenoliths data, reveals a compositionally layered CLM structure. Two main lithological horizons are identified and denoted as layer A (?80-145?km depth) and layer B (?160-190?km depth). Layer A is dominated by depleted lherzolite with subordinate amounts of pyroxenite, whereas layer B comprises mainly refertilised and Ti-metasomatised peridotite. Harzburgite occurs as a minor lithology in both layers. Eclogite stringers occur within the lower portion of layer A and at the bottom of layer B near the lithosphere-asthenosphere boundary at 1.1 Ga. Refertilisation of layer B is marked by garnet compositions with enrichment in Ca, Ti, Fe, Zr and LREE, although Y is depleted compared to garnet in layer A. Garnet trace element systematics such as Zr/Hf and Ti/Eu indicate that both kimberlitic and carbonatitic melts have interacted with and compositionally overprinted layer B. Progressive changes in the REE systematics of garnet grains with depth record an upward percolation of a continuously evolving metasomatic agent. The intervening zone between layers A and B at ?145-160?km depth is characterised by a general paucity of garnet. This ‘garnet-paucity’ zone and an overlying type II clinopyroxene-bearing zone (?115-145?km) appear to be rich in hydrous mineral assemblages of the MARID- or PIC kind. The composite horizon between ?115-160?km depth may represent the product of intensive melt/rock interaction by which former garnet was largely reacted out and new metasomatic phases such as type II clinopyroxene and phlogopite plus amphibole were introduced. By analogy with better-studied cratons, this ‘metasomatic horizon’ may be a petrological manifestation of a former mid-lithospheric discontinuity at 1.1 Ga. Importantly, the depth interval of the present-day lithosphere-asthenosphere boundary beneath Peninsular India as detected in seismic surveys coincides with this heavily overprinted metasomatic horizon, which suggests that post-1.1 Ga delamination of cratonic mantle lithosphere progressed all the way to mid-lithospheric depth. This finding implies that strongly overprinted metasomatic layers, such as the ‘garnet-paucity’ zone beneath the Dharwar craton, present structural zones of weakness that aid lithosphere detachment and foundering in response to plate tectonic stresses.
DS202009-1658
2020
Shang, S.Y., Tong, Y., Zhang, S.X., Huang, F.L.Study on phase transformation mechanism of various carbon sources in detonation synthesis of diamond.Fullerenes, nanotubes and carbon nanostructures, Vol. 28, 11, pp. 877-885.globalsynthetics

Abstract: In this paper, the phase transformation mechanism of various carbon sources in the synthesis of diamond by direct detonation method was studied. Through designing comparison experiment and the X-ray diffraction (XRD) characterization technique, an experimental study was conducted on the detonation process with the external of the combined carbon source and free carbon source, and without the participation of the external carbon source. The laws of phase transformation of the various carbon sources are obtained, in which the surplus carbon in the explosives participates in the formation of diamonds through the collision growth of droplet-like carbon, the added bonded carbon does not participate in the synthesis of diamond, and the added free carbon forms diamonds through the Martensitic transformation.
DS202011-2060
2020
Shardell, J.Triplet conductivity in diamonds.Materials World Magazine, https://www.iom3.org/materials-world-magazine/news/2020/oct/13/triplet-conductivity-diamondsAfrica, South Africananodiamonds
DS202008-1442
2018
Sharma, A., Kumar, A., Pankaj, P., Pandit, D., Chakrabarti, R., Chalapathi Rao, N.V.Petrology and Sr-Nd isotpe systematics of the Ahobil kimberlite pipe ( Pipe -16) from the Wajrakarur field, eastern Dharwar craton, southern India.Geoscience Frontiers, 20p. PdfIndiadeposit - Ahobil Pipe 16
DS202004-0532
2020
Sharygin, V.V., Britvin, S.N., Kaminsky, F.V., Wirth, R., Nigmatulina, E.N., Yakovlev, G.A., Novoselov, K.A., Murashko, M.N.Ellinaite IMA No. 2019-091 mineral name( gravel of Sorriso creek, Aripuna River).European Journal of Mineralogy, Vol. 32, p. 211.Europe, Israel, South America, Brazil, Mato Grossodiamond inclusion
DS202009-1659
2020
Shatskiy, A., Arefiev, A.V.,Podborodnikov, I.V., Litasov, K.D.Liquid immiscibility and phase relations in the system KAlSi0308-CaMg ( CO3)2+- NaAiSi2O6+- Na2CO3 at Gpa: implications for diamond forming melts.Chemical Geology, Vol. 550, 17p. PdfMantlemelting

Abstract: To evaluate the effect of Na on the carbonate-silicate liquid immiscibility in the diamond stability field, we performed experiments along some specific joins of the system KAlSi3O8-CaMg(CO3)2 ± NaAlSi2O6 ± Na2CO3 at 6 GPa. Melting in all studied joins begins at 1000-1050 °C. The melting in the Kfs + Dol system is controlled by the reaction 6 KAlSi3O8 (K-feldspar) + 6 CaMg(CO3)2 (dolomite) = 2 (Can,Mg1-n)3Al2Si3O12 (garnet) + Al2SiO5 (kyanite) + 11 SiO2 (coesite) + 3 K2(Ca1-n,Mgn)2(CO3)3 (carbonatitic melt) + 3 CO2 (fluid), where n ~ 0.3-0.4. A temperature increasing to 1300 °C yields an appearance of the silicic immiscible melt in addition to carbonatitic melt via the reaction K2CO3 (carbonatitic melt) + Al2SiO5 (kyanite) + 5 SiO2 (coesite) = 2 KAlSi3O8 (silicic melt) + CO2 (fluid or solute in melts). The silicic melt composition is close to KAlSi3O8 with dissolved CaMg(CO3)2 and molecular CO2. An addition of NaAlSi2O6 or Na2CO3 to the system results in partial decomposition of K-feldspar and formation of K-bearing carbonates, (K, Na)2Mg(CO3)2 and (K, Na)2Ca3(CO3)4. Their melting produces carbonatite melt with the approximate composition of 4(K, Na)2CO3•6Ca0.6Mg0.4CO3 and magnesite. Besides, the presence of NaAlSi2O6 in the studied system shifts the lower-temperature limit of immiscibility to 1500°?, while the presence of Na2CO3 eliminates the appearance of silicic melt by the following reaction: 2 KAlSi3O8 (in the silicic melt) + Na2CO3 = 2 NaAlSi2O6 (in clinopyroxene) + K2CO3 (in the carbonatitic melt) + SiO2 (coesite). Thus, an increase of the Na2O content in the system Na2O-K2O-CaO-MgO-Al2O3-SiO2-CO2 consumes Al2O3 and SiO2 from silicic melt to form clinopyroxene. We found that grossular-pyrope and diopside-jadeite solid solutions can coexist with CO2 fluid at 900-1500 °C and 6 GPa. Thus, CO2 fluid is stable in the eclogitic suite in the diamond stability field under temperature conditions of the continental lithosphere and subducting slabs. Variations in the Na2O content observed in carbonatitic melts trapped by natural in diamonds exceed those derived by the pelite melting. The present experiments show that an addition of NaAlSi2O6 to the Kfs + Dol system does not cause an increase of the Na2O content in the carbonatitic melt, whereas the addition of Na2CO3 at Na2O/Al2O3 > 1 yields the formation of the melts with the Na2O contents covering the entire range of natural compositions. Thus, only the presence of additional salt components can explain the elevated Na2O content in the melts trapped in lithospheric diamonds. In addition to carbonates, sodium can be hosted by chlorides, sulfates, etc.
DS202009-1660
2020
Shatskiy, A., Bekhtenova, A., Podborodnikov, I.V., Arefiev, A.V., Litasov, K.D.Metasomatic interaction of the eutectic Na- and K-bearing carbonate melts with natural garnet lherzolite at 6 Gpa and 1100-1200 C: toward carbonatite melt composition in SCLM.Lithos, Vol. 374-375, 17p. PdfMantlemetasomatism

Abstract: The range of carbonatite melts in equilibrium with the subcontinental lithospheric mantle (SCLM) under geothermal conditions is limited by alkali-rich near-eutectic compositions. Therefore, here we employed eutectic Na/K-Ca-Mg-Fe carbonate mixtures to model the interaction of a metasomatic carbonatite melt with natural garnet lherzolite. The experiments were performed at 1100 and 1200 °C and 6 GPa in graphite capsules using a multianvil press. The run duration was 111 and 86 h, respectively. To verify achieving an equilibrium, a synthetic mixture identical to natural lherzolite was also employed. We have found that both Na- and K-bearing carbonatite melts cause wehrlitization accompanying by the elimination of orthopyroxene and an increase of CaO in garnet at a constant Cr2O3. Interaction with the K?carbonatite melt alters clinopyroxene composition toward lower Na2O (0.2-0.3 wt%), and higher K2O (0.5-1.0 wt%), whereas the Na?carbonatite melt revealed the opposite effect. The resulting melts have a following approximate composition [40(Na, K)2CO3?60Ca0.5Mg0.4Fe0.1CO2 + 0.6-1.4 wt% SiO2] displaying a decrease in Ca# at a nearly constant alkali content relative to the initial composition, where Ca# = 100?Ca/(Ca + Mg + Fe). We have also found that alkali-poor (? 20 mol% (Na, K)2CO3) carbonate mixtures do not melt completely but yield magnesite and alkali- and Ca-rich melts like those in the systems with eutectic mixtures. Under SCLM P-T conditions the range of carbonatite melt compositions is restricted by the full melting field of alkali-rich carbonates in the corresponding Na/K-Ca-Mg carbonate systems. Infiltration of less alkaline higher-temperature carbonatite melt in SCLM and its subsequent cooling to the ambient mantle temperature, 1100-1200 °C at 6 GPa, should cause crystallization of magnesite and shift the melt composition to [30(Na, K)2CO3?70Ca0.6Mg0.3Fe0.1CO3]. Owing to its high Ca#, this melt is not stable in equilibrium with orthopyroxene yielding its disappearance by CaMg exchange reaction producing clinopyroxene, magnesite, and shifting the melt composition toward higher alkali content. The melts containing 40-45 mol% of alkaline carbonates have no limitation in Ca# because the corresponding binary NaMg and KMg carbonate eutectics are located near 1200 °C. Therefore, these melts can achieve Ca# ? 30-40 and, be in equilibrium with garnet lherzolites and harzburgites under the geothermal condition of SCLM. Considering the present results and previous experimental data the following ranges of carbonatite melt compositions can be expected in equilibrium with garnet peridotites at the base of SCLM: Ca# < 30 and > 30 mol% (K, Na)2CO3 in equilibrium with harzburgite; Ca# 30-40, >25 mol% (K, Na)2CO3 in equilibrium with lherzolite; and Ca# 40-60 and >20 mol% (K, Na)2CO3 in equilibrium with wehrlite.
DS202012-2250
2020
Shatskiy, A., Bekhtenova, A., Podbororodnikov, I.V., Arefiev, A.V.Carbonate melt interaction with natural eclogite at 6 Gpa and 1100-1200 C Implcations for metasomatic melt composition in subcontinental lithospheric mantle.Chemical Geology, Vol. 558, 119915, 15p. PdfMantlecarbonatite

Abstract: Compositional ranges of carbonate melts stable under P-T conditions corresponding to the base of subcontinental lithospheric mantle (SCLM) are limited by alkali-rich near-eutectic compositions. In the present work, we investigated the interaction of such melts with the natural eclogite of Group A. It was found that the interaction is accompanied by decreasing Ca# in the melt (L) and increasing Ca# in garnet (Grt) according to the reaction: 3CaCO3 (L) + Mg3Al2Si3O12 (Grt) = 3MgCO3 (Mgs and/or L) + Ca3Al2Si3O12 (Grt), where Mgs is magnesite. The interaction with the Na-Ca-Mg-Fe carbonate melt increases amount of jadeite component in clinopyroxene (Cpx) consuming Al2O3 from garnet and Na2O from the melt according to the reaction: Na2CO3 (L) + CaCO3 (L) + 2Mg3Al2Si3O12 (Grt) + 2CaMgSi2O6 (Cpx) = 2NaAlSi2O6 (Cpx) + Ca3Al2Si3O12 (Grt) + 2MgCO3 (Mgs, L) + 3Mg2SiO4 (Ol). As a result, garnet and omphacite compositions evolve from eclogite Group A to eclogite Group B. A byproduct of the reaction is olivine (Ol), which may explain the formation of inclusions of “mixed” eclogite (garnet + omphacite) and peridotite (olivine) paragenesis in lithospheric diamonds. The interaction with the K-Ca-Mg-Fe carbonate melt increases the K2O content in clinopyroxene to 0.5-1.2 wt%, while the Na2O content lowers to 0.3 wt%. The following range of carbonatite melt compositions can be in equilibrium with eclogite at the base of SCLM (1100-1200 °C and 6 GPa): 18(Na0.97K0.03)2CO3?82(Ca0.63Mg0.30Fe0.07)CO2-42(Na0.97K0.03)2CO3?58(Ca0.46Mg0.45Fe0.09)CO2. Our results also suggest that the partial melting of ‘dry’ carbonated eclogite, if any, at 1100 °C and 6 GPa yields the formation of a carbonate melt with the following composition (mol%) 25(Na0.96K0.04)2CO3?75(Ca0.64Mg0.31Fe0.05)CO2, corresponding to 18-27 wt% Na2O in the melt on a volatile-free basis.
DS202010-1876
2020
Shatsky, V.S., Ragozin, A.L., Kozmenko, O.A., Denisenko, A.A.Geochemical evidence for participation of the subducted crust in the process of transformation of the subcontinental mantle in the Yakutian diamondiferous province.Doklady Earth Sciences, Vol. 493, 1, pp. 513-516. pdfRussia, Yakutiasubduction

Abstract: The data available indicate the complex evolution of deformed peridotites of mantle xenoliths, the P-T parameters of which indicate that they are fragments of the metasomatized lower part of the cratonic lithosphere. The zoning established in garnets from xenoliths in kimberlite pipes is interpreted as a result of metasomatism that occurred shortly before xenoliths reached the surface. Metasomatic alterations in xenoliths of deformed harzburgites were manifested not only in the development of zoning of minerals. The study results show that there is a discrepancy between the data calculated based on the contents of incompatible elements in minerals of xenoliths and those obtained due to direct measurements of the bulk composition of xenoliths. To determine the balance of incompatible elements, we have carried out experiments on leaching xenoliths of deformed lherzolites from the Udachnaya kimberlite pipe. It was established that a significant part of LREEs in the studied xenoliths occurs in the intergranular space. The distribution pattern of incompatible elements and, in particular, the presence of a positive Eu anomaly indicate that the appearance of the intergranular component is not associated with contamination of xenoliths by the kimberlite melt. Quite a few xenoliths demonstrate a positive Eu anomaly, which indicates the influence of the subducted crustal component at one of the modification stages of xenoliths.
DS202005-0760
2020
Shatsky, V.S., Ragozin, A.L., Logvinova, A.M., Wirth, R.Diamond-rich placer deposits from iron-saturated mantle beneath the northeastern margin of the Siberian craton.Lithos, Vol. 364-365, 12p. PdfRussiadeposit - Olenek

Abstract: We demonstrate for the first time the presence of iron carbides in placer diamonds from the northeastern region of the Siberian craton. It was found that the inclusions are polycrystalline aggregates, and iron carbides filling the fissures in the diamonds, thus providing clear evidence that the iron melts were captured first. Iron carbides were identified in diamonds containing mineral inclusions of eclogitic (Kfs, sulfide) and peridotitc (olivine) paragenesis. Iron carbides with minor amounts of admixed nickel were detected in a diamond sample containing an olivine inclusion (0.3 wt% Ni), indicating that the iron melt was not in equilibrium with the mantle peridotite.The low nickel contents of the iron carbides provide the best evidence that the subducted crust is a likely source of the iron melt. Diamonds containing carbide inclusions are characterised by a relatively low nitrogen aggregation state (5-35%), which is not consistent with the high temperature of the transition zone. Therefore, we have reason to assume that the studied diamonds are from the lower regions of the lithosphere. Considering all factors, the model for the interaction of the ascending asthenospheric mantle with the subducting slab seems to be more realistic.
DS202008-1443
2020
Shirey, S.B., Smit, K.V.Age and depth of oceanic slab-derived diamonds and the formation of Archean subcontinental mantle.Goldschmidt 2020, 1p. AbstractMantleeclogite

Abstract: The Precambrian is marked by the stabilization of subcontinental mantle lithosphere and associated crystallization of lithospheric diamonds from slab-derived carbon [1,2]. These features and higher nitrogen contents are consistent with diamond fluid delivery from the crustal (eclogitic) part of the slab and keel growth by lateral accretion/advective thickening [e.g. 3-5] in shallow and reducing mantle wedge settings. Such diamonds are rare to non-existent in the Phanerozoic. Sublithospheric diamonds are also slab-derived but from nitrogen-poor fluids/melts. These diamond fluids were delivered from deeper carbonated crustal or serpentinized mantle portions of cold slabs that subducted into the mantle transition zone regions and warmed up. While the age of such sublithospheric diamonds is poorly known, current mantle tomogrpahy shows that these conditions are a feature of the modern Earth and are consistent with the few ages that show these diamonds are younger. Aside from depth differences, the conditions for the crystallization of slab-associated lithospheric vs sublithospheric diamonds are fundamentally different in slab temperature, fluid composition, and fluid source within the slab source-rock. We hypothesize that these differences between lithospheric and sublithospheric diamonds may also be of temporal significance. If so, slab-derived diamond petrogenesis could be a key to understanding why cratonic keel formation is prevalent in the early Precambrian. Slabderived diamonds provide evidence for a transition from Precambrian conditions of shallow-devolatilization and warmer, more buoyant plates, that would facilitate lithosphere thickening to Phanerozoic conditions of deeperdevolatilization, cooler, and less buoyant plates, that are less conducive to lithosphere thickening.
DS202001-0039
2020
Shirey, S.B., Smit, K.V., Pearson, D.G., Walter, M.J., Aulbach, S., Brenker, F.E., Bureau, H., Burnham, A.D., Cartigny, P., Chacko, T., Frost, D.J., Hauri, E.H., Jacob, D.E., Jacobsen, S.D., Kohn, S.C., Luth, R.W., Mikhail, S., Navon, O., Nestola, F., NimDiamonds and mantle geodynamics of carbon: IN: Deep Carbon: past to present. Editors Orcutt, Danielle, Dasgupta, pp. 89-128.Mantlegeodynamics

Abstract: The science of studying diamond inclusions for understanding Earth history has developed significantly over the past decades, with new instrumentation and techniques applied to diamond sample archives revealing the stories contained within diamond inclusions. This chapter reviews what diamonds can tell us about the deep carbon cycle over the course of Earth’s history. It reviews how the geochemistry of diamonds and their inclusions inform us about the deep carbon cycle, the origin of the diamonds in Earth’s mantle, and the evolution of diamonds through time.
DS202010-1877
2018
Simandl, G.J., Paradis, S.Carbonatites: related ore deposits, resources, footprint, and exploration methods.Applied Earth Science Transactions of the Institute of Mining and Metallurgy, doi.org/10.1080/ 25726838.2018.1516935 32p. Pdf Globalcarbonatite

Abstract: Most carbonatites were emplaced in continental extensional settings and range in age from Archean to recent. They commonly coexist with alkaline silicate igneous rocks, forming alkaline-carbonatite complexes, but some occur as isolated pipes, sills, dikes, plugs, lava flows, and pyroclastic blankets. Incorporating cone sheets, ring dikes, radial dikes, and fenitisation-type halos into an exploration model and recognising associated alkaline silicate igneous rocks increases the footprint of the target. Undeformed complexes have circular, ring, or crescent-shaped aeromagnetic and radiometric signatures. Carbonatites can be effectively detected by soil, till, and stream-sediment geochemical surveys, as well as biogeochemical and indicator mineral surveys Carbonatites and alkaline-carbonatite complexes are the main sources of rare earth elements (REE) and Nb, and host significant deposits of apatite, vermiculite, Cu, Ti, fluorite, Th, U, natural zirconia, and Fe. Nine per cent of carbonatites and alkaline-carbonatite complexes contain active or historic mines, making them outstanding multi-commodity exploration targets.
DS202005-0761
2019
Singh, T.D., Manikyamba, C., Subramanyam, K.S.V., Ganguly, S., Khelen, A., Ramakrsihna Reddy, N.Mantle heterogeneity, plume-lithosphere interaction at rift controlled ocean-continent transition zone: evidence from trace PGE geochemistry of Vempalle flows, Cuddapah basin India.Geoscience Frontiers, in press, 20p. PdfIndiaREE

Abstract: This study reports major, trace, rare earth and platinum group element compositions of lava flows from the Vempalle Formation of Cuddapah Basin through an integrated petrological and geochemical approach to address mantle conditions, magma generation processes and tectonic regimes involved in their formation. Six flows have been identified on the basis of morphological features and systematic three-tier arrangement of vesicular-entablature-colonnade zones. Petrographically, the studied flows are porphyritic basalts with plagioclase and clinopyroxene representing dominant phenocrystal phases. Major and trace element characteristics reflect moderate magmatic differentiation and fractional crystallization of tholeiitic magmas. Chondrite-normalized REE patterns corroborate pronounced LREE/HREE fractionation with LREE enrichment over MREE and HREE. Primitive mantle normalized trace element abundances are marked by LILE-LREE enrichment with relative HFSE depletion collectively conforming to intraplate magmatism with contributions from sub-continental lithospheric mantle (SCLM) and extensive melt-crust interaction. PGE compositions of Vempalle lavas attest to early sulphur-saturated nature of magmas with pronounced sulphide fractionation, while PPGE enrichment over IPGE and higher Pd/Ir ratios accord to the role of a metasomatized lithospheric mantle in the genesis of the lava flows. HFSE-REE-PGE systematics invoke heterogeneous mantle sources comprising depleted asthenospheric MORB type components combined with plume type melts. HFSE-REE variations account for polybaric melting at variable depths ranging from garnet to spinel lherzolite compositional domains of mantle. Intraplate tectonic setting for the Vempalle flows with P-MORB affinity is further substantiated by (i) their origin from a rising mantle plume trapping depleted asthenospheric MORB mantle during ascent, (ii) interaction between plume-derived melts and SCLM, (iii) their rift-controlled intrabasinal emplacement through Archean-Proterozoic cratonic blocks in a subduction-unrelated ocean-continent transition zone (OCTZ). The present study is significant in light of the evolution of Cuddapah basin in the global tectonic framework in terms of its association with Antarctica, plume incubation, lithospheric melting and thinning, asthenospheric infiltration collectively affecting the rifted margin of eastern Dharwar Craton and serving as precursors to supercontinent disintegration.
DS202009-1661
2020
Sjoqvist, A.S.L., Zack, T., Honn, D.K., Baxter, E.F.Modification of a rare-earth element deposit by low temperature partial melting during metamorphic overprinting: Norra Karr alkaline complex, southern Sweden.Chemical Geology, Vol. 545, 13p. PdfEurope, SwedenREE

Abstract: Rare-earth elements play a crucial role in modern technologies and are necessary for a transition to a green economy. Potentially economic deposits of these elements are typically hosted in minerals such as monazite, bastnäsite, and eudialyte (a complex Na-Ca-Fe-Zr silicate mineral with Cl), making these prime targets for geological research. Globally, rare-earth mineral deposits commonly show evidence of polyphase development and mineralisation processes, which need to be better understood to improve exploration strategies. The Norra Kärr alkaline complex (Sweden) contains a globally significant deposit of rare-earth elements, hosted in the mineral eudialyte. In this study, we focussed on eudialyte crystals in undeformed, cross-cutting pegmatoid veins from Norra Kärr. In order to determine their age, we refined an established micromilling method to enable sampling of minerals rich in rare-earth elements for precise analysis of major and trace elements, Nd isotope ratios, and Sm-Nd geochronology down to a scale of <200??m. Mineral samples were subjected to detailed textural and chemical characterisation by backscattered electron imaging and laser ablation inductively coupled plasma mass spectrometry, by which precise and accurate Sm/Nd ratios were determined to steer subsequent micromill sampling for small-aliquot Sm-Nd isotope analysis by isotope dilution thermal ionisation mass spectrometry. Given enough internal spread in Sm/Nd ratios, reliable Sm-Nd isochrons can be derived from discrete textural domains within a single crystal. This provided an age of 1.144?±?0.053?Ga (95% confidence); approximately 350?million?years younger than the magmatic intrusion of the alkaline complex (ca. 1.49?Ga). Primary compositional sector and oscillatory zoning in these eudialyte crystals shows core-to-rim enrichment in rare-earth elements and significant fractionation of K/Rb, Y/Ho, Zr/Hf, and Nb/Ta, which we attribute to crystallisation under influence of complexing ligands in a confined volume. We argue that these mineralised pegmatoid veins formed by low-temperature (<550?°C) partial melting of the agpaitic host rock during an early Sveconorwegian (Grenvillian) metamorphic overprinting event. Given the challenge of directly dating rare-earth ore minerals by conventional methods, modification of rare-earth mineral deposits may be more widespread than already assumed, which shows the importance of investigations that date the rare-earth minerals themselves.
DS202012-2251
2020
Skublov, S.G., Tolstov, A.V., Baranov, L.N., Melnik, A.E., Levashova, E.V.First data on the geochemistry and U-Pb age of zircons from the kamaphorites of the Tomtor alkaline-ultrabasic massif, Arctic Yakutia.Geochemistry , in press available, 11p. PdfRussia, Yakutiadeposit - Tomtor

Abstract: Zircon from Tomtor syenites and kamaphorites was dated following the U-Pb method (SHRIMP-II), and the distribution of trace and rare-earth elements (REE) was studied at the same zircon point using an ion microprobe. The main zircon population from syenites was dated at 402?±?7 Ma, while the age range of single zircon grains was 700-660 M?. Different-aged zircon groups from syenites exhibited the characteristics of magmatic zircon, but their concentrations of REE and other trace elements differed markedly. The REE distribution in 700-660-M? zircon is consistent with that of the typical zircon from syenites (Belousova et al., 2002), while the heavy rare-earth elements (HREE), P, Ti, and Y concentrations of ca. 400-Ma zircon differ from those of older zircon. This is the first isotope-geochemical study of zircon from kamaphorites, and the U-Pb age of ca. 400 M? is within the error limits with of the main zircon population from syenites. The considerable enrichment of REE, C?, Ti, Sr, Y, Nb, and Ba in zircon from kamaphorites may be partly due to the presence of burbankite microinclusions. The trace-element distribution pattern of zircon from kamaphorites is very similar to the geochemical characteristics of zircon from Tiksheozero carbonatites (Tichomirowa et al., 2013). The new age dates for Tomtor syenites and kamaphorites, consistent with 700-660 M? and ca. 400 M? events, support the zircon (Vladykin et al., 2014) and pyrochlore (Antonov et al., 2017) age dates determined following the U-Pb method and those of biotite obtained following the 40Ar-39Ar method (Vladykin et al., 2014).
DS202006-0949
2020
Skvortsova, V.L., Shiryae, A.A., Fedotchouk, Y.Influence of ions on diamond resorption.Diamonds & Related Materials, Vol. 104, 9p. PdfMantlediamond morphology

Abstract: The paper presents a summary of extensive experiments on diamond resorption rates in presence of various ions performed at Prof. Rudenko lab at Moscow State University. For the first time all experimental data are shown together allowing direct comparison. Surface features of the samples etched in different conditions were studied using optical, scanning electron and atomic force microscopy. It is shown that catalytic theory of diamond resorption, a variant of topochemical adsorption theory of crystal etching, explains dramatic differences between activities of ions from different groups of periodic table on diamond resorption rate at least on qualitative level. Strong variations in surface features on diamonds etched in presence of ions with various catalytic activities are observed.
DS202004-0533
2020
Slezak, P., Spandler, C.Petrogenesis of the Gifford Creek carbonatite complex, western Australia.Contributions to Mineralogy and Petrology, Vol. 175, 28p. Pdf.Australiacarbonatite

Abstract: The 1370 Ma Gifford Creek Carbonatite Complex (GCCC) comprises a diverse suite of alkaline dyke and sill complexes that cover an area of?~?250 km2 in the Gascoyne Province, Western Australia. Most carbonatite types are interpreted to be related products of fractional crystallisation, with calcite carbonatites representing cumulate rocks and dolomite carbonatites representing crystallised products of the derivative liquids. Genetic relationships between these carbonatites and other alkaline igneous units are less clear. The ankerite-siderite carbonatites and magnetite-biotite dykes are likely of related magmatic origin as both have distinctly high LREE and low HFSE contents. The ankerite-siderite carbonatites have mantle-like ?13C isotope values of ? 6.1 to ? 7.1‰ and similar geochemistry to other known magmatic ferrocarbonatites. Silica-rich alkaline veins found near the centre of the complex have trace element signatures that are antithetic to the magnetite-biotite dykes, so these veins are interpreted to represent products of alkali- and F-rich magmatic-hydrothermal fluids exsolved from the magnetite-biotite dykes during their emplacement. Carbon, O, Sr, and Nd isotope data are consistent with an enriched mantle source for the origin of the GCCC, with mantle enrichment likely caused by plate convergence processes associated with the c. 2.0 Ga Glenburgh Orogeny. There is no evidence to link mantle plume activity with formation of the GCCC; rather, alkaline magmatism is interpreted to result from low degree melting of the metasomatised mantle during reactivation of the crustal suture zone at 1370 Ma. The carbonatitic magmas utilised the Lyons River Fault to traverse the crust to be emplaced as the GCCC. Post magmatic alteration has variably modified the O and Sr isotope compositions of carbonates from these rocks. We therefore appeal for careful evaluation of isotopic data from ancient carbonatites, as isotopic resetting may be more common than currently recognised.
DS202008-1444
2020
Smit, K.V., Pearson, D.G., Krebs, M.Y., Woodland, S.Trace elements of rare CH4-bearing fluids in Zimbabwe diamonds.Goldschmidt 2020, 1p. AbstractAfrica, Zimbabwedeposit - Marange

Abstract: Marange diamonds (Zimbabwe) contain both fluid-poor (gem-quality) and fluid-bearing growth zones with abundant CH4. As such, they provide the unique opportunity to compare trace element compositions of CH4-bearing diamonds with those of carbonatitic and saline high density fluid (HDF)-bearing diamonds (gem-quality and fibrous) to obtain an overview of mantle source fluids for diamond growth. HDF’s in fibrous diamonds and some gem-quality diamonds have been linked to subduction of surficial material, consistent with the global link between diamond age and collisional tectonic events. Even though Marange diamonds have +?15N indicative of surficial recycling, they do not display the expected Eu or Sr anomalies. Fibrous diamonds have the most fractionated REE patterns, with negligible HREE and high (La/Yb)N ? 100- 10000. Gem-quality diamonds have highly variable (La/Yb)N; the most unfractionated HDF’s are in Victor and Cullinan diamonds with low (La/Yb)N <76. HDF’s in Marange diamonds are intermediate between these two extremes, with (La/Yb)N = 23-240. Differences in (La/Yb)N between different diamond suites relate either to varying initial compositions (where low (La/Yb)N reflects derivation during higher degrees of melting) or to the increasing interaction of HDF’s in fibrous diamonds with mantle rocks during fluid infiltration. Marange diamonds have rare +Ce anomalies, that have so far only been reported for Victor and Brazil (sub-lithospheric) gem-quality diamonds. The oxidation state of Ce (Ce4+ vs Ce3+) and development of Ce anomalies could be attributed to ƒO2, melt/fluid composition, and PT conditions. In Marange, Victor and Brazil diamonds, Ce4+ substitution for Zr4+ does not appear to be a factor since we find no correlation between Zr content and Ce anomalies. However, in Marange diamonds, CH4-bearing zones have less variable Ce anomalies compared to the CH4-free zones, which may suggest Ce anomalies are indicative of fluid oxidation state.
DS202008-1445
2020
Smit, K.V., Shirey, S.B.Diamonds are not forever! Diamond dissolution. ( mentions Letlhakane, Ekati, Diavik, Snap Lake), transport, storage, time scales, resorption, fluids, trigonsGems & Gemology, Vol. 56, 1, pp. 148-155.MantleCrystallography

Abstract: Before cutting and polishing, diamonds have highly variable surface features rarely, if ever, seen by the jewelry wearer. These features can tell an interesting story of diamond’s geological history deep within Earth-both in the mantle rocks where diamonds grew and during their subsequent volcanic transport. Our previous column showed that volcanic eruptions of kimberlite are how diamonds make their way from depth in the mantle to Earth’s surface. But this violent process does not leave the rough diamond unscathed. These early histories are rarely considered once the diamond has been faceted and set into jewelry, but they raise interesting and geologically important questions: Why do rough diamonds look so different from each other, and what might this tell us about their geological history? What effect does the kimberlite magma have on the diamond cargo? How can we see through this later stage of the diamond’s history to its millions and billions of years of mantle storage?
DS202005-0762
2020
Smith, D.Trace elements in Cr-pyrope from the Navajo volcanic field of the Colorado Plateau, SW USA, and implications for the mantle wedge during low angle subduction.Lithos, doi.org/10.101016/j. lithos.2020.105460, 55p. PdfUnited States, Coloradosubduction

Abstract: The zonation of trace elements in Cr-pyrope has been analyzed to investigate histories recorded by garnet in cool mantle and implications for processes in the mantle wedge during low-angle subduction. The garnets are from the Navajo Volcanic Field (NVF) of the Colorado Plateau in the southwestern United States. Their host rocks were emplaced between 30 and 24 Ma, not long after low-angle subduction of the Farallon plate and the Laramide orogeny. Twenty-seven of the 31 garnets are discrete fragments from diatremes of serpentinized ultramafic microbreccia (SUM). Many Ni and Mn values in those grains yield temperatures in and below the range 800 °C to 600 °C, consistent with inclusions of chlorite and other hydrous minerals. Gradients of Na, Ti, Mn, Ni, Y, REE, and other elements are common in the discrete grains. Diffusion calculations constrain possible histories of a garnet with growth zonation of Y and REE and retrograde zonation of Mn and Ni. The garnet must have formed and resided at temperatures below about 900 °C, and that zonation is unlikely to have been preserved from the Proterozoic. The Mn gradient is consistent with cooling during the time period of low-angle Farallon subduction. Many of the discrete garnets grew from sources metasomatically enriched in Li, Na, Ti, and Zr, and they have distinctive high Li/Na. The high Li/Na is a likely consequence of Li metasomatism in the mantle wedge. Nb values in the Cr-pyrope fragments from northern SUM diatremes are lower than those of most garnets from kimberlites, but the low values are similar to and lower than those of pyrope in peridotite emplaced in orogenic belts; those northern diatremes also host lawsonite eclogite and garnetite. Most but not all relatively Cr-rich discrete garnets (4 to 8 wt% Cr2O3) record enrichment in LREE but little enrichment in Ti and Zr; LREE enrichment by an aqueous fluid is consistent with chlorite inclusions in two of these garnets. Oriented lamellae of rutile and other phases are common, and one texture may record fluid interactions associated with interface-coupled dissolution-reprecipitation. Garnets from the four minette-hosted peridotites record markedly hotter temperatures than do the SUM-hosted grains, and they lack the high Li/Na and low Nb. Gradients of trace elements in minette-hosted garnets record metasomatism shortly before crustal emplacement, but that metasomatism resulted in a decrease of Nb and had little effect on Li/Na. The minette-hosted garnet peridotites may represent mantle residual from Proterozoic accretion of the Colorado Plateau. In contrast, at least some of the SUM-hosted garnets probably grew in rock eroded from the forearc wedge by low-angle subduction and emplaced below the NVF.
DS202008-1446
2020
Smith, E.How the biggest and best diamonds defy exploration.https://www.youtube.com/watch?.V=VWt4FSESJ84&feature=youtu.be, 38pptsGlobalCLIPPIR
DS202008-1447
2020
Smith, E.Shorter version 5 minshttps://youtu.be/n_un9NfeG90, ?GlobalCLIPPIR
DS202009-1662
2020
Smith, E.How the biggest and best diamonds defy exploration.Ore Deposits Hub You Tube ODH029, https://youtu.be/vwt4FSESI84GlobalCLIPPER
DS202009-1663
2020
Smith, E.M., Nestola, F., Pasqualetto, L., Zorzi, F., Secco, L., Wang, W.The new mineral crowningshieldite: a high temperature NiS polymorph found in a type IIa diamond from the Letseng mine, Lesotho.The American Mineralogist, in press available, 33p. PdfAfrica, Lesothodeposit - Letseng
DS202008-1448
2020
Smith, E.M., Wang, W.New insights into sublithospheric Type IIa and type IIb diamonds.Goldschmidt 2020, 1p. AbstractMantleCLIPPIR

Abstract: In the past few years, two new diamond varieties have been characterized as sublithospheric, or super-deep, in origin. Ongoing studies of new inclusion-bearing specimens continue to improve our understanding of type IIa (more specifically, CLIPPIR) and type IIb diamonds. CLIPPIR diamonds are a variety epitomized by large and high quality type IIa gem diamonds, such as the 3106 carat Cullinan diamond [1]. Among their inclusions are examples of majoritic garnet and inferred CaSiO3-perovskite, suggesting a formation depth in the range of 360 to 750 km [1, 2]. Type IIb diamonds (boron-bearing) host inclusions of ferropericlase as well as retrogressed majoritic garnet, CaSiO3-perovskite, CF-type phase, stishovite, and bridgmanite [3]. The mineral assemblage suggests an origin deeper than 360 km, likely in the transition zone to uppermost lower mantle. The relationship between these two similar diamond varieties remains somewhat unclear. Studies to date have left open the possibility that CLIPPIR diamonds might be formed at distinctly shallower depths than type IIb’s, without any overlap. An additional large (>100 carats) rough CLIPPIR diamond has now been examined that contains inclusions of retrogressed aluminous bridgmanite. This is the first evidence of CLIPPIR diamond growth in the lower mantle, meaning there must be some overlap between the depth of formation for CLIPPIR and type IIb diamonds. A related issue concerning depth of formation, for type IIb diamonds [4], has also been addressed by examination of a new specimen. A large (>10 ct) type IIb diamond has been found to contain former bridgmanite, which helps to dissolve the apparent dichotomy between inclusions in larger (>2ct) and smaller (<2ct) type IIb diamonds [4, 5]. These recently examined specimens are helping to build a clearer picture of the paragenesis and geochemical implciations of these exquisite gem diamonds.
DS202001-0040
2019
Smithies, R.H., Lu, Y., Johnson, T.E., Kirkland, C.L., Cassidy, K.F., Champion, D.C., Mole, D.R., Zibra, I., Gessner, K., Sapkota, J., De Paoli, M.C., Poujol, M.No evidence for high pressure melting of Earth's crust in the Archean.Nature Communicatons, Vol. 10, 555912p. PdfAustraliamelting

Abstract: Much of the present-day volume of Earth’s continental crust had formed by the end of the Archean Eon, 2.5 billion years ago, through the conversion of basaltic (mafic) crust into sodic granite of tonalite, trondhjemite and granodiorite (TTG) composition. Distinctive chemical signatures in a small proportion of these rocks, the so-called high-pressure TTG, are interpreted to indicate partial melting of hydrated crust at pressures above 1.5?GPa (>50?km depth), pressures typically not reached in post-Archean continental crust. These interpretations significantly influence views on early crustal evolution and the onset of plate tectonics. Here we show that high-pressure TTG did not form through melting of crust, but through fractionation of melts derived from metasomatically enriched lithospheric mantle. Although the remaining, and dominant, group of Archean TTG did form through melting of hydrated mafic crust, there is no evidence that this occurred at depths significantly greater than the ~40?km average thickness of modern continental crust.
DS202010-1878
2020
Smyth, D.Petrology, geochemistry, and geochronology of the Pikoo kimberlites, Saskatchewan.Thesis, Msc. University of Alberta, 245p. PdfCanada, Saskatchewandeposit - Pikoo

Abstract: The Pikoo kimberlites of east-central Saskatchewan are a relatively recent discovery, comprising at least ten discreet bodies thought to erupt through the Sask Craton, a small Archean microcontinent enclosed within the Paleoproterozoic Trans-Hudson Orogen. Since the Sask Craton also plays host to the 70+ bodies of the diamondiferous Cretaceous Fort à la Corne kimberlites, which are among the largest kimberlites in the world, significant interest lay in unraveling the genesis of the Pikoo bodies. This study presents the first detailed examination of the petrology and geochronology of the Pikoo kimberlites. A combination of detailed petrography, major and minor element chemistry analyzed by EPMA, and trace element determinations measured via LA-ICP-MS was employed to characterize the Pikoo samples as archetypal coherent (hypabyssal) kimberlite. Traditional criteria for diamond preservation potential were applied to the Pikoo ilmenite by assessing their Fe2O3 and MgO contents. The results indicated high MgO and low Fe2O3 within the grain interiors and rims with elevated MgO and MnO in PK150, PK151, PK314, and variably in PK312. The high-Fe mineral compositions of PK346 contradict the trends of the other intrusions, suggesting PK346 formed from an oxidized, high-carbonate late pulse of previously fractionated magma. The differences in magma evolution can explain the striking petrographic and chemical distinctions highlighted between the two most significant intrusions of PK150 and PK346, as well as the notably less favourable microdiamond results North Arrow reported for PK346. A robust U-Pb age of 417 ± 14 Ma was determined from PK150 perovskite analyzed in situ via LA-ICP-MS. The data were processed using two approaches to confirm the perovskite represented a single population with a uniform common Pb composition. This age is distinctly different from the nearby FALC kimberlites but overlaps with occurrences in the Slave Craton, the United States, Russia, and Namibia. This may suggest more widespread diamond-bearing kimberlite activity in circa Silurian times. Tracer isotopes were also measured in situ via LA-MC-ICP-MS on PK150 perovskite. The dominant range in ?Ndi (+1.8 to -2.0) is near chondritic, suggesting a deep mantle source isolated from contamination.
DS202008-1449
2020
Sokol, I.A., Sokol, A.G., Zaikin, P.A., Tomilenko, A.A., Bulbak, T.A.Hydrogenation of graphite, diamond, carbonates and iron carbides as the source of hydrocarbons in the upper mantle.Goldschmidt 2020, 1p. AbstractMantlehydrogen

Abstract: Formation of hydrocarbons by reactions of hydrogenbearing fluids with carbon [1] (13C soot, graphite, or diamond), carbonate-bearing pelites [2] and iron carbides (Fe3C and Fe7C3) [3] was simulated at 5.5-7.8 GPa and 1100- 1400°C, fH2 in Pt and Au capsules being controlled at the Mo+MoO2+H2O or Fe+FeO+H2O equilibria. For the first time, formation of hydrocarbons from inorganic compounds was proved by the reaction of 13C with hydrogen, which yielded isotopically pure alkanes. The greatest amounts of HCs (CH4/C2H6 < 1, CH4/C3H8 and CH4/C4H10 ? 10) formed at 1400°C in the 10-hr run. The amount of HCs synthesized at 1200°C was twice smaller. The rate of HCs formation was slowest in runs with diamond. At 1200 °C, light alkanes (C1?C2>C3>C4) formed either by direct hydrogenation of Fe3C or Fe7C3, or by hydrogenation of graphite/diamond in the presence of Fe3C, Fe7C3. The CH4/C2H6 ratio in the fluids decreased from 5 to 0.5 with decreasing iron activity and the C fraction increased in the series: Fe-Fe3C?Fe3C- Fe7C3?Fe7C3-graphite?graphite-Fe3C-magnesite and Fe3C-H2O-CO2 systems at 1200 °C yielded magnesiowüstite and wüstite, respectively, and both produced C-rich Fe7C3 and mainly light alkanes (C1?C2>C3>C4). In the experiments containing pelites methaneimine (CH3N) was found to be the main N-bearing compound. The experiments have provided the first unambiguous evidence that volatile-rich and reduced mantles of terrestrial planets (at fO2 near or below IW) provided favorable conditions for abiotic generation of complex hydrocarbon systems that predominantly contain light alkanes. The conditions favorable for HC formation exist in earth mantle, where slab-derived H2O-, CO2- and carbonate-bearing fluids interact with metal-saturated mantle.
DS202007-1178
2020
Soltys, A., Giuliani, A,m Phillips, D., Kamenetsky, V.S.Kimberlite metasomatism of the lithosphere and the evolution of olivine in carbonate rich melts evidence from the Kimberley kimberlites ( South Africa).Journal of Petrology, 10.1093/petrology /egaa062/5857610 90p. PdfAfrica, South Africadeposit - Kimberley

Abstract: Olivine is the most abundant phase in kimberlites and is stable throughout most of the crystallisation sequence, thus providing an extensive record of kimberlite petrogenesis. To better constrain the composition, evolution, and source of kimberlites we present a detailed petrographic and geochemical study of olivine from multiple dyke, sill, and root zone kimberlites in the Kimberley cluster (South Africa). Olivine grains in these kimberlites are zoned, with a central core, a rim overgrowth, and occasionally an external rind. Additional ‘internal’ and ‘transitional’ zones may occur between the core and rim, and some samples of root zone kimberlites contain a late generation of high-Mg olivine in cross-cutting veins. Olivine records widespread pre-ascent (proto-)kimberlite metasomatism in the mantle including: (a) Relatively Fe-rich (Mg# <89) olivine cores interpreted to derive from the disaggregation of kimberlite-related megacrysts (20% of cores); (b) Mg-Ca-rich olivine cores (Mg# >89; >0.05?wt.% CaO) suggested to be sourced from neoblasts in sheared peridotites (25% of cores); (c) transitional zones between cores and rims probably formed by partial re-equilibration of xenocrysts (now cores) with a previous pulse of kimberlite melt (i.e., compositionally heterogeneous xenocrysts); and (d) olivine from the Wesselton water tunnel sills, internal zones (I), and low-Mg# rims, that crystallised from a kimberlite melt that underwent olivine fractionation within the shallow lithospheric mantle. Magmatic crystallisation begins with internal olivine zones (II), which are common but not ubiquitous in the Kimberley olivine. These zones are euhedral, contain rare inclusions of chromite, and have a higher Mg# (90.0 ± 0.5), NiO, and Cr2O3 contents, but are depleted in CaO compared to the rims. Internal olivine zones (II) are interpreted to crystallise from a primitive kimberlite melt during its ascent and transport of olivine toward the surface. Their compositions suggest assimilation of peridotitic material (particularly orthopyroxene) and potentially sulfides prior to or during crystallisation. Comparison of internal zones (II) with liquidus olivine from other mantle-derived carbonate-bearing magmas (i.e., orangeites, ultramafic lamprophyres, melilitites) show that low (100×) Mn/Fe (?1.2), very low Ca/Fe (?0.6), and moderate Ni/Mg ratios (?1.1) appear to be the hallmarks of olivine in melts derived from carbonate-bearing garnet-peridotite sources. Olivine rims display features indicative of magmatic crystallisation, which are typical of olivine rims in kimberlites worldwide - i.e. primary inclusions of chromite, Mg-ilmenite and rutile, homogeneous Mg# (88.8 ± 0.3), decreasing Ni and Cr, increasing Ca and Mn. Rinds and high-Mg olivine are characterised by extreme Mg-Ca-Mn enrichment and Ni depletion, and textural relationships indicate these zones represent replacement of pre-existing olivine, with some new crystallisation of rinds. These zones likely precipitated from evolved, oxidised, and relatively low-temperature kimberlite fluids after crustal emplacement. In summary, this study demonstrates the utility of combined petrography and olivine geochemistry to trace the evolution of kimberlite magmatic systems from early metasomatism of the lithospheric mantle by (proto-)kimberlite melts, to crystallisation at different depths en route to surface, and finally late-stage deuteric/hydrothermal fluid alteration processes after crustal emplacement.
DS202006-0950
2020
Soltys, A., Giuliani, A., Phillips, D.Apatite compositions and groundmass mineralogy record divergent melt/fluid evolution trajectories in coherent kimberlites caused by differing emplacement mechanisms.Contributions to Mineralogy and Petrology, Vol. 175, 21p. PdfAfrica, South Africadeposit - Kimberley

Abstract: Kimberlites are pipe-like igneous bodies, consisting of a pyroclastic crater and diatreme, commonly underlain by coherent root-zone rocks, and with associated dyke/sill complexes. The processes that control the different modes of coherent kimberlite emplacement remain uncertain. In addition, late evolution of kimberlite melts during emplacement into the upper crust remains poorly constrained. Therefore, it is unclear whether there is a link between melt composition/evolution and the emplacement mechanism of coherent kimberlites (i.e. planar dykes/sills vs. irregular bodies in the root zone). An absence of comparative studies on late-stage magmatic phases across the different emplacement modes of coherent kimberlite from the same locality hamper resolution of these issues. Therefore, we report petrographic and mineral chemical data for groundmass apatite in samples of dyke, sill, and root-zone kimberlites from the Kimberley cluster (South Africa). Early crystallised phases (olivine, spinel, Mg-ilmenite) in dyke/sill and root-zone kimberlites have indistinguishable compositions, and hence crystallised from similar primitive melts. Conversely, apatite compositions are generally distinct in dyke/sill (low Sr, high and variable Si) and root-zone kimberlites (high and variable Sr, low Si). The Si enrichment of apatite in dykes/sills is attributed to the coupled incorporation of CO32? and SiO44? for PO43?, reflecting higher CO2 contents in their parental melts, and potentially higher Si contents due to the preferential crystallisation of carbonates over mica/monticellite. The low Sr contents of apatite in dyke/sill kimberlites reflect equilibrium with a (kimberlite) melt (i.e. DSr is close to unity for carbonate and silicate melts), whereas the higher Sr contents of apatite in root-zone kimberlites require crystallisation from, or overprinting by a H2O?±?CO2 fluid (significantly higher DSr). The relative enrichment of CO2 in kimberlite dykes/sills is evident from the abundance of carbonates, the presence of mesostasis dolomite and calcite phenocrysts in some samples, and concomitant reduced proportions of other groundmass phases (e.g. serpentine, mica, monticellite). During late alteration of kimberlite dykes/sills, monticellite is typically replaced by carbonates, whereas olivine and pleonaste are relatively stable, indicating the melts which form dykes/sills evolve to higher CO2/H2O ratios. It is unlikely that these two distinct evolutionary paths were caused by crustal contamination before or during near surface magma emplacement, because crustal assimilation is not recorded in the O and Sr isotopic composition of late crystallising olivine rinds or carbonates, respectively. We suggest that higher concentrations of CO2 are retained in kimberlite dykes/sills due to higher confining pressures (i.e. lack of breakthrough to the surface). In contrast, exsolution of CO2 from root-zone kimberlites increased melt H2O/CO2 ratios and promoted the crystallisation of mica and monticellite at the expense of dolomite and calcite. Apatite compositions have the potential to aid in the discrimination of kimberlites from lamproites (higher LREE, Sr, F, and S, lower Si contents) and carbonatites (higher LREE, F, Cl and S, lower Fe contents). However, the compositions of kimberlitic apatite overlap those from aillikites, probably due to similar late-stage melt compositions.
DS202007-1179
2020
Soltys, A., Giuliani, A., Phillips, D.Apatite compositions and groundmass mineralogy record divergent melt/fluid evolution trajectories in coherent kimberlites caused by differing emplacement mechanisms.Contributions to Mineralogy and Petrology, Vol. 175, 49 dor.org./10.1007 /s00410-020-01686-0Africa, South Africadeposit - Kimberley

Abstract: Kimberlites are pipe-like igneous bodies, consisting of a pyroclastic crater and diatreme, commonly underlain by coherent root-zone rocks, and with associated dyke/sill complexes. The processes that control the different modes of coherent kimberlite emplacement remain uncertain. In addition, late evolution of kimberlite melts during emplacement into the upper crust remains poorly constrained. Therefore, it is unclear whether there is a link between melt composition/evolution and the emplacement mechanism of coherent kimberlites (i.e. planar dykes/sills vs. irregular bodies in the root zone). An absence of comparative studies on late-stage magmatic phases across the different emplacement modes of coherent kimberlite from the same locality hamper resolution of these issues. Therefore, we report petrographic and mineral chemical data for groundmass apatite in samples of dyke, sill, and root-zone kimberlites from the Kimberley cluster (South Africa). Early crystallised phases (olivine, spinel, Mg-ilmenite) in dyke/sill and root-zone kimberlites have indistinguishable compositions, and hence crystallised from similar primitive melts. Conversely, apatite compositions are generally distinct in dyke/sill (low Sr, high and variable Si) and root-zone kimberlites (high and variable Sr, low Si). The Si enrichment of apatite in dykes/sills is attributed to the coupled incorporation of CO32? and SiO44? for PO43?, reflecting higher CO2 contents in their parental melts, and potentially higher Si contents due to the preferential crystallisation of carbonates over mica/monticellite. The low Sr contents of apatite in dyke/sill kimberlites reflect equilibrium with a (kimberlite) melt (i.e. DSr is close to unity for carbonate and silicate melts), whereas the higher Sr contents of apatite in root-zone kimberlites require crystallisation from, or overprinting by a H2O?±?CO2 fluid (significantly higher DSr). The relative enrichment of CO2 in kimberlite dykes/sills is evident from the abundance of carbonates, the presence of mesostasis dolomite and calcite phenocrysts in some samples, and concomitant reduced proportions of other groundmass phases (e.g. serpentine, mica, monticellite). During late alteration of kimberlite dykes/sills, monticellite is typically replaced by carbonates, whereas olivine and pleonaste are relatively stable, indicating the melts which form dykes/sills evolve to higher CO2/H2O ratios. It is unlikely that these two distinct evolutionary paths were caused by crustal contamination before or during near surface magma emplacement, because crustal assimilation is not recorded in the O and Sr isotopic composition of late crystallising olivine rinds or carbonates, respectively. We suggest that higher concentrations of CO2 are retained in kimberlite dykes/sills due to higher confining pressures (i.e. lack of breakthrough to the surface). In contrast, exsolution of CO2 from root-zone kimberlites increased melt H2O/CO2 ratios and promoted the crystallisation of mica and monticellite at the expense of dolomite and calcite. Apatite compositions have the potential to aid in the discrimination of kimberlites from lamproites (higher LREE, Sr, F, and S, lower Si contents) and carbonatites (higher LREE, F, Cl and S, lower Fe contents). However, the compositions of kimberlitic apatite overlap those from aillikites, probably due to similar late-stage melt compositions.
DS202009-1664
2020
Soltys, A., Giuliani, A., Phillips, D., Kamenetsky, V.S.Kimberlite metasomatism of the lithosphere and the evolution of olivine in carbonate rich melts - evidence from the Kimberley kimberlites ( South Africa).Journal of Petrology, in press available, 90p. PdfAfrica, South Africadeposit - Kimberley

Abstract: Olivine is the most abundant phase in kimberlites and is stable throughout most of the crystallization sequence, thus providing an extensive record of kimberlite petrogenesis. To better constrain the composition, evolution, and source of kimberlites we present a detailed petrographic and geochemical study of olivine from multiple dyke, sill, and root zone kimberlites in the Kimberley cluster (South Africa). Olivine grains in these kimberlites are zoned, with a central core, a rim overgrowth, and occasionally an external rind. Additional ‘internal’ and ‘transitional’ zones may occur between the core and rim, and some samples of root zone kimberlites contain a late generation of high-Mg olivine in cross-cutting veins. Olivine records widespread pre-ascent (proto-)kimberlite metasomatism in the mantle including the following features: (1) relatively Fe-rich (Mg# <89) olivine cores interpreted to derive from the disaggregation of kimberlite-related megacrysts (20?% of cores); (2) Mg-Ca-rich olivine cores (Mg# >89; >0•05?wt% CaO) suggested to be sourced from neoblasts in sheared peridotites (25?% of cores); (3) transitional zones between cores and rims probably formed by partial re-equilibration of xenocrysts (now cores) with a previous pulse of kimberlite melt (i.e. compositionally heterogeneous xenocrysts); (4) olivine from the Wesselton water tunnel sills, internal zones (I), and low-Mg# rims, which crystallized from a kimberlite melt that underwent olivine fractionation and stalled within the shallow lithospheric mantle. Magmatic crystallization begins with internal olivine zones (II), which are common but not ubiquitous in the Kimberley olivine. These zones are euhedral, contain rare inclusions of chromite, and have a higher Mg# (90•0 ± 0•5), NiO, and Cr2O3 contents, but are depleted in CaO compared with the rims. Internal olivine zones (II) are interpreted to crystallize from a primitive kimberlite melt during its ascent and transport of olivine toward the surface. Their compositions suggest assimilation of peridotitic material (particularly orthopyroxene) and potentially sulfides prior to or during crystallization. Comparison of internal zones (II) with liquidus olivine from other mantle-derived carbonate-bearing magmas (i.e. orangeites, ultramafic lamprophyres, melilitites) shows that low (100×) Mn/Fe (?1•2), very low Ca/Fe (?0•6), and moderate Ni/Mg ratios (?1•1) appear to be the hallmarks of olivine in melts derived from carbonate-bearing garnet-peridotite sources. Olivine rims display features indicative of magmatic crystallization, which are typical of olivine rims in kimberlites worldwide; that is, primary inclusions of chromite, Mg-ilmenite and rutile, homogeneous Mg# (88•8 ± 0•3), decreasing Ni and Cr, and increasing Ca and Mn. Rinds and high-Mg olivine are characterized by extreme Mg-Ca-Mn enrichment and Ni depletion, and textural relationships indicate that these zones represent replacement of pre-existing olivine, with some new crystallization of rinds. These zones probably precipitated from evolved, oxidized, and relatively low-temperature kimberlite fluids after crustal emplacement. In summary, this study demonstrates the utility of combined petrography and olivine geochemistry to trace the evolution of kimberlite magmatic systems from early metasomatism of the lithospheric mantle by (proto-)kimberlite melts, to crystallization at different depths en route to surface, and finally late-stage deuteric or hydrothermal fluid alteration after crustal emplacement.
DS202010-1879
2020
Song, Z., Lu, T., Liu, H., Dai, H., Ke, J., Zhu, W., Zhang, J.Identification of Type IIa blue CVD diamonds from Huzhou SinoC semiconductor.Journal of Gemmology, Vol. 37, 3, pp. 306-313.Chinasynthetics

Abstract: Gemmological and spectroscopic characteristics are reported for two type IIa blue CVD synthetic diamonds from Huzhou SinoC Semiconductor Science and Technology Co. Ltd, China. These are the first relatively large (1.76 and 2.63 ct) blue CVD synthetics examined in NGTC’s laboratories, and their colour was slightly brighter than other blue synthetic diamonds that we have encountered. In the DiamondView, they fluoresced blue (with purple-red in one sample), which is unusual for CVD synthetics. The mid- and near-IR absorption spectra of one sample showed no hydrogen-related features, while the other synthetic diamond showed a weak absorption at 6853 cm?1attributed to hydrogen. The spectra of both samples had a very weak line at 1332 cm?1 due to isolated nitrogen and a distinct band at 9282 cm-1 related to radiation. A very strong GR1 absorption feature was detected by UV-Vis-NIR spectroscopy. Photoluminescence spectra obtained at liquid-nitrogen temperature recorded emissions related to radiation (mainly in the 480-510 nm region), N-V and [Si-V]- centres, and several unassigned weak emissions. This combination of optical centres strongly suggests that these samples underwent post-growth treatment to improve their transparency before they were irradiated to produce blue colouration.
DS202002-0218
2019
Sonin, V., Leech, M., Chepurov, A., Zhimulev, E., Chepurov, A.Why are diamonds preserved in UHP metamorphic complexes? Experimental evidence for the effect of pressure on diamond graphitization.International Geology Review, Vol. 61, 4, pp. 504-519.Russia, Chinacoesite, UHP

Abstract: The preservation of metastable diamond in ultrahigh-pressure metamorphic (UHPM) complexes challenges our understanding of the processes taking place during exhumation of these subduction zone complexes. The presence of diamonds in UHPM rocks implies that diamonds remained metastable during exhumation, and within thermodynamic stability of graphite for an extended period. This work studies the influence of pressure on the surface graphitization rate of diamond monocrystals in carbonate systems to understand the preservation of microdiamond during exhumation of UHP subduction complexes. Experiments were performed with 2-3 mm synthetic diamond monocrystals at 2-4 GPa in ????3 (1550°?) and ?2??3 (1450°?) melts using a high-pressure multi-anvil apparatus. The highest rate of surface graphitization took place at 2 GPa; diamond crystals were almost completely enveloped by a graphite coating. At 4 GPa, only octahedron-shaped pits formed on flat {111} diamond crystal faces. Our results demonstrate that the surface graphitization rate of diamonds in the presence of carbonate melts at 1450-1550°C increases with decreasing pressure. Decreased pressure alone can graphitize diamond regardless of exhumation rate. Metastable diamond inclusions survive exhumation with little or no graphitization because of excess pressure up to 2 GPa acting on them, and because inclusions are protected from interaction with C-O-H fluid.
DS202010-1880
2020
Sonin, V.M., Tomilenko, A.A., Zhimulev, E.I., Bulbak, T.A., Timina, T.Y., Chepurov, A.I., Pokhilenko, N.P.Diamond crystallization at high pressure: the relative efficiency of metal graphite and metal carbonate systems.Doklady Earth Sciences, Vol. 493, 1, pp. 508-512.RussiaUHP

Abstract: Data on the interaction of the Fe-Ni melt with CaCO3 and graphite at 5 GPa and 1400°? under the thermogradient conditions used in experiments on the growth of diamond on the BARS high-pressure apparatus are presented. The phase composition and component composition of the fluid captured by diamonds in the form of inclusions were studied by gas chromatography-mass spectrometry (GC-MS). Diamonds were synthesized from graphite. During the interaction of the Fe-Ni melt with CaCO3, Ca-Fe oxides and (Fe, Ni)3C carbide were formed. The stability of heavy hydrocarbons under the experimental conditions was confirmed. It was established that the composition of the fluid in synthesized diamonds is close to the composition of the fluid from inclusions in some natural diamonds. Nevertheless, it was concluded that crystallization of large diamonds under natural conditions is hardly possible due to the filling of the main crystallization volume with refractory oxide phases.
DS202001-0041
2019
Sorokhtina, N.V., Kogarko, L.N., Zaitsev, V.A., Kononkova, N.N., Asavin, A.M.Sulfide mineralization in the carbonatites and phoscorites of the Guli Massif, Polar Siberia, and their noble metal potential.Geochemistry International, Vol. 57, 11, pp. 1125-1146.Russia, Siberiacarbonatite

Abstract: We report the first combined investigation (neutron activation, X-ray fluorescence, and electron microprobe analysis) of mineral forms of Au and Ag and noble metal distribution in the sulfide-bearing phoscorites and carbonatites of the Guli alkaline ultrabasic massif (Polar Siberia) and magnetite and sulfide separates from these rocks. The highest noble metal contents were observed in the sulfide separates from the carbonatites: up to 2.93 Pt, 61.6 Au, and 3.61 ppm Ag. Pyrrhotite, djerfisherite, chalcopyrite, and pyrite are the most abundant sulfides and the main hosts for Au and Ag. The latest assemblage of chalcopyrite, Ag-rich djerfisherite, lenaite, sternbergite, and native silver shows significant Ag concentrations. The wide occurrence of K sulfides and presence of multiphase inclusions in pyrrhotite consisting of rasvumite, K?Na–Ca carbonate, carbocernaite, strontianite, galena, chalcopyrite, sternbergite, lenaite, and native silver suggest that the sulfides were formed at high activities of K, Na, Sr, LREE, F, Cl, and S. Chlorine shows high complex-forming capacity to Ag and could be an agent of noble metal transport in the carbonatites. Crystallization of the early djerfisherite–pyrrhotite assemblages of the phoscorites and carbonatites began at a temperature not lower than 500°C and continued up to the formation of late Ag-bearing sulfides at temperatures not higher than 150°C. The carbonatite-series rocks could be enriched in Au and Ag during late low-temperature stages and serve as a source for Au placers.
DS202007-1180
2020
Spandler, C., Slezak, P., Nazari-Dehkordi, T.Tectonic significance of Australian rare earth element deposits.Earth Science Reviews, Vol. 207, 103219 16p. PdfAustraliaREE

Abstract: Australia is host to a diverse range of rare earth element (REE) ore deposits, and therefore is well placed to be a major supplier of REE into the future. This paper presents a review of the geology and tectonic setting of Australia's hard-rock REE resources. The deposits can be classified into four groups: 1. Carbonatite associated; 2. Peralkaline/alkaline volcanic associated; 3. Unconformity related, and; 4. Skarns and iron-oxide?copper?gold (IOCG) related. With the exception of the unconformity related deposits, all of these deposit groups are directly or indirectly related to continental alkaline magmatism. Extensive fractional crystallisation and/or igneous accumulation of REE minerals were essential ore-forming processes for carbonatite-associated and peralkaline/alkaline volcanic-associated deposits, while hydrothermal transport and concentration of REE sourced from basement rocks was responsible for producing ore in unconformity-related, skarns and, potentially, IOCG deposits. The economic potential of many deposits has also been enhanced by supergene alteration processes. All of Australia's REE deposits formed in an intracontinental setting in association with crustal-scale fault zones or structures that acted as transport conduits for ore-forming magmas or fluids. Most deposits formed in the Mesoproterozoic under conditions of relative tectonic quiescence. There is little evidence for the involvement of mantle plumes, with the exception of the Cenozoic peralkaline volcanic systems of eastern Australia, and possibly the IOCG deposits. Instead, ore productive magmas were generated by melting of previously-enriched mantle lithosphere in response to disruption of the lithosphere-asthenophere boundary due to fault activation. REE minerals in many deposits also record episodes of recrystallisation/resetting due to far-field effects of orogenic activity that may significantly postdate primary ore formation. Therefore, REE orebodies can be effective recorders of intracontinental deformation events. In general, Australia's inventory of REE deposits is similar to the global record. Globally, the Mesoproterozoic appears to be a particularly productive time period for forming REE orebodies due to favourable conditions for generating ore-fertile magmas and favourable preservation potential due to a general lack of aggressive continental recycling (i.e., active plate tectonics).
DS202011-2061
2020
Speciale, S., Censi, P., Gomes, C., Marques, L.Carbonatites from the southern Brazilian platform: a review. II: isotopic evidences.Open Geosciences ( researchgate), 26p. PdfSouth America, Brazilcarbonatite

Abstract: Early and Late Cretaceous alkaline and alkaline-carbonatitic complexes from southern Brazil are located along the main tectonic lineaments of the South America Platform. Calcium-, magnesium-, and ferrocarbonatites are well represented and frequently associated even in the same complex. Primary carbonates present significant variations in C-O isotopic compositions, which are mainly due to isotope exchange with H2O-CO2-rich hydrothermal fluids, whereas fractional crystallization or liquid immiscibility probably affects the ?18O and ?13C values by no more than 2?‰ Our isotope exchange model implies that the most significant isotopic variations took place in a hydrothermal environment, e.g., in the range 400-80°C, involving fluids with the CO2/H2O ratio ranging from 0.8 to 1. Sr-Nd-Pb isotope systematics highlight heterogeneous mixtures between HIMU and EMI mantle components, similar to the associated alkaline rocks and the flood tholeiites from southern Brazil. In spite of the strong variation shown by C-O isotopes, Sr-Nd-Pb-Os isotopic systematics could be related to an isotopically enriched source where the chemical heterogeneities reflect a depleted mantle "metasomatized" by small-volume melts and fluids rich in incompatible elements. These fluids are expected to have promoted crystallization of K-rich phases in the mantle, which produced a veined network variously enriched in LILE and LREE. The newly formed veins (enriched component) and peridotite matrix (depleted component) underwent a different isotopic evolution with time as reflected by the carbonatites. These conclusions may be extended to the whole Paraná-Etendeka system, where isotopically distinct parent magmas were generated following two main enrichment events of the subcontinental lithospheric mantle at 2.0-1.4 and 1.0-0.5?Ga, respectively, as also supported by Re-Os systematics. The mantle sources preserved the isotopic heterogeneities over a long time, suggesting a nonconvective lithospheric mantle beneath different cratons or intercratonic regions. Overall, the data indicate that the alkaline-carbonatitic magmatism originated from a locally heterogeneous subcontinental mantle.
DS202009-1665
2020
Speich, L., Kohn, S.C.QUIDDIT - a software tool for automated processing of diamond IR spectra.Computers & Geosciences, doi: 10.1016/j.cageo. 2020.104558 available 30p. PdfGlobalQUIDDIT

Abstract: Goal: QUIDDIT (QUantification of Infrared-active Defects in Diamond and Inferred Temperatures) is a novel Python application for fast and automated processing of IR spectra of diamond. It was first developed for the work presented in previous studies (Kohn et al., 2016; Speich et al. 2017 and 2018) and has been used in our lab successfully. The goal of this project is to enhance the software and provide easy access to users in research and industry alike. Read the "Project Log" section for more information.
DS202010-1881
2020
Speich, L., Kohn, S.C.QUIDDIT - Quantification of infrared active defects in diamond and inferred temperatures.Computers and Geosciences, Vol. 144, 7p. PdfGlobalFTIR

Abstract: QUIDDIT is a free Python software-package designed to process Fourier Transform Infrared (FTIR) spectra of diamonds automatically and efficiently. Core capabilities include baseline correction, determination of nitrogen concentration, nitrogen aggregation state and model temperature and fitting of both the 3107 cm-1 and platelet (B’) peaks. These capabilities have allowed the authors to study platelet defects and their relationship to nitrogen aggregation in previous studies. Data visualisation, vital to interpreting and evaluating results, is another key component of the software. QUIDDIT can be applied to single spectra as well as linescan and 2-dimensional map data. Recently, additional features such as manual platelet peak and nitrogen fitting, custom batch peak fitting and two-stage aggregation modelling were made available. QUIDDIT has been used successfully for natural diamonds containing aggregated forms of nitrogen in the past and has since been adapted for the study of diamonds containing C-centres as well.
DS202009-1666
2020
Srivastava, R.K.Early Cretaceous alkaline-alkaline silicate and carbonatite magmatism in the Indian shield - a review: implications for a possible remnant of greater Kerguelen Large Igneous Province.Episodes, Vol. 43, 1, pp. 300-313.Indiacarbonatites

Abstract: The early Cretaceous (ca. 118-100 Ma) alkaline/ultraalkaline silicate and carbonatite magmatism, exclusively recorded in the Chhotanagpur Gneissic Complex and the Shillong Plateau-Mikir Hills in the eastern/northeastern regions of the Indian Shield, have been reviewed to understand their genetic aspects. These are thought to be associated to the Kerguelen hot spot, active in this region during ca. 118-100 Ma. The existing geochemical, geochronological and isotopic data do not support any definite emplacement order for these diverse groups of magmatic suites. It is likely that they were derived from distinct magma batches with direct or indirect involvement of the Kerguelen plume. The available data suggest their possible derivation from the depleted asthenosphere/lithosphere with negligible contribution from the Kerguelen mantle plume. It is likely that mantle plume provided additional heat necessary to melt the asthenosphere/lithosphere. These data also suggest effects of low-pressure crustal contamination, crystal accumulation and fractional crystallization, rather than mantle-derived heterogeneity. These identified magmatic events together with other known magmatic events such as southeastern Tibet, Abor volcanics, SW Australia and eastern Antarctica during ca. 140-100 Ma could be related to the Kerguelen plume and integral part of the Greater Kerguelen Large Igneous Province, and have possible impact on the breakup of East Gondwanaland.
DS202009-1667
2020
Stagno, V., Fei, Y.The redox boundaries of Earth's interiors.Elements, Vol. 16, 3, pp. 167-172.Mantleredox

Abstract: he interior of the Earth is an important reservoir for elements that are chemically bound in minerals, melts, and gases. Analyses of the proportions of redox-sensitive elements in ancient and contemporary natural rocks provide information on the temporal redox evolution of our planet. Natural inclusions trapped in diamonds, xenoliths, and erupted magmas provide unique windows into the redox conditions of the deep Earth, and reveal evidence for heterogeneities in the mantle’s oxidation state. By examining the natural rock record, we assess how redox boundaries in the deep Earth have controlled elemental cycling and what effects these boundaries have had on the temporal and chemical evolution of oxygen fugacity in the Earth’s interior and atmosphere.
DS202004-0534
2020
Stagno, V., Stopponi, V., Kono, Y., D'Arco, A., Lupi, S., Romano, C., Poe, B.T., Foustoukos, D.J., Scarlato, P., Manning, C.E.The viscosity and atomic structure of volatile bearing melililititic melts at high pressure and temperature and the transport of deep carbon.Minerals MDPI, Vol. 10, 267 doi: 10.23390/min10030267 14p. PdfMantleMelililite, carbon

Abstract: Understanding the viscosity of mantle-derived magmas is needed to model their migration mechanisms and ascent rate from the source rock to the surface. High pressure-temperature experimental data are now available on the viscosity of synthetic melts, pure carbonatitic to carbonate-silicate compositions, anhydrous basalts, dacites and rhyolites. However, the viscosity of volatile-bearing melilititic melts, among the most plausible carriers of deep carbon, has not been investigated. In this study, we experimentally determined the viscosity of synthetic liquids with ~31 and ~39 wt% SiO2, 1.60 and 1.42 wt% CO2 and 5.7 and 1 wt% H2O, respectively, at pressures from 1 to 4.7 GPa and temperatures between 1265 and 1755 °C, using the falling-sphere technique combined with in situ X-ray radiography. Our results show viscosities between 0.1044 and 2.1221 Pa•s, with a clear dependence on temperature and SiO2 content. The atomic structure of both melt compositions was also determined at high pressure and temperature, using in situ multi-angle energy-dispersive X-ray diffraction supported by ex situ microFTIR and microRaman spectroscopic measurements. Our results yield evidence that the T-T and T-O (T = Si,Al) interatomic distances of ultrabasic melts are higher than those for basaltic melts known from similar recent studies. Based on our experimental data, melilititic melts are expected to migrate at a rate ~from 2 to 57 km•yr?1 in the present-day or the Archaean mantle, respectively.
DS202004-0535
2020
Stan, C.V., O'Bannon III, E.F., Mukhin, P., Tamura, N., Dobrzhinetskaya, L.X-ray laue microdiffraction and raman spectroscopic investigation of natural silicon and moissanite.Minerals MDPI, Vol. 10, 10030204 12p. PdfGlobalmoissanite

Abstract: Moissanite, SiC, is an uncommon accessory mineral that forms under low oxygen fugacity. Here, we analyze natural SiC from a Miocene tuff-sandstone using synchrotron Laue microdiffraction and Raman spectroscopy, in order to better understand the SiC phases and formation physics. The studied crystals of SiC consist of 4H- and 6H-SiC domains, formed from either, continuous growth or, in one case, intergrown, together with native Si. The native Si is polycrystalline, with a large crystal size relative to the analytical beam dimensions (>1-2 ?m). We find that the intergrown region shows low distortion or dislocation density in SiC, but these features are comparatively high in Si. The distortion/deformation observed in Si may have been caused by a mismatch in the coefficients of thermal expansion of the two materials. Raman spectroscopic measurements are discussed in combination with our Laue microdiffraction results. Our results suggest that these SiC grains likely grew from an igneous melt.
DS202003-0363
2020
Stanley, J.R., Flowers, R.M.Mesozoic denudation history of the lower Orange River and eastward migration of erosion across the southern African plateau.Lithosphere, in press available 14p. PdfAfrica, South Africageochronology

Abstract: Topographic uplift of the southern African Plateau is commonly attributed to mantle causes, but the links between mantle processes, uplift, and erosion patterns are not necessarily straightforward. We acquired apatite (U-Th)/He (AHe) dates from eight kimberlite and basement samples from the lower reaches of the large westward-draining Orange River system with the goal of evaluating the roles of lithospheric modification and river incision on the erosion history here. Average AHe dates range from 79 to 118 Ma and thermal history models suggest that most samples are consistent with a main erosion phase at ca. 120-100 Ma, with some variability across the region indicating a complex erosion history. Major erosion overlaps with the timing of strong lithospheric thermochemical modification as recorded in xenoliths from the studied kimberlites, but the denudation pattern does not mimic the northward progression of lithospheric alteration across the study region. We attribute this area’s denudation history to a combination of mantle effects, rifting, establishment of the Orange River outlet at its current location, and later faulting. When considering these results with other kimberlite-derived surface histories from an ?1000-km-long E-W transect across the plateau, an eastward-younging trend in denudation is evident. The interplay of mantle processes and the shape of the large, west-draining Orange River basin likely control this first order-pattern.
DS202007-1181
2020
Stern, T., Lamb, S., Moore, J.D.P., Okaya, D., Hichmuth, K.High mantle seismic P-wave speeds as a signature for gravitational spreading of superplumes. Science Adavances, Vol. 6, eaba7118 May 27, 9p. PdfAsia, Javageophysics -seismic

Abstract: New passive- and active-source seismic experiments reveal unusually high mantle P-wave speeds that extend beneath the remnants of the world’s largest known large igneous province, making up the 120-million-year-old Ontong-Java-Manihiki-Hikurangi Plateau. Sub-Moho Pn phases of ~8.8 ± 0.2 km/s are resolved with negligible azimuthal seismic anisotropy, but with strong radial anisotropy (~10%), characteristic of aggregates of olivine with an AG crystallographic fabric. These seismic results are the first in situ evidence for this fabric in the upper mantle. We show that its presence can be explained by isotropic horizontal dilation and vertical flattening due to late-stage gravitational collapse and spreading in the top 10 to 20 km of a depleted, mushroom-shaped, superplume head on a horizontal length scale of 1000 km or more. This way, it provides a seismic tool to track plumes long after the thermal effects have ceased.
DS202011-2062
2020
Stolper, E.M., Shortile, O., Antoshechkina, P.M., Asimov, P.D.The effects of solid-solid phase equilibria on the oxygen fugacity of the upper mantle.American Mineralogist, Vol. 105, pp. 1445-1471.Mantleperidotite

Abstract: Decades of study have documented several orders of magnitude variation in the oxygen fugacity (fO2) of terrestrial magmas and of mantle peridotites. This variability has commonly been attributed either to differences in the redox state of multivalent elements (e.g., Fe3+/Fe2+) in mantle sources or to processes acting on melts after segregation from their sources (e.g., crystallization or degassing). We show here that the phase equilibria of plagioclase, spinel, and garnet lherzolites of constant bulk composition (including whole-rock Fe3+/Fe2+) can also lead to systematic variations in fO2 in the shallowest ~100 km of the mantle. Two different thermodynamic models were used to calculate fO2 vs. pressure and temperature for a representative, slightly depleted peridotite of constant composition (including total oxygen). Under subsolidus conditions, increasing pressure in the plagioclase-lherzolite facies from 1 bar up to the disappearance of plagioclase at the lower pressure limit of the spinel-lherzolite facies leads to an fO2 decrease (normalized to a metastable plagioclase-free peridotite of the same composition at the same pressure and temperature) of ~1.25 orders of magnitude. The spinel-lherzolite facies defines a minimum in fO2 and increasing pressure in this facies has little influence on fO2 (normalized to a metastable spinel-free peridotite of the same composition at the same pressure and temperature) up to the appearance of garnet in the stable assemblage. Increasing pressure across the garnet-lherzolite facies leads to increases in fO2 (normalized to a metastable garnet-free peridotite of the same composition at the same pressure and temperature) of ~1 order of magnitude from the low values of the spinel-lherzolite facies. These changes in normalized fO2 reflect primarily the indirect effects of reactions involving aluminous phases in the peridotite that either produce or consume pyroxene with increasing pressure: Reactions that produce pyroxene with increasing pressure (e.g., forsterite + anorthite ? Mg-Tschermak + diopside in plagioclase lherzolite) lead to dilution of Fe3+-bearing components in pyroxene and therefore to decreases in normalized fO2, whereas pyroxene-consuming reactions (e.g., in the garnet stability field) lead initially to enrichment of Fe3+-bearing components in pyroxene and to increases in normalized fO2 (although this is counteracted to some degree by progressive partitioning of Fe3+ from the pyroxene into the garnet with increasing pressure). Thus, the variations in normalized fO2 inferred from thermodynamic modeling of upper mantle peridotite of constant composition are primarily passive consequences of the same phase changes that produce the transitions from plagioclase ? spinel ? garnet lherzolite and the variations in Al content in pyroxenes within each of these facies. Because these variations are largely driven by phase changes among Al-rich phases, they are predicted to diminish with the decrease in bulk Al content that results from melt extraction from peridotite, and this is consistent with our calculations. Observed variations in FMQ-normalized fO2 of primitive mantle-derived basalts and peridotites within and across different tectonic environments probably mostly reflect variations in the chemical compositions (e.g., Fe3+/Fe2+ or bulk O2 content) of their sources (e.g., produced by subduction of oxidizing fluids, sediments, and altered oceanic crust or of reducing organic material; by equilibration with graphite- or diamond-saturated fluids; or by the effects of partial melting). However, we conclude that in nature the predicted effects of pressure- and temperature-dependent phase equilibria on the fO2 of peridotites of constant composition are likely to be superimposed on variations in fO2 that reflect differences in the whole-rock Fe3+/Fe2+ ratios of peridotites and therefore that the effects of phase equilibria should also be considered in efforts to understand observed variations in the oxygen fugacities of magmas and their mantle sources.
DS202001-0042
2019
Sumilova, T., Maximentko, N., Zubov, A., Kovalchuk, N., Ulyashev, V., Kis, V.Varieties of impactites and impact diamonds of the Kara meteorite crater ( Pay-Khoy, Russia).Geoscience Frontiers, 10.1016/j.gsf/2019.09.0111 1p. Abstract Conf.Russia, Siberiaimpact diamonds

Abstract: Impact diamonds are technical material with valuable mechanical properties. Despite of a quite long story from their discovery and huge diamond storages at the Popigai astrobleme (Siberia, Russia) they were not involved into industrial production, first of all because of remoteness of objects, complexity of extraction and economically more favourable synthesis of technical diamonds in the seventies of the past century. However, due to the high hardness of impact diamonds and also to the high demand of new carbon materials, including nanomaterials, the interest towards this type of natural diamonds is significantly increased in the recent years. Although the mentioned Popigai astrobleme is situated in a remote part of Russia it has been studied in more details. At the same time, the less known Kara giant meteorite crater (Pay-Khoy, Russia) is situated essentially closer to the industrial infrastructure of the European part of Russia. This astrobleme, similarly to Popigai, is enriched in impact diamonds as well. But, till recent years it was not deeply studied using modern analytical methods. During our studies in 2015 and 2017 at the territory of the Kara meteorite crater we have distinguished and described 5 varieties of impactites - bulk melt impactites which form cover-like and thick dike bodies; melt ultrahigh-pressure vein bodies and at least 3 types of suevites formed after specific sedimentary target rocks. These varieties have typomorphic features regarding the crystallinity and mineral composition. It was found that all of them have high concentration of microdiamonds formed by high-pressure high temperature pyrolysis mechanism from precursor materials like coal and organic relicts. Using a set of modern mineralogical methods we have found two principal types of diamond morphologies within the Kara impactites - sugar-like after coal diamonds and diamond paramorphs after organic relicts. The Kara diamonds have several accompanying carbon substances including newly formed graphite, glass-like carbon and probably carbyne. The studied diamondiferous Kara impactites provide an essentially novel knowledge of impact processes in sedimentary targets.
DS202012-2252
2020
Sun, C., Dasgupta, R.Thermobarometry of CO2-rich, silica-undersaturated melts constrains cratonic lithosphere thinning through time in areas of kimberlitic magmatism.Earth and Planetary Letters, Vol. 550, 116549, 13p.Global, United States, Wyoming, Canada, Northwest Territories, Europe, Baltic, Indiageothermometry

Abstract: Cratonic lithosphere is believed to have been chemically buoyant and mechanically resistant to destruction over billions of years. Yet the absence of cratonic roots at some Archean terrains casts doubt on the craton stability and longevity on a global scale. As unique mantle-derived melts at ancient continents, silica-poor, kimberlitic melts are ideal tools to constrain the temporal variation of lithosphere thickness and the processes affecting the lithosphere root. However, no reliable thermobarometer exists to date for strongly silica-undersaturated, mantle-derived melts. Here we develop a new thermobarometer for silica-poor, CO2-rich melts using high-temperature, high-pressure experimental data. Our barometer is calibrated based on a new observation of pressure-dependent variation of Al2O3 in partial melts saturated with garnet and olivine, while our thermometer is calibrated based on the well-known olivine-melt Mg-exchange. For applications to natural magmas, we also establish a correction scheme to estimate their primary melt compositions. Applying this liquid-based thermobarometer to the estimated primary melt compositions for a global kimberlite dataset, we show that the equilibration depths between primary kimberlite melts and mantle peridotites indicate a decrease of up to ?150 km in cratonic lithosphere thickness globally during the past ?2 Gyr. Together with the temporal coupling between global kimberlite frequency and cold subduction flux since ?2 Gyr ago, our results imply a causal link between lithosphere thinning and supply of CO2-rich melts enhanced by deep subduction of carbonated oceanic crusts. While hibernating at the lithosphere root, these melts chemically metasomatize and rheologically weaken the rigid lithosphere and consequently facilitate destruction through convective removal in the ambient mantle or thermo-magmatic erosion during mantle plume activities.
DS202004-0536
2020
Sun, J., Rudnick, R.L., Kostrovitsky, S., Kalashnikova, T., Kitajima, K., Li, R., Shu, Q.The origin of low-MgO eclogite xenoliths from Obnazhennaya kimberlite, Siberian craton.Contributions to Mineralogy and Petrology, Vol. 175, 22p. Pdf.Russiadeposit - Obnazhennaya

Abstract: The petrology, mineral major and trace-element concentrations, and garnet oxygen isotopic composition of low-MgO (11-16 wt%) eclogites from the Obnazhennaya kimberlite, Siberian craton, are used to infer their petrogenesis. These eclogites contain two types of compositionally distinct garnet: granular coarse garnet, and garnet exsolution (lamellae and fine-grained garnet) in clinopyroxene. The former record higher temperatures at lower pressures than the latter, which record the last stage of equilibrium at moderate pressure-temperature conditions 2.3-3.7 GPa and 855-1095 °C in the upper mantle at the time of entrainment. Although derived from the garnet stability field, these rocks have low-pressure cumulate protoliths containing plagioclase, olivine, and clinopyroxene as reflected by pronounced positive Eu and Sr anomalies in all eclogites, and low heavy rare earth element (HREE) contents in both minerals and reconstructed bulk rocks for a number of samples. Major elements, transition metals, and the HREE compositions of the reconstructed whole rocks are analogous to modern oceanic gabbro cumulates. Despite geochemical signatures supporting an oceanic crust origin, mantle-like ?18O of the garnets (5.07-5.62‰) for most samples indicates that the protoliths either did not interact with seawater or have coincidently approximately normal igneous values. Some of the eclogite xenoliths have lower SiO2 contents and depleted light REE ((Nd/Yb)N?
DS202008-1450
2020
Sun, J., Rudnick, R.L., Kostrovitsky, S.I., Kalashnikova, T., Kitajima, K., Li, R.P., Shu, Q.The origin of low-MgO eclogite xenoliths from Obnazhennaya kimberlite, Siberia craton.Goldschmidt 2020, 1p. AbstractRussia, Siberiadeposit - Obnazhennaya

Abstract: The petrology, mineral major and trace element concentrations, and garnet oxygen isotopic composition of low-MgO (11-16 wt.%) eclogites from the Obnazhennaya kimberlite, Siberian craton, are used to infer their petrogenesis. These eclogites equilibrated at moderate pressure-temperature conditions 2.3-3.7 GPa and 855- 1095?C at the time of entrainment. Although derived from the garnet stability field, these rocks have low-pressure cumulate protoliths containing plagioclase, olivine, and clinopyroxene as reflected by pronounced positive Eu and Sr anomalies in all eclogites, and low heavy rare earth element (HREE) contents in both minerals and reconstructed bulk rocks for a number of samples. Major elements, transition metals, and the HREE compositions of the reconstructed whole rocks are analogous to modern oceanic gabbro cumulates. Despite geochemical signatures supporting an oceanic crust origin, mantle-like ?18O of the garnets (5.07-5.62 ‰ ) for most samples indicates that the protoliths either did not interact with seawater or have coincidently approximately normal igneous values. Some of the eclogite xenoliths have lower SiO2 contents and depleted light REE ((Nd/Yb)N ? 1) compared to modern oceanic gabbros, suggesting that they experienced partial melting. Positively inclined middle to heavy-REE patterns ((Dy/Yb)N ?1) of the reconstructed bulk rocks mostly result from repeated partial melting in the eclogite stability field, based on melting model calculations. We therefore suggest that the Obnazhennaya low-MgO eclogites may represent the gabbroic section of subducted or foundered basaltic crust that underwent continued partial melting processes at high pressures where garnet was the main residual phase.
DS202001-0043
2019
Sun, T.T., Htay, U.N., Nyunt, T.T., Daw, N.P.Diamond mining at Theindaw, Myanmar.Journal of Gemmology, Vol. 36, pp.594-595.Asia, Myanmardeposit - Theindaw
DS202008-1451
2020
Sun, W-D., Zhang, L-p., Xie, G-z., Hawkesworth. C., Zartmam, R.Carbonatite formed through diamond oxidation.Goldschmidt 2020, 1p. AbstractMantlecarbonatite

Abstract: Carbonatite is a magmatic rock with high carbonate and low silicate contents, which mostly originate in the mantle. It is therefore of critical importance to understand the behavior of carbon in the mantle, and consequently deep carbon recycling. However, the formation of carbonatite is largely unresolved. In particular, the source of carbonatite the carbonate remains obscure. Previous studies showed that the solidus of carbonated mantle peridotite was lower than the Earth’s geotherm in the Archean and the Early Proterozoic era, before ~1.4 Ga ago. Therefore, the mantle should have been severely decarbonated early in Earth’s history. This is consistent with the low carbon abundance in the asthenospheric mantle (~100 ppm), as indicated by low carbonate concentrations in mid-ocean ridge basalts. Consequently, carbonate in young mantle must have been mostly obtained in the post-Archean era by two processes. These are either oxidation of diamond in the mantle or recycling of sedimentary carbonates through plate subduction. Here we show that the Sr and Nd isotope variations in carbonatite may be plausibly explained by mixing of three endmembers, (1) recycled sedimentary carbonates, (2) depleted mantle, and (3) a low Sr and Nd isotopes endmember. The low Sr, Nd carbonate reservoirs for carbonatites of different ages plot roughly on the evolution line of the primitive mantle, suggesting that they were successively released from a well-preserved, non-carbonate mantle source. The preferred candidate for this endmember is carbonate formed through oxidation of diamond by ferric ion released through decomposition of bridgmanite, which is carried up from the lower mantle via background upwelling, compensational to the volume of oceanic slabs penetrating into the lower mantle1.
DS202003-0364
2019
Sun, Z., Palke, A. C., Muyal, J., DeGhionno, D., McClaure, S.F.Geographic origin determination of alexandrite.Gems & Gemology, Vol. 55, 4, pp. 660-681.Russia, South America, Brazil, Africa, Tanzania, Zimbabwe, India, Asia, Sri Lankaalexandrite

Abstract: The gem and jewelry trade has come to place increasing importance on the geographic origin of alexandrite, as it can have a significant impact on value. Alexandrites from Russia and Brazil are usually more highly valued than those from other countries. In 2016, GIA began researching geographic origin of alexandrite with the intent of offering origin determination as a laboratory service. Unfortunately, collecting reliable samples with known provenance can be very difficult. Alexandrite is often recovered as a byproduct of mining for other gemstones (e.g., emerald and corundum), so it can be difficult to secure reliable parcels of samples because production is typically erratic and unpredictable. The reference materials studied here were examined thoroughly for their trace element chemistry profiles, characteristic color-change ranges under daylight-equivalent and incandescent illumination, and inclusion scenes. The data obtained so far allow us to accurately determine geographic origin for alexandrites from Russia, Brazil, Sri Lanka, Tanzania, and India. Future work may help to differentiate alexandrites from other localities.
DS202004-0537
2020
Tamarova, A.P., Marchenko, E.I., Bobrov, A.V., Eremin, N.N., Zinovera, N.G., Irifune, T., Hirata, T., Makino, Y.Interphase REE partitioning at the boundary between the Earth's transition zone and lower mantle: evidence from experiments and atomistic modeling.Minerals MDPI, Vol. 10, 10030262 14p. PdfMantleREE

Abstract: Trace elements play a significant role in interpretation of different processes in the deep Earth. However, the systematics of interphase rare-earth element (REE) partitioning under the conditions of the uppermost lower mantle are poorly understood. We performed high-pressure experiments to study the phase relations in key solid-phase reactions CaMgSi2O6 = CaSiO3-perovskite + MgSiO3-bridgmanite and (Mg,Fe)2SiO4-ringwoodite = (Mg,Fe)SiO3-bridgmanite + (Mg,Fe)O with addition of 1 wt % of REE oxides. Atomistic modeling was used to obtain more accurate quantitative estimates of the interphase REE partitioning and displayed the ideal model for the high-pressure minerals. HREE (Er, Tm, Yb, and Lu) are mostly accumulated in bridgmanite, while LREE are predominantly redistributed into CaSiO3. On the basis of the results of experiments and atomistic modeling, REE in bridgmanite are clearly divided into two groups (from La to Gd and from Gd to Lu). Interphase REE partition coefficients in solid-state reactions were calculated at 21.5 and 24 GPa for the first time. The new data are applicable for interpretation of the trace-element composition of the lower mantle inclusions in natural diamonds from kimberlite; the experimentally determined effect of pressure on the interphase (bridgmanite/CaSiO3-perovskite) REE partition coefficients can be a potential qualitative geobarometer for mineral inclusions in super-deep diamonds.
DS202007-1182
2020
Tanaka, R., Sakamaki, T., Ohtani, E., Fukui, H., Kamada, S., Suzuki, A., Tsutsui, S., Uchiyama, H., Baron, A.Q.R.The sound velocity of wustite at high pressures: implications for low-velocity anomalies at the base of the lower mantle.Progress in Earth and Planetary Science, Vol. 7, 23, 7p. PdfMantlewustite

Abstract: The longitudinal sound velocity (VP) and the density (?) of wüstite, FeO, were measured at pressures of up to 112.3?GPa and temperatures of up to 1700?K using both inelastic X-ray scattering and X-ray diffraction combined with a laser-heated diamond-anvil cell. The linear relationship between VP and ?, Birch’s law, for wüstite can be expressed as VP = 1.55 (1) × ? [g/cm3] ? 2.03 (8) [km/s] at 300?K and VP = 1.61 (1) × ? [kg/m3] ? 2.82 (10) [km/s] at 1700?K. The sound velocity of wüstite is significantly lower than that of bridgmanite and ferropericlase under lower mantle conditions. In other words, the existence of wüstite in the lower mantle can efficiently decrease the seismic velocity. Considering its slow velocity and several mechanisms for the formation of FeO-rich regions at the core-mantle boundary, we confirm earlier suggestions indicating that wüstite enrichment at the bottom of the Earth’s mantle may contribute to the formation of denser ultra-low velocity zones.
DS202001-0044
2019
Tang, F., Taylor, R.J.M., Einsle, J.F., Borlina, C.S., Fu, R.R., Weiss, B.P., Williams, H.M., Williams, W., Nagy, L., Midgley, P.A., Lima, E.A., Bell, E.A., Harrison, T.M., Alexander, E.W., Harrison, R.J.Secondary magnetite in ancient zircon precludes analysis of a Hadean geodynamo. Jack HillsProceedings National Academy of Science, Vol. 116, pp. 407-412.Australiapaleomagnetism

Abstract: Zircon crystals from the Jack Hills, Western Australia, are one of the few surviving mineralogical records of Earth’s first 500 million years and have been proposed to contain a paleomagnetic record of the Hadean geodynamo. A prerequisite for the preservation of Hadean magnetization is the presence of primary magnetic inclusions within pristine igneous zircon. To date no images of the magnetic recorders within ancient zircon have been presented. Here we use high-resolution transmission electron microscopy to demonstrate that all observed inclusions are secondary features formed via two distinct mechanisms. Magnetite is produced via a pipe-diffusion mechanism whereby iron diffuses into radiation-damaged zircon along the cores of dislocations and is precipitated inside nanopores and also during low-temperature recrystallization of radiation-damaged zircon in the presence of an aqueous fluid. Although these magnetites can be recognized as secondary using transmission electron microscopy, they otherwise occur in regions that are indistinguishable from pristine igneous zircon and carry remanent magnetization that postdates the crystallization age by at least several hundred million years. Without microscopic evidence ruling out secondary magnetite, the paleomagnetic case for a Hadean-Eoarchean geodynamo cannot yet been made.
DS202006-0951
2020
Tang, M., Lee, C-T.A., Rudnick, R.L., Condie, K.C.Rapid mantle convection drove massive crustal thickening in the late Archean.Geochimica et Cosmochimica Acta, Vol. 278, pp. 6-15.Mantlecraton

Abstract: The lithospheric mantle beneath Archean cratons is conspicuously refractory and thick compared to younger continental lithosphere ( Jordan, 1988 , Boyd, 1989 ; Lee and Chin, 2014), but how such thick lithospheres formed is unclear. Using a large global geochemical database of Archean igneous crustal rocks overlying these thick cratonic roots, we show from Gd/Yb- and MnO/FeOT-SiO2 trends that crustal differentiation required continuous garnet fractionation. Today, these signatures are only found where crust is anomalously thick (60-70?km), as in the Northern and Central Andes and Southern Tibet. The widespread garnet signature in Archean igneous suites suggests that thickening occurred not only in the lithospheric mantle but also in the crust during continent formation in the late Archean. Building thick crust requires tectonic thickening or magmatic inflation rates that can compete against gravitational collapse through lower crustal flow, which would have been enhanced in the Archean when geotherms were hotter and crustal rocks weaker. We propose that Archean crust and mantle lithosphere formed by thickening over mantle downwelling sites with minimum strain rates on the order of 10?13-10?12 s?1, requiring mantle flow rates associated with late Archean crust formation to be 10-100 times faster than today.
DS202003-0365
2019
Tang, S., Liu, H., Yan, S., Xu, X., Wu, W., Fan, J., Liu, J., Hu, C., Tu, L.A high sensitivity MEMS gravimeter with a large dynamic range. ( not specific to diamonds)Nature.com Microsystems & Nanoengineering, Vol. 5, doi:org/10.1038/ s41378-019-0089-7Globalgeophysics - gravity

Abstract: Precise measurement of variations in the local gravitational acceleration is valuable for natural hazard forecasting, prospecting, and geophysical studies. Common issues of the present gravimetry technologies include their high cost, high mass, and large volume, which can potentially be solved by micro-electromechanical-system (MEMS) technology. However, the reported MEMS gravimeter does not have a high sensitivity and a large dynamic range comparable with those of the present commercial gravimeters, lowering its practicability and ruling out worldwide deployment. In this paper, we introduce a more practical MEMS gravimeter that has a higher sensitivity of 8??Gal/?Hz and a larger dynamic range of 8000 mGal by using an advanced suspension design and a customized optical displacement transducer. The proposed MEMS gravimeter has performed the co-site earth tides measurement with a commercial superconducting gravimeter GWR iGrav with the results showing a correlation coefficient of 0.91.
DS202009-1668
2020
Tappe, S., Budde, G., Stracke, A., Wilson, A., Kleine, T.The tungsten-182 record of kimberlites above the African superplume: exploring links to the core-mantle boundary. Ultradeep diamondsEarth and Planetary Science Letters, Vol. 547, 14p. PdfAfricaLLSVP, superplume

Abstract: Many volcanic hotspots are connected via ‘plume’ conduits to thermochemical structures with anomalously low seismic velocities at the core-mantle boundary. Basaltic lavas from some of these hotspots show anomalous daughter isotope abundances for the short-lived 129I-129Xe, 146Sm-142Nd, and 182Hf-182W radioactive decay systems, suggesting that their lower mantle sources contain material that dates back to Earth-forming events during the first 100 million years in solar system history. Survival of such ‘primordial’ remnants in Earth's mantle places important constraints on the evolution and inner workings of terrestrial planets. Here we report high-precision 182W/184W measurements for a large suite of kimberlite volcanic rocks from across the African tectonic plate, which for the past 250 million years has drifted over the most prominent thermochemical seismic anomaly at the core-mantle boundary. This so-called African LLSVP, or ‘large low shear-wave velocity province’, is widely suspected to store early Earth remnants and is implicated as the ultimate source of global Phanerozoic kimberlite magmatism. Our results show, however, that kimberlites from above the African LLSVP, including localities with lower mantle diamonds such as Letseng and Karowe Orapa A/K6, lack anomalous 182W signatures, with an average W value of 0.0 ± 4.1 (2SD) for the 18 occurrences studied. If kimberlites are indeed sourced from the African LLSVP or superplume, then the extensive 182W evidence suggests that primordial or core-equilibrated mantle materials, which may contribute resolvable W excesses or deficits, are only minor or locally concentrated components in the lowermost mantle, for example in the much smaller ‘ultra-low velocity zones’ or ULVZs. However, the lack of anomalous 182W may simply suggest that low-volume kimberlite magmas are not derived from hot lower mantle plumes. In this alternative scenario, kimberlite magmas originate from volatile-fluxed ambient convecting upper mantle domains beneath relatively thick and cold lithosphere from where previously ‘stranded’ lower mantle and transition zone diamonds can be plucked.
DS202009-1669
2020
Tappe, S., Stracke, A., van Acken, D., Strauss, H., Luguet, A.Origins of kimberlites and carbonatites during continental collision - insights beyond decoupled Nd-Hf isotopes. Earth-Science Reviews, in press available 72p.Global, Africa, South Africadeposit - Cullinan

Abstract: During the past two decades significant progress has been made in understanding the origin and evolution of kimberlites, including relationships to other diamondiferous magma types such as lamproites and aillikites. However, the association of kimberlites and carbonatites on continental shields remains poorly understood, and two opposing ideas dominate the debate. While one school of thought argues that primary carbonatite melts transform into hybrid carbonated silicate magmas akin to kimberlites by assimilation of cratonic mantle material, others use geochemical evidence to show that carbonatite magmas can evolve from near-primary kimberlite melts within the cratonic lithosphere. The 1.15 Ga Premier kimberlite pipe on the Kaapvaal craton in South Africa hosts several kimberlite and carbonatite dykes. Reconstructions of magma compositions suggest that up to 20 wt.% CO2 was lost from near-primary kimberlite melts during ascent through the cratonic lithosphere, but the carbonatite dyke compositions cannot be linked to the kimberlite melts via differentiation. Geochemical evidence, including mantle-like ?13C compositions, suggests that the co-occurring kimberlite and carbonatite dykes represent two discrete CO2-rich magma batches derived from a mixed source in the convecting upper mantle. The carbonatites probed a slightly more depleted source component in terms of Sr-Nd-Hf isotopic compositions relative to the peridotitic matrix that was more effectively tapped by the kimberlites (87Sr/86Sri = 0.70257 to 0.70316 for carbonatites vs. 0.70285 to 0.70546 for kimberlites; ?Ndi = +3.0 to +3.9 vs. +2.2 to +2.8; ?Hfi = -2.2 to +0.7 vs. -5.1 to -1.9). Platinum-group element systematics suggest that assimilation of refractory lithospheric mantle material by the carbonatite melts was negligible (<1 vol.%), whereas between 5 - 35 vol.% of digested cratonic peridotite account for the kimberlite compositions, including the low 187Os/188Os signature (?Osi = -12.7 to -4.5). The kimberlite and carbonatite dykes show similarly strong Nd-Hf isotope decoupling (??Hfi = -10.7 to -7.6 vs. -8.8 to -6.1), regardless of the variable lithospheric mantle imprints. This observation suggests a common sublithospheric origin of the negative ??Hf signature, possibly linked to ancient recycled oceanic crust components in the convecting upper mantle to transition zone sources of CO2-rich magmatism. Mesoproterozoic kimberlite and carbonatite magmatism at Premier was coeval with subduction and collision events along the southern Kaapvaal craton margin during the 1,220 -1,090 Ma Namaqua-Natal orogeny associated with Rodinia supercontinent formation. Thermochronology suggests that the entire Kaapvaal craton was affected by this collisional tectonic event, and it appears that the changing lithospheric stress-field created pathways for deep-sourced kimberlite and carbonatite magmas to reach Earth’s surface. We find that collision-induced (e.g., Premier) and continental breakup-related (e.g., Kimberley) kimberlite magmas are compositionally indistinguishable, with the inference that plate tectonic processes aid solely in the creation of magma ascent pathways without a major influence on deep mantle melting beneath cratons. It follows that on-craton kimberlite magmatism in the hinterland of collision zones is not necessarily more likely to entrain large sublithospheric diamonds than kimberlite eruptions linked to continental breakup. This implies that Premier’s world-class endowment with ‘ultradeep’ Type-II diamonds is not causally related to its setting behind an active orogenic front.
DS202004-0538
2020
Taylor, R.N., Favila-Harris, P., Branney, M.J., Farley, E.M.R., Gernon, T.M., Palmer, M.R.Dynamics of chemically pulsing mantle plume.Earth and Planetary Science Letters, Vol. 537, 116182 14p. PdfMantlehotspot

Abstract: Upwelling plumes from the deep mantle have an impact on the Earth's surface for tens to hundreds of millions of years. During the lifetime of a mantle plume, periodic fluctuations in its composition and temperature have the potential to generate changes in the nature and volume of surface volcanism. We constrain the spatial and temporal scale of compositional changes in a plume using high-resolution Pb isotopes, which identify chemical pulses emerging from the Canary Islands hotspot over the last ?15 million years (Myr). Surface volcanism spanning ? 400 km along the island chain changes composition systematically and synchronously, representing a replenishment of the plume head by a distinct mantle flavour on timescales of 3-5 Myr. These low-frequency compositional changes are also recorded by individual volcanoes, and comprise a sequence of closely-spaced isotopic trajectories. Each trajectory is maintained for ?1 Myr and is preceded and followed by ?0.3 Myr transitions to magmas with distinct isotope ratios. Relatively sharp transitions between periods of sustained isotopic stability require discrete yet coherent heterogeneities rising at speeds of ?100-200 km Myr?1 and extending for ?150 km vertically in the conduit. The long-term synchronous changes require larger scale isotopic domains extending ?600 km vertically through in the plume stem. These observations demonstrate that plumes can chemically “pulse” over short and long-timescales reflecting the characteristics and recycling history of the deep mantle.
DS202005-0763
2020
Teixeira, W., Cordani, U.G., Faleiros, F.M., Sato, K., Maurer, V.C., Ruiz, A.S., Azevedo, E.J.P.The Rio Apa Terrane reviewed: U-Pb zircon geochronology and provenance studies provide paleotectonic links with a growing Proterozoic Amazonia.Earth Science Reviews, Vol. 202, 103089 35p. PdfSouth America, Brazilcraton

Abstract: New and compiled data of zircon U-Pb ages and geochemical-isotopic constraints provide new insights into the orogenic evolution of the Rio Apa Terrane (RAT) and its close affinity with the Amazonia throughout the Proterozoic. Two terranes with distinct evolutionary histories built the RAT. The Porto Murtinho (2070-1940 Ma) and Amoguijá (1870-1820 Ma) magmatic arcs generated the Western Terrane which is mainly composed of short-lived crustal components. Granitoid rocks (1870 Ma) in the distal Corumbá Window indicate that the RAT is much larger in extent. The Caracol accretionary arc (1800-1740 Ma) and the associated Alto Tererê back-arc basin formed away from the Amoguijá belt, being roughly coeval with the adjoining Baía das Garças suite (1776 Ma) and Paso Bravo granitoid rocks (1774-1752 Ma). These tectonic units constitute the Eastern Terrane, whilst the NdHf isotopic constraints indicate derivation from a predominantly juvenile magma source with the minor input of crustal-derived contaminants. The youngest detrital zircon grains from the Alto Tererê samples gave 1740-1790 Ma ages and unimodal age spectra were mainly present. The basin infill was, therefore, most likely concomitant with the exhumation of the Caracol belt. Alto Tererê provenance study also included detritus from passive to active margin settings. The RAT underwent regional cooling between 1.35 and 1.27 Ga, documented mainly by 40Ar39Ar and KAr ages. This age pattern matches a collisional episode that formed the accretionary margin of Amazonia, suggesting that the RAT was a close neighbor at Ectasian times. The geodynamic interplay between them lasted until 1.1 Ga ago, highlighted by some shared-components of a LIP event.
DS202004-0539
2020
Tetley, M.G., Li, Z-X., Matthews, K.J., Williams, S.E.Decoding Earth's plate tectonic history using sparse geochemical data. RodiniaGeoscience Frontiers, in press available 12p. PdfMantleplate tectonics

Abstract: Accurately mapping plate boundary types and locations through time is essential for understanding the evolution of the plate-mantle system and the exchange of material between the solid Earth and surface environments. However, the complexity of the Earth system and the cryptic nature of the geological record make it difficult to discriminate tectonic environments through deep time. Here we present a new method for identifying tectonic paleo-environments on Earth through a data mining approach using global geochemical data. We first fingerprint a variety of present-day tectonic environments utilising up to 136 geochemical data attributes in any available combination. A total of 38301 geochemical analyses from basalts aged from 5-0 Ma together with a well-established plate reconstruction model are used to construct a suite of discriminatory models for the first order tectonic environments of subduction and mid-ocean ridge as distinct from intraplate hotspot oceanic environments, identifying 41, 35, and 39 key discriminatory geochemical attributes, respectively. After training and validation, our model is applied to a global geochemical database of 1547 basalt samples of unknown tectonic origin aged between 1000-410 Ma, a relatively ill-constrained period of Earth's evolution following the breakup of the Rodinia supercontinent, producing 56 unique global tectonic environment predictions throughout the Neoproterozoic and Early Paleozoic. Predictions are used to discriminate between three alternative published Rodinia configuration models, identifying the model demonstrating the closest spatio-temporal consistency with the basalt record, and emphasizing the importance of integrating geochemical data into plate reconstructions. Our approach offers an extensible framework for constructing full-plate, deep-time reconstructions capable of assimilating a broad range of geochemical and geological observations, enabling next generation Earth system models.
DS202005-0764
2019
Tetley, M.G., Williams, S.E., Gurnis, M., Flament, N., Muller, R.D.Constraining absolute plate motions since the Triassic.Journal of Geophysical Research Solid Earth, 10.1029/2019JB0 17442 28p. PdfGlobalgeodynamics

Abstract: The absolute motion of tectonic plates since Pangea can be derived from observations of hotspot trails, paleomagnetism, or seismic tomography. However, fitting observations is typically carried out in isolation without consideration for the fit to unused data or whether the resulting plate motions are geodynamically plausible. Through the joint evaluation of global hotspot track observations (for times <80 Ma), first?order estimates of net lithospheric rotation (NLR), and parameter estimation for paleo-trench migration (TM), we present a suite of geodynamically consistent, data?optimized global absolute reference frames from 220 Ma to the present. Each absolute plate motion (APM) model was evaluated against six published APM models, together incorporating the full range of primary data constraints. Model performance for published and new models was quantified through a standard statistical analyses using three key diagnostic global metrics: root?mean square plate velocities, NLR characteristics, and TM behavior. Additionally, models were assessed for consistency with published global paleomagnetic data and for ages <80 Ma for predicted relative hotspot motion, track geometry, and time dependence. Optimized APM models demonstrated significantly improved global fit with geological and geophysical observations while performing consistently with geodynamic constraints. Critically, APM models derived by limiting average rates of NLR to ~0.05°/Myr and absolute TM velocities to ~27?mm/year fit geological observations including hotspot tracks. This suggests that this range of NLR and TM estimates may be appropriate for Earth over the last 220 Myr, providing a key step toward the practical integration of numerical geodynamics into plate tectonic reconstructions.
DS202009-1670
2020
Tewari, H.C., Kumar, P.Lithospheric framework of the Indian sub-continent through seismic and seismological studies.Episodes, Vol. 43, 1, pp. 622-637.Indiageophysics, seismic

Abstract: Knowledge of the crust and lithospheric structure of the Indian sub-continent primarily comes from several active and passive seismic experiments. These studies are i) controlled source, ii) surface wave studies, iii) receiver functions and v) tomographic studies. The results from these studies in the Indian shield have emanated several interesting features that were hitherto unknown. The peninsular, central and north-western part of the shields, Himalayan and Andaman-Nicobar regions have shown that continental collision and extension from the Proterozoic to Recent time has played an important role in formation and geodynamics of these features. The granulites, in the southern granulite terrain, are formed primarily due to the release of the carbonic fluids from the supracrustal rocks of the subduction zone and volcanic arc environment. These were later exhumed from the deep crust during the collision process. In the central Indian shield the Narmada-Son lineament and the central Indian suture are the main features of the crust. In the Narmada region, mafic intrusion in the upper crust appears to have played an important role in shaping the present structural trends. The Central Indian suture is a collision zone developed due to the interaction of the Bastar and Bundelkhand cratons. In the northwesternpart of the India, the Aravalli-Delhi trend is the controlling feature for the tectonics of the region. Demarcation of the various boundaries between different crustal units are marked across the trend, by changes in the dip direction and steeply dipping reflections, cutting across the nearly horizontal reflections at various depths in the crust. Plate tectonics appears to be responsible for generation of this belt. In the crustal block between the Delhi-Aravalli system and the Narmada-Son Lineament, which is running to the south of the Saurashtra peninsula the crust up uplifted by as much as 4 to 6 km as compared to the regions outside these trends. Apart from the deep crustal structure, lithospheric and upper mantle studies till 660km depth have also been conducted in the entire Indian plate using seismological tools e.g. P-to-s and S-to-p receiver function, surface waves dispersion and tomographic studies. The Himalayan region shows the architecture of the under thrusting Indian plate beneath the Tibetan plate in the north and north-west, while the subduction beneath the Burmese arc has been mapped in the eastern part. Further, a number of studies have been conducted in the Andaman-Nicobar Islands to image the subduction of Indian oceanic plate in order to understand the genesis of earthquakes in these regions.
DS202006-0952
2020
Thomas, R., Davidson, P., Rericha, A.Emerald from the Habachtal: new observations.Mineralogy and Petrology, Vol. 114, pp. 161-173.Europe, Austriaemerald

Abstract: The emerald mineralization in the Habachtal (Austria) is geologically and tectonically complex, and previous investigators have identified fluid inclusion evidence for a hydrothermal/metamorphic origin for the emeralds. In this paper we report the discovery of emeralds with a distinctly different inclusion population including melt inclusions, which demonstrates that at least some and probably most of the emerald mineralization in the Habachtal occurred from an extremely fluid-rich pegmatite-like aluminosilicate melt under supercritical conditions, at high temperatures and moderate pressures (~700 °C, 5 kbar). This conclusion is based on the presence of very highly-ordered graphite, and extremely water-rich melt inclusions in emerald. The Lorentz distribution of MgCO3 against the water concentration is a very robust proof for the supercritical state. We suggest that the purely metamorphic model, based on the extrapolation of fluid inclusion data to the regional metamorphic conditions (550 °C and 5 kbar) by some previous investigators are inconsistent with our finding of high-temperature indications (well-ordered graphite, high-temperature fluid inclusions and melt inclusions). This apparent conflict suggests a more complex situation and requires a re-investigation of the emerald genesis in the Habachtal deposit.
DS202005-0765
2020
Thompson, A.Diversity and inclusion: Do we know our subconscious biases? (good refs) View of factors and survey continued from overview in No. 120 SEG.SEG Discovery ( former NewsLetter), No. 121, April p. 15 Globalgeoscience
DS202005-0766
2020
Thompson, H.Here's how the periodic table gets new elements.. From discovery to confirmation and naming the path is rarely simple. ( last time was 4 elements in 2016.Science News, videoGlobalperiodic table
DS202011-2063
2020
Thurston, M., Young, N., Gordon-Coker, C.Farewell to Wynand Kleingeld.Mathematical Geosciences, Vol. 52, pp. 971-973.GlobalKleingeld
DS202012-2253
2020
Tian, D., Lv, M., Wei, S.S., Dorfman, S.M., Shearer, P.M.Global variations of Earth's 520- and 550-km discontinuities.Earth and Planetary Letters, Vol. 552, 116600, 13p. PdfMantlecore-mantle boundary

Abstract: We investigate seismic discontinuities in the mantle transition zone (MTZ) by analyzing SS precursors recorded at global seismic stations. Our observations confirm the global existence of the 520-km discontinuity. Although substantial regional depth variations in the 520-km discontinuity are generally correlated with temperature in the mid-MTZ, they cannot be fully explained by the Clapeyron slope of the wadsleyite-ringwoodite phase transition, suggesting both thermal and compositional heterogeneities in the MTZ. A second discontinuity at ?560-km depth, previously interpreted as splitting of the 520-km discontinuity, is most commonly detected in cold subduction zones and hot mantle regions. The depth separation between the 520- and 560-km discontinuities varies from ?80 km in cold regions to ?40 km in hot areas. The exsolution of calcium-perovskite (Ca-pv) from majorite garnet has been proposed to explain the velocity and density changes across the 560-km discontinuity. However, the gradual exsolution of perovskite and partitioning of Ca and Al between perovskite and garnet appear inconsistent with the relatively “sharp” discontinuity in seismic observations and thus need to be revisited in the future. Nevertheless, because the only known transition in major minerals at this depth in the MTZ is the formation of Ca-pv, the existence of the 560-km discontinuity may imply localized high calcium concentrations in the mid-MTZ possibly related to the recycling of oceanic crust.
DS202011-2064
2020
Tian, G., Liu, J., Scott, J.M., Chen, L-H., Pearson, D.G., Chu, Z.Architecture and evolution of the lithospheric roots beneath circum-cratonic orogenic belts - the Xing'an Mongolian orogenic belt and its relationship with adjacent North China and Siberian cratonic roots.Lithos, Vol. 376-377, 18p. PdfChina, Russia, Siberiaxenoliths

Abstract: The accretionary mobile belts surrounding ancient cratonic cores are an important facet of the growth and preservation of continental landmasses. Peridotites from Nuominhe in the Xing'an Mongolia Orogenic Belt (XMOB) provide an additional opportunity to examine the age, structure and evolution of mantle lithosphere separating two of the largest existing ancient continental nuclei: the North China Craton and the Siberian Craton. This suite of mantle rocks comprises fertile to refractory garnet- and spinel-facies harzburgites and lherzolites. Their lithophile element systematics show that the peridotites were metasomatized to variable extent by silicate?carbonate melts. Despite this, the highly siderophile element and Os isotope systematics appear to have been largely undisturbed. The Nuominhe peridotites have Re-depletion Os model ages (TRD) that range from 0.5 Ga to 2.4 Ga, with three peaks/major ranges at ~2.0-2.4 Ga, ~1.4-1.5 Ga and ~ 0.8 Ga, of which the latter two are closely similar to those data from other XMOB localities reported in the literature. The only section of the mantle that appears to have ages which correlate with crust formation is the suite with Neoproterozoic (~0.8 Ga) depletion ages, while the older mantle domains document older episodes of mantle depletion. Given the lack of correlation between equilibrium temperatures and bulk composition or TRD ages, the Nuominhe peridotites were inter-mixed in the mantle column, most likely as a result of incorporation of recycled older continental mantle fragments into juvenile Neoproterozoic mantle during the orogenic processes responsible for new lithosphere formation. Geothermobarometry of the Nuominhe peridotites indicates a conductive geotherm of ~60 mWm?2 and therefore a lithosphere thickness of ~125 km, which is thicker than most Phanerozoic continental terranes, and even thicker than Proterozoic regions that comprise the larger cratonic unit of the Siberian craton. This thick Proterozoic lithosphere sandwiched between the converging North China and Siberian cratons was evidently partly constructed from recycled refractory continental mantle fragments, perhaps extant in the convecting mantle, or in-part derived from the surrounding cratons, leading to a composite nature of the mantle in this re-healed continental suture. Re-accretion of recycled refractory old continental mantle fragments plays a significant role in affecting mantle composition and controlling the thickness of circum-cratonic landmasses between cratonic blocks.
DS202009-1671
2020
Tiira, T., Janik, T., Skrzynik, T., Komminaho, K., Heinonen, A., Veikkolainen, T., Vakeva, S., Korja, A.Full scale crustal interpretation of Kokkola-Kymi ( KOKKY) seismic profile, Fennoscandian shield.Pure and Applied Geophysics, Vol. 177, 8, pp. 3775-3795. pdfEurope, Finlandgeophysics - seismics

Abstract: The Kokkola-Kymi Deep Seismic Sounding profile crosses the Fennoscandian Shield in northwest-southeast (NW-SE) direction from Bothnian belt to Wiborg rapakivi batholith through Central Finland granitoid complex (CFGC). The 490-km refraction seismic line is perpendicular to the orogenic strike in Central Finland and entirely based on data from quarry blasts and road construction sites in years 2012 and 2013. The campaign resulted in 63 usable seismic record sections. The average perpendicular distance between these and the profile was 14 km. Tomographic velocity models were computed with JIVE3D program. The velocity fields of the tomographic models were used as starting points in the ray tracing modelling. Based on collected seismic sections a layer-cake model was prepared with the ray tracing package SEIS83. Along the profile, upper crust has an average thickness of 22 km average, and P-wave velocities (Vp) of 5.9-6.2 km/s near the surface, increasing downward to 6.25-6.40 km/s. The thickness of middle crust is 14 km below CFGC, 20 km in SE and 25 km in NW, but Vp ranges from 6.6 to 6.9 km/s in all parts. Lower crust has Vp values of 7.35-7.4 km/s and lithospheric mantle 8.2-8.25 km/s. Moho depth is 54 km in NW part, 63 km in the middle and 43 km in SW, yet a 55-km long section in the middle does not reveal an obvious Moho reflection. S-wave velocities vary from 3.4 km/s near the surface to 4.85 km/s in upper mantle, consistently with P-wave velocity variations. Results confirm the previously assumed high-velocity lower crust and depression of Moho in central Finland.
DS202002-0219
2020
Tilhac, R., Oliveira, B., Griffin, W.L., O'Reilly, S.Y., Schaefer, B.F., Alard, O., Ceuleneer, G., Afonso, J.C., Gregoire, M.Reworking of old continental lithosphere: unradiogenic Os and decoupled Hf-Nd isotopes in sub-arc mantle pyroxenites.Lithos, Vol. 354-355, 19p. pdfEurope, Spainpyroxenites

Abstract: Mantle lithologies in orogenic massifs and xenoliths commonly display strikingly different Hf- and Nd-isotope compositions compared to oceanic basalts. While the presence of pyroxenites has long been suggested in the source region of mantle-derived magmas, very few studies have reported their combined HfNd isotope compositions. We here report the first LuHf data along with ReOs data and S concentrations on the Cabo Ortegal Complex, where the pyroxenite-rich Herbeira massif has been interpreted as remnants of a delaminated arc root. The pyroxenites, chromitites and their host harzburgites show a wide range of whole-rock 187Re/188Os and 187Os/188Os (0.16-1.44), indicating that Re was strongly mobilized, partly during hydrous retrograde metamorphism but mostly during supergene alteration that preferentially affected low-Mg#, low Cu/S pyroxenites. Samples that escaped this disturbance yield an isochron age of 838 ± 42 Ma, interpreted as the formation of Cabo Ortegal pyroxenites. Corresponding values of initial 187Os/188Os (0.111-0.117) are relatively unradiogenic, suggesting limited contributions of slab-derived Os to primitive arc melts such as those parental to these pyroxenites. This interpretation is consistent with radiogenic Os in arc lavas being mostly related to crustal assimilation. Paleoproterozoic to Archean Os model ages confirm that Cabo Ortegal pyroxenites record incipient volcanic arc magmatism on the continental margin of the Western African Craton, as notably documented by zircon UPb ages of 2.1 and 2.7 Ga. LuHf data collected on clinopyroxene and amphibole separates and whole-rock samples are characterized by uncorrelated 176Lu/177Hf and 176Hf/177Hf (0.2822-0.2855), decoupled from Nd-isotope compositions. This decoupling is ascribed to diffusional disequilibrium during melt-peridotite interaction, in good agreement with the results of percolation-diffusion models simulating the interaction of an arc melt with an ancient melt-depleted residue. These models notably show that HfNd isotopic decoupling such as recorded by Cabo Ortegal pyroxenites and peridotites (??Hf(i) up to +97) is enhanced during melt-peridotite interaction by slow diffusional re-equilibration and can be relatively insensitive to chromatographic fractionation. Finally, we discuss the hypothesis that arc-continent interaction may provide preferential conditions for such isotopic decoupling and propose that its ubiquitous recognition in peridotites reflects the recycling of sub-arc mantle domains derived from ancient, reworked SCLM.
DS202003-0366
2020
Tovey, M., Giuliani, A., Phillips, D., Moss, S.Controls on the explosive emplacement of diamondiferous kimberlites: new insights from hypabyssal and pyroclastic units in the Diavik mine, Canada.Lithos, in press available, 55p. PdfCanada, Northwest Territoriesdeposit - Diavik

Abstract: Kimberlites are mantle-derived magmas that either crystallise as hypabyssal intrusions, erupt explosively after rapid ascent to the surface, or less commonly form lava lakes and flows, thereby creating texturally distinct kimberlite units. Efforts to fully understand the processes responsible for the explosive eruption of kimberlite magmas have been hindered by the widespread alteration and crustal contamination of most volcaniclastic kimberlites. To address this issue, we have undertaken a detailed petrographic and mineral chemical study of fresh (i.e. minimally altered) pyroclastic and hypabyssal kimberlites (HK) from the ca. 55-56?Ma A154 North and South kimberlite pipes in the Diavik Mine (Lac de Gras, Canada). These localities host exceptionally fresh kimberlites and are therefore ideally suited to this study. Kimberlite emplacement at A154 North and South initiated with the intrusion of hypabyssal kimberlite (external dykes), and was followed by the explosive formation of kimberlite pipes and volcaniclastic kimberlite infill. Subsequent kimberlite magmas intruded the volcaniclastic kimberlite units forming multiple cross-cutting, internal dykes. The studied volcaniclastic units feature abundant rounded magmaclasts and massive textures, suggestive of primary deposits. These units are classified as pyroclastic kimberlites (PK). Pyroclastic and hypabyssal kimberlite units at Diavik exhibit subtle mineral compositional differences. Samples from both internal HK units and PK units feature identical compositions for liquidus olivine rims (Mg#?=?90.5?±?0.1 and 90.7?±?0.2, respectively), with a marginally lower Mg# of 90.2?±?0.2 in olivine rims from the external HK dykes. Similarly, early-formed chromite compositions are the same for internal HK and PK units (Cr#?=?79.1?±?3.4 and 78.3?±?5.7; Mg#?=?60.0?±?1.3 and 60.0?±?2.2), but, differ in the external HK units (Cr#?=?86.9?±?2.7; Mg#?=?52.8?±?1.9). The internal HK and PK units also exhibit lower carbonate contents than the internal HK units. These compositional differences indicate that the external dykes were probably derived from slightly different primitive melt compositions to those parental to the internal HK and PK units. Spinel evolutionary trends from chromite to magnesian ulv?spinel-magnetite (MUM) compositions (Fe3+#?=?47.2?±?5.8 and 49.7?±?9.3; Cr#?=?25.7?±?11.0 and 17.0?±?14.0 for MUM) are indistinguishable in internal HK and PK samples. These results demonstrate that the primitive melt compositions and early magmatic evolution processes are identical for the internal kimberlite units, regardless of whether the kimberlite melts erupted explosively or were emplaced as shallow intrusions. However, magmaclasts in the PK units contain higher abundances of phlogopite (<52 vol%) and lower quantities of carbonate (<4 vol%) than the groundmass of the hypabyssal kimberlite samples (<2 vol% and 25-65 vol%, respectively). This indicates that the explosively erupted magmas featured higher H2O/CO2 ratios. In contrast, abundant carbonates, including dolomite, in the internal HK samples indicate that CO2, and therefore low H2O/CO2 ratios, were retained during the emplacement of this magma, which likely prevented phlogopite crystallisation. Lower K and Rb whole-rock compositions for internal HK samples compared to PK samples, are attributed to the removal of these components in late-stage kimberlitic fluids, as indicated by hydrothermal alteration of the adjacent volcaniclastic kimberlite units. The above results clearly rule out variations in primitive melt composition and melt evolution trajectories as a primary control on the explosive behaviour of the kimberlite magmas at Diavik. Our study also emphasises how volatile loss resulting from different emplacement styles can have a profound effect on the whole-rock compositions and petrography of kimberlite units. Controls on kimberlite explosivity at Diavik are likely due to external factors, such as local stress regimes, the availability of groundwater (i.e. phreatomagmatism) and differing magma supply rates.
DS202008-1452
2020
Tovey, M., Giuliani, A., Phillips, D., Sarkar, C., Pearson, D.G., Nowicki, T., Carlson, J.Decoupling of kimberlite source and primitive melt compositions.Goldschmidt 2020, 1p. AbstractSouth America, Brazil, Africa, South Africa, Canada, Northwest Territoriesgeochronology

Abstract: Kimberlites emplaced since ~2 Ga show Nd and Hf isotopic compositions that follow a remarkably consistent linear evolution [1]. However, kimberlites emplaced <200 Ma within a few thousand kilometers of the western paleo-margin of Pangea (i.e. Brazil, southern Africa, and Lac de Gras in western Canada) deviate towards more enriched Nd and Hf isotopic compositions possibly due to contribution by recycled crustal material, introduced to the deep kimberlite source via subduction [1]. To address this anomaly further we have compared new and existing geochronological and Nd isotopic data for 28 kimberlites from Lac de Gras (LDG; ca. 47 - 75 Ma) with their olivine and spinel mineral chemistries. Olivine grains typically include mantle-derived xenocrystic cores (Mg# = 83.5-94.2) overgrown by magmatic rims with relatively constant Mg# values. Olivine rims and chromite are the first magmatic phases to crystallise from kimberlite and can be used as proxies for primitive melt compositions. The average Mg# of olivine cores from each kimberlite is positively correlated with average olivine rim Mg#, suggesting that assimilation of heterogeneous lithospheric mantle contributed to the primitive melt compositions. The ?Nd(i) values from whole-rock and perovskite from LDG kimberlites vary between -3.4 and -0.4 that are negatively correlated with their emplacement ages. This correlation is indicative of an evolving kimberlite source which may have resulted from a progressively lower contribution of recycled material. No systematic relationships were observed between olivine rim or chromite compositions and age or Nd isotopic composition. This observation highlights decoupling between kimberlite source evolution and primitive melt compositions due to the combined effects of crustal recycling in the kimberlite source and lithospheric mantle assimilation during kimberlite ascent.
DS202001-0045
2019
Tschauner, O.High pressure minerals.American Mineralogist, Vol. 104, pp. 1701-1731.MantleUHP

Abstract: This article is dedicated to the occurrence, relevance, and structure of minerals whose formation involves high pressure. This includes minerals that occur in the interior of the Earth as well as minerals that are found in shock-metamorphized meteorites and terrestrial impactites. I discuss the chemical and physical reasons that render the definition of high-pressure minerals meaningful, in distinction from minerals that occur under surface-near conditions on Earth or at high temperatures in space or on Earth. Pressure-induced structural transformations in rock-forming minerals define the basic divisions of Earth's mantle in the upper mantle, transition zone, and lower mantle. Moreover, the solubility of minor chemical components in these minerals and the occurrence of accessory phases are influential in mixing and segregating chemical elements in Earth as an evolving planet. Brief descriptions of the currently known high-pressure minerals are presented. Over the past 10 years more high-pressure minerals have been discovered than during the previous 50 years, based on the list of minerals accepted by the IMA. The previously unexpected richness in distinct high-pressure mineral species allows for assessment of differentiation processes in the deep Earth.
DS202005-0767
2020
Tscuchiya, T., Tsuchiya, J., Dekura, H., Ritterbex, S.Ab initio study on the lower mantle minerals.Annual Review of Earth and Planetary Sciences, Vol. 48, 21p. pdfMantlemineralogy

Abstract: Recent progress in theoretical mineral physics based on the ab initio quantum mechanical computation method has been dramatic in conjunction with the rapid advancement of computer technologies. It is now possible to predict stability, elasticity, and transport properties of complex minerals quantitatively with uncertainties that are comparable to or even smaller than those attached in experimental data. These calculations under in situ high-pressure (P) and high-temperature conditions are of particular interest because they allow us to construct a priori mineralogical models of the deep Earth. In this article, we briefly review recent progress in studying high-P phase relations, elasticity, thermal conductivity, and rheological properties of lower mantle minerals including silicates, oxides, and some hydrous phases. Our analyses indicate that the pyrolitic composition can describe Earth's properties quite well in terms of density and P- and S-wave velocity. Computations also suggest some new hydrous compounds that could persist up to the deepest mantle and that the postperovskite phase boundary is the boundary of not only the mineralogy but also the thermal conductivity. 1) The ab initio method is a strong tool to investigate physical properties of minerals under high pressure and high temperature. 2) Calculated thermoelasticity indicates that the pyrolytic composition is representative to the chemistry of Earth's lower mantle. 3) Simulations predict new dense hydrous phases stable in the whole lower mantle pressure and temperature condition. 4) Calculated lattice thermal conductivity suggests a heat flow across the core mantle boundary no greater than 10 TW.
DS202007-1183
2020
Tscuchiya, T., Tsuchiya, J., Dekura, H., Ritterbex, S.Ab initio study on the lower mantle minerals.Annual Review of Earth and Planetary Sciences, Vol. 48, 1, pp. 99-119.Mantlemineralogy

Abstract: Recent progress in theoretical mineral physics based on the ab initio quantummechanical computation method has been dramatic in conjunction with the rapid advancement of computer technologies. It is now possible to predict stability, elasticity, and transport properties of complex minerals quantitatively with uncertainties that are comparable to or even smaller than those attached in experimental data. These calculations under in situ high-pressure (P) and high-temperature conditions are of particular interest because they allow us to construct a priori mineralogical models of the deep Earth. In this article, we briefly review recent progress in studying high-P phase relations, elasticity, thermal conductivity, and rheological properties of lower mantle minerals including silicates, oxides, and some hydrous phases. Our analyses indicate that the pyrolitic composition can describe Earth’s properties quite well in terms of density and P- and S-wave velocity. Computations also suggest some new hydrous compounds that could persist up to the deepestmantle and that the postperovskite phase boundary is the boundary of not only the mineralogy but also the thermal conductivity.
DS202003-0367
2020
Turetsky, M.R., Abbott, B.W., Jones, M.C., Walter Anthony, K.. Olefeldt, D., Schuur, E.A.G., Grosse, G., Kuhry, P., Higelius, G., Koven, C., Lawrence, D.M., Gibson, C., Sannel, A.B.K., McGuire, A.D.Carbon release through abrupt permafrost thaw. ( not specific to diamonds but interest)Nature Geoscience, Vol. 13, pp. 138-143.Mantlecarbon

Abstract: The permafrost zone is expected to be a substantial carbon source to the atmosphere, yet large-scale models currently only simulate gradual changes in seasonally thawed soil. Abrupt thaw will probably occur in <20% of the permafrost zone but could affect half of permafrost carbon through collapsing ground, rapid erosion and landslides. Here, we synthesize the best available information and develop inventory models to simulate abrupt thaw impacts on permafrost carbon balance. Emissions across 2.5?million?km2 of abrupt thaw could provide a similar climate feedback as gradual thaw emissions from the entire 18?million?km2 permafrost region under the warming projection of Representative Concentration Pathway 8.5. While models forecast that gradual thaw may lead to net ecosystem carbon uptake under projections of Representative Concentration Pathway 4.5, abrupt thaw emissions are likely to offset this potential carbon sink. Active hillslope erosional features will occupy 3% of abrupt thaw terrain by 2300 but emit one-third of abrupt thaw carbon losses. Thaw lakes and wetlands are methane hot spots but their carbon release is partially offset by slowly regrowing vegetation. After considering abrupt thaw stabilization, lake drainage and soil carbon uptake by vegetation regrowth, we conclude that models considering only gradual permafrost thaw are substantially underestimating carbon emissions from thawing permafrost.
DS202010-1882
2020
Ugapeva, S., Afanasiev, V., Pavlushin, A., Eliseev, A.Main features of Yakutites from Ebelyakh placer.World Multidisciplinary Earth Sciences Symposium ( researchgate), 7p. PdfRussialonsdaleite

Abstract: Yakutites (polycrystalline diamonds with lonsdaleite admixture) from the Ebelyakh placer (Yakutia, Russia) have been studied by optical microscopy, Raman spectroscopy, and neutron diffraction in order to reveal their difference from tagamite-hosted diamonds of the Popigai impact crater. The yakutite aggregates are 2.0 mm to 13.0 mm in size and have a shapeless morphology or sometimes preserve hexagonal contours of primary graphite. Raman spectra are characterized by a broadened line in the region of cubic 3C diamond, which is interpreted as the sum of spectra from cubic 3C diamond and three peaks related to Lonsdaleite: 1338 (E1g), 1280 (A1g) and 1224 (E2g). On the surface of yakutites revealed the presence of a silicate glass film. The main elements are iron, silicon from the surrounding silicate matter. Neutron stress diffractometry showed the content of diamond and Lonsdaleite in the sample of yakutite by 50%, two cases of preferential orientation of two phases were recorded: (110) diamond // (110) Lonsdaleite; (111) diamond // (001) Lonsdaleite. Both yakutites and tagamite-hosted diamonds are of impact origin and share similarity in the phase composition consisting of more abundant diamond and subordinate amounts of lonsdaleite. Differences between them depend on the place of their formation. Yakutites were formed in the epicenter of the explosion and were thrown out of the crater at a distance of more than 550 km in radial directions, and from the vertical ejection - they got back to the crater. In tagamites, impact diamonds were formed simultaneously with the rock melting due to the shock wave that came from the epicenter. The presence of a silicate glass film on the surface of yakutites indicates that they were hardened after ejection from the crater. Yakutites represent distinct mineral fraction outside the crater. They are found as placers along with common diamonds and other detritus. Within the crater they are genetically related to suevites - tuffaceous component of the impactites and enter the crater placers due to the physical weathering of suevites. Tagamite diamonds practically do not occur in the crater placers, because tagamite is a very hard rock and in the absence of chemical weathering these diamonds can't be released. Thus, diamonds from tagamites and yakutites, having a common impact nature, differ in some properties determined by the place of formation and post-impact history.
DS202011-2065
2020
Vainer, S., Matmon, A., Erel, A.J., Hidy, A.J., Crouvi, O., De Wit, M., Geller, Y.Landscape responses to intraplate deformation in the Kalahari constrained by sediment provenance and chronology in the Okavango Basin.Basin Research, in press available Africa, South Africageomorphology

Abstract: The structural depression that occupies the Okavango Basin in southern Africa comprises a depo?centre within the intracratonic Kalahari Basin where sediments of the Cenozoic Kalahari Group have accumulated. The Okavango Basin has been formed due to stretching and subsidence at an area of diffused deformation, southwestwards to the main East African Rift System (EARS). Sediments from two full Kalahari Group sequences, located on opposite sides of the Gumare Fault that forms a major fault within the Okavango Basin, were studied to determine their provenance and chronology. Terrestrial Cosmogenic Nuclide (TCN) 26Al/10Be burial dating was used to constrain a chronostratigraphical framework, and Pb, Sr, and Nd isotopic ratios combined with geochemical and sedimentological analyses were applied to track the source areas of the sediments.Results indicate the following sequence of basin filling: (a) Accumulation between ca. 4-3 Ma during which the currently downthrown (southern) block received a mixture of sediments mostly from the Choma?Kalomo, Ghanzi?Chobe, and Damara terranes, and possibly from the Lufilian Belt and/or Karoo basalts during earlier stages of deposition. Simultaneously, the upthrown (northern) block received sediments from more distant Archean sources in the Zimbabwe and/or Kasai cratons, (b) Hiatus in sedimentation occurred at both sites between ca. 3-2 Ma, (c) Sediments on both sides of the Gumare Fault share a similar source (Angolan Shield) with minor distinct contributions to the downthrown block from the Kasai Craton and local sources input to the upthrown block, and (d) Regional distribution of aeolian sand since at least 1 Ma. The change in source areas is attributed to rearrangements of the drainage systems that were probably linked to vertical crustal movements on the margins of the Okavango Basin. The tectonically induced morphodynamics controlled the landscape evolution of the endorheic basin where vast lakes, wetlands and salt pans have developed through time.
DS202011-2066
2020
Van Bockstael, S.From boom to bust, and back again: the Tortiya diamond fields of Cote d'Ivoire, 1947-2018.Canadian Journal of Development Studies, Vol. 41, 3, pp. 450-466. pdfAfrica, Ivory Coasthistory

Abstract: Implementation of the African Mining Vision in Côte d’Ivoire is weak, and AMV domestication is unlikely to happen soon. Focusing on the artisanal and small-scale mining (ASM) sector, a key section of the AMV, we look at the tumultuous recent history of the diamond mining town Tortiya. The subject of a halting and uneven formalisation process, the case is emblematic for the lack of interest shown in ASM at a policy level. This is due to high costs, and low political and economic returns of formalisation. It underscores a broader lack of strategic vision for the mining sector.
DS202008-1453
2020
van den Broeck, J.M., Gaina, C.Microcontinents and continental fragments associated with subduction systems.Tectonics, in press available, e2020TC006063 39p. PdfGlobalsubduction

Abstract: Microcontinents and continental fragments are small pieces of continental crust that are surrounded by oceanic lithosphere. Although classically associated with passive margin formation, here we present several preserved microcontinents and continental fragments associated with subduction systems. They are located in the Coral Sea, South China Sea, central Mediterranean and Scotia Sea regions and a ‘proto?microcontinent’, in the Gulf of California. Reviewing the tectonic history of each region and interpreting a variety of geophysical data allows us to identify parameters controlling the formation of microcontinents and continental fragments in subduction settings. All these tectonic blocks experienced long, complex tectonic histories with an important role for developing inherited structures. They tend to form in back?arc locations and separate from their parent continent by oblique or rotational kinematics. The separated continental pieces and associated marginal basins are generally small and formation is quick (<50 Myr). Microcontinents and continental fragments formed close to large continental masses tend to form faster than those created in systems bordered by large oceanic plates. A common triggering mechanism for formation is difficult to identify, but seems to be linked with rapid changes of complex subduction dynamics. The young ages of all contemporary pieces found in situ suggest that microcontinents and continental fragments in these settings are short lived. Although presently the amount of in?situ subduction?related microcontinents is meagre (an area of 0.56% and 0.28% of global, non?cratonic, continental crustal area and crustal volume respectively), through time microcontinents contributed to terrane amalgamation and larger continent formation.
DS202009-1672
2020
van den Broek, J.M., Gaina, C.Microcontinents and continental fragments associated with subduction systems.Tectonics, 10.1029/2020/TC006063 29p. PdfGlobalsubduction

Abstract: Microcontinents and continental fragments are small pieces of continental crust that are surrounded by oceanic lithosphere. Although classically associated with passive margin formation, here we present several preserved microcontinents and continental fragments associated with subduction systems. They are located in the Coral Sea, South China Sea, central Mediterranean and Scotia Sea regions, and a “proto?microcontinent,” in the Gulf of California. Reviewing the tectonic history of each region and interpreting a variety of geophysical data allows us to identify parameters controlling the formation of microcontinents and continental fragments in subduction settings. All these tectonic blocks experienced long, complex tectonic histories with an important role for developing inherited structures. They tend to form in back?arc locations and separate from their parent continent by oblique or rotational kinematics. The separated continental pieces and associated marginal basins are generally small and their formation is quick (<50 Myr). Microcontinents and continental fragments formed close to large continental masses tend to form faster than those created in systems bordered by large oceanic plates. A common triggering mechanism for their formation is difficult to identify, but seems to be linked with rapid changes of complex subduction dynamics. The young ages of all contemporary pieces found in situ suggest that microcontinents and continental fragments in these settings are short lived. Although presently the amount of in?situ subduction?related microcontinents is meager (an area of 0.56% and 0.28% of global, non?cratonic, continental crustal area and crustal volume, respectively), through time microcontinents contributed to terrane amalgamation and larger continent formation.
DS202006-0953
2020
Van Rytheoven, A.D., Schulze, D.J., Davis, D.W.Ultramafic xenoliths from the 1.15 Ga Certac kimberlite, eastern Superior craton.The Canadian Mineralogist, Vol. 56, pp. 267-286. pdfCanada, Quebecdeposit - Certac

Abstract: Xenoliths and xenocrysts of mantle material from kimberlite dikes located underground at the Certac Au mine, Québec, in the eastern Superior Craton, were studied in terms of the major element composition of their constituent minerals. The kimberlite was dated at 1151 ± 46 Ma by the U-Pb perovskite method. This suite thus provides a rare glimpse into the Mesoproterozoic mantle of the Superior Craton. Two parageneses of mantle material unrelated to the kimberlite magmatism occur: (1) an olivine + ilmenite ± magnetite association characterized by relatively Fe-rich olivine (Mg# = 0.68-0.84) and ilmenite enriched in Mg and Cr (4-13 wt.% MgO, Cr2O3 up to 3 wt.%), and (2) spinel peridotite characterized by Mg-rich olivine (Mg# = 0.91-0.94). The Fe-rich association is interpreted as a magmatic cumulate likely unrelated to the kimberlite. No mantle-derived garnet occurs in the xenoliths or as xenocrysts. The presence of Cr-rich spinel (Cr# = 0.84-0.98) in high temperature (860-953 °C) chromite peridotite indicates bulk compositions too depleted in Al for garnet to be stable, although geothermometry suggests they equilibrated at depths corresponding to garnet stability (90-131 km, depending on the geothermal gradient). Alternatively, the presence of phlogopite in two of the three high temperature (i.e., deepest) chromite peridotites suggests the absence of garnet and presence of low-Al chromite may have been caused by metasomatism from a K-rich fluid that replaced garnet with phlogopite + clinopyroxene ± chromite. Less depletion at shallower depths is indicated by a chromite (Cr# = 0.60) dunite that equilibrated at 831 °C and a low temperature (752 °C) Mg-Al-spinel lherzolite.
DS202006-0954
2020
Van Zyl, H.J., Bam, W.G., Steenkamp, J.D.Identifying barriers to growth in mineral value chains. ( not specific to diamonds)Journal of the Southern African Institute of Mining and Metallurgy, 8p. PdfAfrica, South Africalegal

Abstract: Despite the importance that barrier identification has for policy-making and industry stakeholders alike; little guidance exists on consistent processes to systematically identify barriers that are hindering the different sectors of a value chain’s expansion and growth. This article describes the development of a framework that supports the identification of barriers to growth in mineral value chains. The resultant process was applied to the case of the manganese value chain in South Africa, and revealed 31 barriers within this industry. The results were validated by a panel of experts and the feedback was used to rework and improve the framework.
DS202010-1883
2019
Vasilev, E., Kozlov, A.V.Hydrogen in diamond and a thermal history of diamond crystals. *** abst engResearchgate *** in Russ, 13p. Pdf 330360071MantleFTIR

Abstract: We have performed an analysis of the cases of synchronism in th egrowth temperature in local zones of diamond crystals and the concentration of hydrogen in them.The considered cases were observed by the authors and fined out in the iterature. Possible causes of the simbatic change in the crystal growth temperature and the concentration of hydrogen in it are considered.The determination of the temperature change over the zones was carried out on the basis of local FTIR spectroscopy from the ratio of the nitrogen concentration in the form of defects in the crystal structure of A and B1, and size the B2 defects.The change in the hydrogen concentration in various zones of diamond crystals was estimated from the 3107cm-1 band of the hydrogen-containing defect. It is shown that in the analyzed cases the concentration of hydrogen in diamond is determined mainly by its content in the growth medium.We accept the obtained results as evidence of the participation of hydrogen in the heat transfer in mantle mineral-forming systems.
DS202008-1454
2020
Vasilev, E., Kriulina, G., Klepikov, I.Luminescence of natural diamond in the NIR range.Physics and Chemistry of Minerals, Vol. 47, 31 6p. PdfRussialuminesence

Abstract: Natural diamond remains the source of many interesting effects and finds that are difficult to reproduce or detect in synthetic crystals. Herein, we investigate the photoluminescence (PL) of more than 2000 natural diamonds in the range 800-1050 nm. PL spectra were registered with excitation at 405, 450, 488 (Ar+), and 787 nm. The investigation revealed several systems that were not previously described. Some new dislocation-related systems were discovered in the spectra of crystals with signs of plastic deformation. They are four sets of doublets 890/900.3 nm, 918/930 nm, 946.5/961.5 nm, and 981/994 nm; four lines at 946, 961.5, 986, and 1020 nm. In low-nitrogen diamonds, they are accompanied by a line at 921 nm. Unreported vibronic systems with zero-phonon lines at 799.5, 819.6, 869.5, and 930 nm were revealed. In most cases, the systems were accompanied with doublet 883/885 of the simplest Ni-related center. We assigned these systems to Ni-related centers of different complexity. The results expand opportunities to restore growth conditions and thermal history of diamond crystals. The detection of new shallow centers expands the prospects of diamond as an optic and semiconductor material for applications in the NIR range.
DS202004-0540
2019
Vasilev, E.A., Klepikov, I.V., Kozlov, A.V., Antonov, A.V.The nature of the elongated form of diamond crystals from Urals ( Russia) placers.Journal of Mining Institute * not sure if in english?, Vol. 239, 5, pp. 492-496.Russiadiamond crystallography

Abstract: The article presents the results of a study of the internal structure of highly elongated diamond crystals from placers in the Krasnovishersky district of the Urals. Very elongated crystals are found within diamond-bearing placer with unrevealed primary sources. Determining the conditions of such crystals formation can help one to determine the primary deposits type. There are three hypotheses for the formation of the elongated shape of such crystals: 1) crystals initially elongated along the <100> (strongly distorted octahedra); 2) individual crystals of columnar aggregates; 3) elongated crystals fragments. To study the internal structure, we selected three most elongated individuals of the 155 crystals samples. The study of the internal structure of selected crystals with the usage of photoluminescent (PL) tomography, cathodoluminescence (CL), and optical microscopy has shown that these samples are fragments of larger single crystals. CL imaging allowed to determine slip lines within the crystal's volume. The recorded PL spectra show the 912, 946, and 986 nm peaks, which are characteristic of crystals with plastic deformation. The revealed features are indicators of plastic deformation accompanying the destruction of the crystals. The significant dissolution following the destruction of the crystals led to the rounding of the vertices and edges of their fragments. Apparently, most of the very elongated crystals from placers with unknown sources are also highly dissolved isometric crystal fragments. The obtained results have shown that the deformation and dissolution of diamond crystals are related events characteristic of diamonds from hitherto undetected, but highly productive primary deposits.
DS202003-0368
2019
Vasilev, E.A., Klepikov, I.V., Lukianova, L.I.Comparison of diamonds from the Rassolninskaya depression and modern alluvial placers of the Kranovishersky district ( Ural region).Geology of Ore Deposits, Vol. 61, 7, pp. 598-605. pdfRussia, Uralsdiamond morphology

Abstract: Three hundred thirty-six diamonds from deposits of the Rassolninskaya depression and 144 crystals from recent alluvial placers of the Krasnovishersky district were studied by IR absorption and photoluminescence spectroscopy. It is shown that crystals from the Rassolninskaya depression have a close-to-normal distribution for the nitrogen concentration. The average nitrogen content is 725 ppm, and no nitrogen-free crystals were detected. A sampling from recent alluvial placers contains 25% crystals with a nitrogen concentration smaller than 150 ppm; 3% of them are nitrogen-free. Among crystals from the Rassolninskaya depression, 12% are octahedral, 80% rhombododecahedral, and only one crystal has relicts of cubic faces. The collection from recent placers contains 3% cubic crystals, 10% individuals with relicts of cubic faces, 16% octahedroids, and 66% dodecahedra. Alluvial diamonds are often encountered with crescent-shaped cracks; however, they were observed only on a single crystal from the Rassolninskaya depression. It has been revealed that among alluvial placer diamonds, up to 95% of crystals contain nitrogen in the form of B1 defects. Thus, first, in morphological and structural-mineralogical features, diamonds from the Rassolninskaya depression differ from crystals of the nearest recent alluvial placers; second, they may belong to primary deposits based on the set of their characteristics.
DS202008-1455
2020
Vasilyev, P., McInnes, B., Reddicliffe, T.Evaluation of the source of diamonds and other kimberlitic minerals from the Webb kimberlite field, western Australia.Goldschmidt 2020, 1p. AbstractAustralia, Western Australiadeposit - Webb

Abstract: play located ~600 km west of Alice Springs in a remote region of WA. Exploration by GeoCrystal Ltd has identified more than 280 ‘bulls-eye’ magnetic features over a ~400 km2 area. Reconnaissance drilling of some of these features has returned mineral samples of kimberlite affinity, while surface sampling has recovered detrital microdiamonds with the number of inclusions, later analysed with FIBSEM. The unaltered diamond indicator minerals from drill samples analysed include: (i) G9 garnet predominating over G10; (ii) olivine ranging from Fo84-Fo91; (iii) Crdiopside (0.8-1.8% Cr2O3) and (iv) a broad range of Cr-Al spinel. A thermobarometric assessments of mineral chemistry data [1-3] show good agreement with each other and indicate a mantle origin for number of northern targets, including ones at possible equilibrium within the diamond stability field (P=45-50 kbar; T=1150- 1170°C). These results contain important information about the understudied deep lithosphere of Central Australia region.
DS202008-1456
2018
Vercoe, S., Lock, N.Our Jwaneng story.Botswana Journal of Earth Sciences, Vol. 7, pp. 3-12. pdfAfrica, Botswanadeposit - Jwaneng

Abstract: When Leon Daniels first contacted us, and others, about the Botswana Diamond Exploration Conference 2017, he wrote: ‘The future of diamond exploration lies in us "old-timers" who have retired or are about to retire to inspire the next generation to go out there and make the next discoveries so vitally important for Botswana.’ Sadly, in presenting on behalf of both Stuart and I, I had to own to being one of those old-timers!
DS202003-0369
2019
Vertriest, W., Palke, A.C., Renfro, N.D.Field gemology: building a research collection and understanding the development of gem deposits.Gems & Gemology, Vol. 55, 4, pp. 490-511.United StatesGIA

Abstract: GIA’s field gemology program was established in late 2008 to support research on geographic origin determination of colored gemstones. By building and maintaining an extensive collection of gem materials with known origins, GIA’s research scientists have been able to study and analyze rubies, sapphires, emeralds, and other gemstones using the best available reference samples. This has led to improved origin determination services while supporting numerous research and education projects. To date the collection has accumulated during more than 95 field expeditions on six continents and currently includes more than 22,000 samples. GIA’s field gemology efforts require a thorough understanding of the gem trade, including the evolution of gemstone deposits and the development of treatments. It is important to recognize potential new deposits and gemstone enhancement procedures immediately because they can change rapidly and leave a lasting impact on the trade. Field expeditions also involve documenting the mines and local conditions. These factors provide context for the gemstones and are becoming increasingly important in the eyes of the public.
DS202003-0370
2019
Vetrin, V.R.Isotopic geochemical systematics ( Sm-Nd, Lu-Hf) of Neoarchean subalkaline and alkaline rocks of the Keivy structure ( Kola Peninsula): their age and genetic relations.Geology of Ore Deposits, Vol. 61, 7, pp. 581-588. pdfRussia, Kola Peninsulamagmatism

Abstract: The Neoarchean subalkaline magmatism of the Keivy structure is expressed in the formation of the volcanoplutonic latite-monzonite-granite association (LMGA). The formation of LMGA magmas is assumed to occur due to melting of metasomatically altered mafic rocks during intrusion into the lower crust of basaltic melts initial for rocks of the dike complex and gabbro-labradorite massifs. The alkaline granites associated with LMGA have a close U-Pb age but a later formation time based on the geological data. With respect to LMGA, alkali granites have increased concentrations of SiO2, alkalis (K2O/Na2O = 1.1-1.4), iron (F# = 84-98%), a high agpaitic index (Kagp = 0.86-1.2), and lower quantities of TiO2, MgO, Fetot, and Al2O3, which probably resulted from the higher degree of differentiation of their initial melts compared to LMGA.
DS202009-1673
2020
Volante, S., Pouteau, A., Collins, W.J., Blereau, E., Li, Z-X., Smit, M., Evans, N.J., Nordsvan, A.R., Spencer, C.J., McDonald, B.J., Li, J., Gunter, C.Multiple P-T-d-t paths reveal the evolution of the final Nuna assembly in northeast Australia. Georgetown InlierJournal of Metamorphic Geology, Vol. 38, pp. 593-627.Australiageochronology

Abstract: The final assembly of the Mesoproterozoic supercontinent Nuna was marked by the collision of Laurentia and Australia at 1.60 Ga, which is recorded in the Georgetown Inlier of NE Australia. Here, we decipher the metamorphic evolution of this final Nuna collisional event using petrostructural analysis, major and trace element compositions of key minerals, thermodynamic modelling, and multi?method geochronology. The Georgetown Inlier is characterised by deformed and metamorphosed 1.70-1.62 Ga sedimentary and mafic rocks, which were intruded by c. 1.56 Ga old S?type granites. Garnet Lu-Hf and monazite U-Pb isotopic analyses distinguish two major metamorphic events (M1 at c. 1.60 Ga and M2 at c. 1.55 Ga), which allows at least two composite fabrics to be identified at the regional scale—c. 1.60 Ga S1 (consisting in fabrics S1a and S1b) and c. 1.55 Ga S2 (including fabrics S2a and S2b). Also, three tectono?metamorphic domains are distinguished: (a) the western domain, with S1 defined by low?P (LP) greenschist facies assemblages; (b) the central domain, where S1 fabric is preserved as medium?P (MP) amphibolite facies relicts, and locally as inclusion trails in garnet wrapped by the regionally dominant low?P amphibolite facies S2 fabric; and (c) the eastern domain dominated by upper amphibolite to granulite facies S2 foliation. In the central domain, 1.60 Ga MP-medium?T (MT) metamorphism (M1) developed within the staurolite-garnet stability field, with conditions ranging from 530-550°C at 6-7 kbar (garnet cores) to 620-650°C at 8-9 kbar (garnet rims), and it is associated with S1 fabric. The onset of 1.55 Ga LP-high?T (HT) metamorphism (M2) is marked by replacement of staurolite by andalusite (M2a/D2a), which was subsequently pseudomorphed by sillimanite (M2b/D2b) where granite and migmatite are abundant. P-T conditions ranged from 600 to 680°C and 4-6 kbar for the M2b sillimanite stage. 1.60 Ga garnet relicts within the S2 foliation highlight the progressive obliteration of the S1 fabric by regional S2 in the central zone during peak M2 metamorphism. In the eastern migmatitic complex, partial melting of paragneiss and amphibolite occurred syn? to post? S2, at 730-770°C and 6-8 kbar, and at 750-790°C and 6 kbar, respectively. The pressure-temperature-deformation-time paths reconstructed for the Georgetown Inlier suggest a c. 1.60 Ga M1/D1 event recorded under greenschist facies conditions in the western domain and under medium?P and medium?T conditions in the central domain. This event was followed by the regional 1.56-1.54 Ga low?P and high?T phase (M2/D2), extensively recorded in the central and eastern domains. Decompression between these two metamorphic events is ascribed to an episode of exhumation. The two?stage evolution supports the previous hypothesis that the Georgetown Inlier preserves continental collisional and subsequent thermal perturbation associated with granite emplacement.
DS202005-0768
2020
Voosen, P.Diamond microscope reveals slow crawl of Earth's ancient crust. QDM sciencemag.org, April 22, 3p.Globalmeteorites, nitrogen
DS202008-1457
2020
Vorobei, S.S., Garanin, V.K., Minervina, E.A., Posukhova, T.V., Weisheng, X.The mineralogy and geochemistry of mantle xenoliths from diamondiferous kimberlite of China and Russia.Moscow University Geology Bulletin, Vol. 75, 2, pp. 128-135. pdfRussia, Chinadeposit - Mir, Shandong, Liaoning

Abstract: enoliths from the Mir pipe and from the Shandong and Liaoning provinces were studied by the methods of EMPA and ICP-MS. Their mineralogical, geochemical, and genetic features were revealed. Minerals of diamondiferous paragenesis were detected in xenoliths from the Mir pipe, while they were not found in xenoliths of China. All xenoliths are characterized by secondary alterations, which are more intense in xenoliths of China. The distribution of REEs shows the involvement of subduction processes in the formation of xenoliths from the Mir pipe. The influence of metasomatism is clearly evident in xenoliths from China. The calculated P-T parameters (? = 600-700°C, P = 2-2.5 GPa) are not consistent with the mantle environments that correspond to the metasomatic conditions.
DS202005-0769
2020
Vrublevskii, V.V., Nikiforov, A.V., Sugorakov, A.M., Kozulina, T.V.Petrogenesis and tectonic setting of the Cambrian Kharly alkaline-carbonatite complex ( Sangilen Plateau, southern Siberia): implications for the early Paleozoic evolution of magmatism in the western Asian orogenic belt.Journal of Asian Earth Sciences, Vol. 188, 26p. PdfRussia, Siberiacarbonatite

Abstract: The Cambrian Kharly alkaline plutonic complex composed mainly of foidolite and nepheline syenite makes up a small intrusive field in the Sangilen Plateau in Tuva (southern Siberia). The rocks show large ranges of major oxides (38-58 wt% SiO2; 1-18 wt% Na2O + K2O; 11-28 wt% Al2O3; 1.5-20 wt% CaO; 0.1-8 wt% MgO; 2-12 wt% Fe2O3) controlled by variable percentages of minerals: clinopyroxenes, calcic amphiboles, micas, nepheline and feldspars. Alkaline rocks are cut by carbonatite veins composed of predominant calcite coexisting with femic minerals (10-15% of aegirine-ferrosalite-hedenbergite, sodic-calcic amphiboles, ferrobiotite, Ti-garnet), Na-K feldspar and nepheline (up to 15-20%), fluorapatite (up to 20-25%), Sr-apatite, and accessory carbocernaite, titanite, Ti-magnetite and ilmenite. Carbonatites (4057-8859 ppm Sr, 426-1901 ppm Ba (Sr/Ba ? 2), 290-980 ppm REE + Y, 2 to 100 ppm Zr, and 0.5 to 15 ppm Nb) possibly originated at high (?500-650 °C) temperatures as a result of liquid immiscibility. The isotope systematics of rocks and minerals (?Nd(t) from ~2.9 to 6.5; 207Pb/206Pbin = 0.89; 208Pb/206Pbin = 2.15; 87Sr/86Sr(t) = 0.70567-0.70733, ?18OV-SMOW ? 7.2-19.5‰, and ?13CV-PDB from ?6.0 to ?1.4‰) suggest mixing of PREMA and EM 1 material during magma generation and crustal contamination of the evolving melts. The rocks bear signatures of interaction with “magmatic-equilibrated” fluids or heated meteoric waters. LILE/HFSE ratios indicate mixed magma sources that involved the material of IAB and OIB, as well as a crustal component, possibly, due to interaction of a mantle plume with rock complexes on the active continental margin.
DS202006-0955
2020
Walter, B.F., Steele-MacInnis, M., Giebel, R.J., Marks, M.A.W., Markl, G.Complex carbonatite-sulfate brines in fluid inclusions from carbonatites: estimating compositions in the system H2O-Na-K-CO3-SO4-Cl. KaiserstuhlGeochimica et Cosmochimica Acta, Vol. 277, pp. 224-242. pdfEurope, Germanycarbonatite

Abstract: Studies of fluid inclusions in carbonatitic rocks are essential for understanding physicochemical processes involved in carbonatite-related hydrothermal ore mineralization and fenitization. However, the composition of many carbonatite-derived fluids is challenging to quantify, which hampers their detailed interpretation. Here, we present a systematic study of microthermometry of fluid inclusions found in carbonatites from the Kaiserstuhl (SW Germany), and a simple numerical model to estimate the compositions of such fluids, which are typical of numerous carbonatites worldwide. Four types of fluid inclusions have been identified in the Kaiserstuhl carbonatites: (I) vapor-poor H2O-NaCl fluids with <50?wt.% salinity; (II) vapor-rich H2O-NaCl-CO2 fluids with <5?wt.% salinity; (III) multi-component fluids with high salinity and high CO2 contents; and (IV) multi-component fluids with high salinity but little to no CO2. At present, it is only possible to quantify fluid compositions for types I and II. For the complex types III and IV, we conducted predictive modeling of the liquidus surface based on the Margules equations. The results suggest that carbonatite melts predominantly exsolve Na-K-sulfate-carbonate/bicarbonate-chloride brines (types III or IV). Such fluid inclusions may represent immiscible fluids that were trapped after segregation by boiling from a parental highly saline brine (type I). Fluid boiling, in turn, was probably triggered by a rapid pressure release during melt ascent. The present model enables quantification of fluid compositions associated with carbonatitic magmatism.
DS202007-1184
2020
Walter, B.F., Steele-MacInnis, M., Gielbel, R.J., Marks, M.A.W., Markl, G.Complex carbonatite-sulfate brines in fluid inclusions from carbonatites: estimating compositions in the system H2O-Na-K-CO3-SO4-ClGeochimica et Cosmochimica Acta, Vol. 277, pp. 224-242. pdfEurope, Germanydeposit - Kaiserstuhl

Abstract: Studies of fluid inclusions in carbonatitic rocks are essential for understanding physicochemical processes involved in carbonatite-related hydrothermal ore mineralization and fenitization. However, the composition of many carbonatite-derived fluids is challenging to quantify, which hampers their detailed interpretation. Here, we present a systematic study of microthermometry of fluid inclusions found in carbonatites from the Kaiserstuhl (SW Germany), and a simple numerical model to estimate the compositions of such fluids, which are typical of numerous carbonatites worldwide. Four types of fluid inclusions have been identified in the Kaiserstuhl carbonatites: (I) vapor-poor H2O-NaCl fluids with <50?wt.% salinity; (II) vapor-rich H2O-NaCl-CO2 fluids with <5?wt.% salinity; (III) multi-component fluids with high salinity and high CO2 contents; and (IV) multi-component fluids with high salinity but little to no CO2. At present, it is only possible to quantify fluid compositions for types I and II. For the complex types III and IV, we conducted predictive modeling of the liquidus surface based on the Margules equations. The results suggest that carbonatite melts predominantly exsolve Na-K-sulfate-carbonate/bicarbonate-chloride brines (types III or IV). Such fluid inclusions may represent immiscible fluids that were trapped after segregation by boiling from a parental highly saline brine (type I). Fluid boiling, in turn, was probably triggered by a rapid pressure release during melt ascent. The present model enables quantification of fluid compositions associated with carbonatitic magmatism.
DS202001-0046
2019
Wang, D., Romer, R.L., Guo, J-h., Glodny, J.Li and B isotopic fingerprint of Archean subduction.Geochimica et Cosmochimica Acta, in press available pdf 45p.Chinacraton

Abstract: Archean peridotite xenoliths in the ?2.52?Ga Zhulagou diorite (Yinshan Block, North China Craton) show chemical and Li isotopic evidence for metasomatism above an ancient subduction zone. The peridotite xenoliths are composed of olivine?+?orthopyroxene?+?amphibole?+?phlogopite?+?serpentine. The peridotite xenoliths have low whole-rock Mg# (80-81) and low Mg# (81-84) in olivine, indicating that they are cumulates that formed near the crust-mantle boundary. Petrological observations, mineral trace element data and isotopic ages show that the sequence of hydrous minerals is amphibole-serpentine-phlogopite. SIMS U-Pb dating of zircon from peridotites yielded an upper intercept age at ?2.53?Ga, and a U-Pb lower intercept age at ?1.8?Ga. The age of ?2.53?Ga is interpreted to date the crystallization of zircon from the metasomatized mantle melt that formed the Zhulagou cumulate peridotite. Rb-Sr mineral isochrons date phlogopite formation at ?1760?Ma, consistent with the lower intercept age of zircon. Pargasitic amphibole from the Zhulagou peridotites has fractionated REE, pronounced depletions of Nb, Ta, Zr and Ti, and heavy ?7Li (?+14‰) and light ?11B (?-11‰). Combined with slightly depleted mantle whole rock ?Nd (?+1.3) and high zircon ?18O (+5.6 to +7.0‰), the amphibole composition reflects that the peridotite xenoliths formed from melts that carried the geochemical and isotopic fingerprint typical for a metasomatized mantle wedge above a subduction zone. The Zhulagou peridotite xenoliths have the highest ?7Li values (?+12‰) recorded in Archean peridotites. Isotopically heavy Li and light B in olivine, orthopyroxene, and amphibole from the peridotite xenoliths show that Li and B may decouple during partial melting or fluid release from the subducted slab. The decoupling of Li and B may have a variety of reasons, including different host minerals for Li and B in the source and different protoliths in the subducted slab. The Li and B isotopic record on the recycling of ancient material demonstrates that modern-style subduction operated already in the late Archean.
DS202006-0956
2020
Wang, K., Guo, R., Zhang, Y., Tian, Y.Photoluminescence and annealing of nitrogen-interstitials defects in electron irradiated diamond.Spectroscopy Letters, Vol. 53, 4, pp. 270-276.Globalluminescence

Abstract: There are a few studies reported in the literature describing the conversion of intrinsic defects but the involvement of nitrogen-interstitials in diamond has not been reported so far. In this paper, a detailed study on the conversion of nitrogen-interstitials in diamond during the irradiation and further annealing were presented by the micro-photoluminescence spectra. The results indicated that the interstitials were immobile until 300?°C and then escaped from the nitrogen capture, followed by migration and recombination with vacancies in the structure of nitrogen-vacancy and vacancy centers.
DS202004-0541
2019
Wang, W., Cai, L.Inclusion extraction from diamond clarity images based on the analysis of diamond optical properties.Optics Express, Vol. 27, 19, pp. 27242-27255. doi.org/10.1034/ oe.27.027242Globaldiamond inclusion

Abstract: Diamond clarity refers to the absence of tiny, natural inclusions (imperfections) inside a diamond or on its surface. Almost all diamonds contain their own unique inclusions due to their natural formation process. In this paper, a new inclusion extraction approach is developed to accurately separate the regions of interest in a diamond clarity image and then identify the image features of each region. The inclusion regions can be successfully distinguished from other types of signals. The findings of the theoretical optical analysis facilitate the image processing development and also reduce its complexity and operation time. The experimental results verify the effectiveness and robustness of the proposed inclusion extraction approach. The diamond inclusions can be accurately extracted from the captured diamond clarity image. The extracted inclusions can also be converted to their actual size as seen by the naked human eye. The proposed approach is verified to be significantly less sensitive to noise than existing approaches and unaffected by the fluctuations in illumination.
DS202001-0047
2020
Wang, X., Xiao, Y., Sun, Y., Wang, Y., Liu, J., Yang, K., Gu, H., Hou, Z., Tian, Y., Wu, W., Ma, Y.Initiation of the North China craton destruction: constraints from the diamond bearing alkaline basalts from Langan, China.Gondwana Research, Vol. 80, pp. 228-243.Chinacraton

Abstract: The North China Craton (NCC) is an atypical ancient landmass that suffered lithospheric destruction. Previous studies suggest that the eastern part of the lithospheric mantle of the NCC has been thinned and modified in the Mesozoic. However, the initiation time and mechanism of the destruction remain controversial. Mafic magmatismcould provide a unique windowinto deciphering the lithospheric mantle composition and its evolution. Here we present geochemical and geochronological data of the diamond-bearing alkaline basalts from Lan'gan, located in the southeastern margin of the NCC. Zircon U-Pb dating yielded an average age of 174 ± 14 Ma, representing the first reported Jurassic basalts in the eastern NCC. The Lan'gan basalts are enriched in light rare earth elements (LREE) and large ion lithosphile elements (LILE). Sr-Nd-Pb-Hf isotopic compositions (87Sr/86Sr(t) = 0.70646-0.70925, ?Nd(t) = ?2.1 to ?4.9, 206Pb/204Pb(t) = 17.14-18.12, 207Pb/204Pb(t) = 15.28-15.61, 208Pb/204Pb(t) = 37.82-38.67, and zircon ?Hf(t) = ?17 to ?21) are enriched compared to depleted mantle. The presence of primary amphibole indicates that the magma source of the basalts was water enriched. These observations suggest that, the lithospheric mantle of the eastern NCC were significantly refertilized, likely by slab derived fluids/melts fromthe Paleo-Pacific subduction. Owing to the Paleo-Pacific subduction, the lithosphericmantle of the eastern NCCwere reduced in viscosity and intensity, and finally promoted partialmelting in a limited scale to generate the investigated alkaline basalts. Hence, the discovery of diamond in the Lan'gan basalts demonstrates that the lithosphere of the NCC remained thick, and that large-scale destruction had not initiated in the early Jurassic beneath this region.
DS202004-0542
2020
Wang, X., Xiao, Y., Wang, Y., Liu, J., Yang, K., Gu, H., Hou, Z., Tian, Y., Wu, W., Ma, Y.Initiation of the North China Craton destruction: constraints from the diamond bearing alkaline basalts from Langan China.Gondwana Research, Vol. 80, pp. 228-243.Chinadeposit - Langan

Abstract: The North China Craton (NCC) is an atypical ancient landmass that suffered lithospheric destruction. Previous studies suggest that the eastern part of the lithospheric mantle of the NCC has been thinned and refertilized in the Mesozoic. However, the initiation time and mechanism of the destruction remain controversial. Mafic magmatism could provide a unique window into deciphering the lithospheric mantle composition and its evolution. Here we present geochemical and geochronological data of the diamond-bearing alkaline basalts from Lan'gan, located in the southeastern margin of the NCC. Zircon UPb dating yielded an average age of 174?±?14?Ma, representing the first reported Jurassic basalts in the eastern NCC. The Lan'gan basalts are enriched in light rare earth elements (LREE) and large ion lithosphile elements (LILE). Sr-Nd-Pb-Hf isotopic compositions (87Sr/86Sr(t)?=?0.70646-0.70925, ?Nd(t)?=??2.1 to ?4.9, 206Pb/204Pb(t)?=?17.14-18.12, 207Pb/204Pb(t)?=?15.28-15.61, 208Pb/204Pb(t)?=?37.82-38.67, and zircon ?Hf(t)?=??17 to ?21) are slightly enriched compared to depleted mantle. The presence of primary amphibole indicates that the magma source of the basalts was water enriched. These observations suggest that, the lithospheric mantle of the eastern NCC were significantly refertilized, likely by slab derived fluids/melts from the Paleo-Pacific subduction. Owing to the Paleo-Pacific subduction, the lithospheric mantle of the eastern NCC were reduced in viscosity and intensity, and finally promoted partial melting in a limited scale to generate the investigated alkaline basalts. Hence, the discovery of diamond in the Lan'gan basalts demonstrates that the lithosphere of the NCC remained thick, and that large-scale destruction had not initiated in the early Jurassic beneath this region.
DS202012-2254
2020
Wang, Z-Y., Fan, H-R., Zhou, L., Yang, K-F., She, H-D.Carbonatite-related REE deposits: an overview.MDPI Minerals, Vol. 10, 965 doi:103390/min10110965, 26p. PdfChinacarbonatite, REE

Abstract: The rare earth elements (REEs) have unique and diverse properties that make them function as an “industrial vitamin” and thus, many countries consider them as strategically important resources. China, responsible for more than 60% of the world’s REE production, is one of the REE-rich countries in the world. Most REE (especially light rare earth elements (LREE)) deposits are closely related to carbonatite in China. Such a type of deposit may also contain appreciable amounts of industrially critical metals, such as Nb, Th and Sc. According to the genesis, the carbonatite-related REE deposits can be divided into three types: primary magmatic type, hydrothermal type and carbonatite weathering-crust type. This paper provides an overview of the carbonatite-related endogenetic REE deposits, i.e., primary magmatic type and hydrothermal type. The carbonatite-related endogenetic REE deposits are mainly distributed in continental margin depression or rift belts, e.g., Bayan Obo REE-Nb-Fe deposit, and orogenic belts on the margin of craton such as the Miaoya Nb-REE deposit. The genesis of carbonatite-related endogenetic REE deposits is still debated. It is generally believed that the carbonatite magma is originated from the low-degree partial melting of the mantle. During the evolution process, the carbonatite rocks or dykes rich in REE were formed through the immiscibility of carbonate-silicate magma and fractional crystallization of carbonate minerals from carbonatite magma. The ore-forming elements are mainly sourced from primitive mantle, with possible contribution of crustal materials that carry a large amount of REE. In the magmatic-hydrothermal system, REEs migrate in the form of complexes, and precipitate corresponding to changes of temperature, pressure, pH and composition of the fluids. A simple magmatic evolution process cannot ensure massive enrichment of REE to economic values. Fractional crystallization of carbonate minerals and immiscibility of melts and hydrothermal fluids in the hydrothermal evolution stage play an important role in upgrading the REE mineralization. Future work of experimental petrology will be fundamental to understand the partitioning behaviors of REE in magmatic-hydrothermal system through simulation of the metallogenic geological environment. Applying "comparative metallogeny" methods to investigate both REE fertile and barren carbonatites will enhance the understanding of factors controlling the fertility.
DS202004-0543
2019
Ward, F., Ward, C.Diamonds. 4th editionGem Book Publishers Malibu CA, 64p. Isbn 978- 1887651189 US 19.95Globalbook
DS202001-0048
2019
Weisberger, M.Diamonds buried 400 miles below surface could explain mysterious earthquakes. Shirey's work on inclusionLiveScience.com, Dec. 18, 1/2p.Mantlediamond inclusions
DS202005-0770
2020
Weska, R.K., Ferreira Barbosa, P., Martins, M.V.C., Souza, V.S., Dantas, E.L.Pectolite in the Carolina kimberlitic intrusion, Espigao D'Oeste - Rondonia, Brazil. ( Pimenta Bueno field)Journal of South American Earth Sciences, Vol. 100, 10.1016/j.jsames.2020.102583 7p. PdfSouth America, Brazil, Rondoniadeposit - Carolina

Abstract: In this study, we characterize pectolite that occurs in a Carolina kimberlitic intrusion from the Pimenta Bueno Kimberlite Field (PBKF). The PBKF is the only kimberlite field of Permo-Carboniferous age in Brazil and is found on the southern Amazonian Craton. Pectolite, an Na-Ca-silicate usually identified in alkaline rocks as a primary mineral, is not common in the mineral paragenesis of kimberlites and is described here for the first time in Brazil. The genesis of pectolite in kimberlite has been well-studied and can be interpreted as a primary or secondary mineral resulting from the infiltration of an Na-rich fluid into metasomatic reactions. In the rocks from the PBKF, pectolite mainly occurs as fibrous and radial aggregates enriched in K2O that grow between olivine partially altered to serpentine and phlogopite. The results of field and petrographic observations suggest that the PBKF pectolite is of secondary origin, having formed during the hydrothermal alteration of the Carolina kimberlitic intrusion.
DS202011-2067
2020
White-Gaynor, A.L., Nyblade, A.A., Durrheim, R., Raveloson, R., van der Meijde, M., Fadel, I., Paulssen, H., Kwadiba, M., Ntibinyane, O., Titus, N., Sitali, M.Lithospheric boundaries and upper mantle structure beneath southern Africa imaged by P and S wave velocity models.Geochemistry, Geophysics, Geosystems, 10.1029/GC008925 20p. PdfAfrica, South AfricaGeophysics, seismic

Abstract: We report new P and S wave velocity models of the upper mantle beneath southern Africa using data recorded on seismic stations spanning the entire subcontinent. Beneath most of the Damara Belt, including the Okavango Rift, our models show lower than average velocities (?0.8% Vp; ?1.2% Vs) with an abrupt increase in velocities along the terrane's southern margin. We attribute the lower than average velocities to thinner lithosphere (~130 km thick) compared to thicker lithosphere (~200 km thick) immediately to the south under the Kalahari Craton. Beneath the Etendeka Flood Basalt Province, higher than average velocities (0.25% Vp; 0.75% Vs) indicate thicker and/or compositionally distinct lithosphere compared to other parts of the Damara Belt. In the Rehoboth Province, higher than average velocities (0.3% Vp; 0.5% Vs) suggest the presence of a microcraton, as do higher than average velocities (1.0% Vp; 1.5% Vs) under the Southern Irumide Belt. Lower than average velocities (?0.4% Vp; ?0.7% Vs) beneath the Bushveld Complex and parts of the Mgondi and Okwa terranes are consistent with previous studies, which attributed them to compositionally modified lithosphere resulting from Precambrian magmatic events. There is little evidence for thermally modified upper mantle beneath any of these terranes which could provide a source of uplift for the Southern African Plateau. In contrast, beneath parts of the Irumide Belt in southern and central Zambia and the Mozambique Belt in central Mozambique, deep?seated low velocity anomalies (?0.7% Vp; ?0.8% Vs) can be attributed to upper mantle extensions of the African superplume structure.
DS202010-1884
2020
Wiedendorfer, D., Manning, C.E., Schmidt, M.W.Carbonate melts in the hydrous upper mantle.Contributions to Mineralogy and Petrology, doi.org/10.1007/ s00410-020-01708 17p. Pdf Mantlecarbonatite

Abstract: Carbonatite compositions resulting from melting of magnesian calcite?+?olivine?+?clinopyroxene were experimentally determined in the system CaO-MgO-SiO2-CO2-H2O as a function of temperature and bulk H2O contents at 1.0 and 1.5 GPa. The melting reaction and melt compositions were found to be highly sensitive to H-loss or -gain during experiments. We hence designed a new hydrogen-trap technique, which provided sufficient control to obtain consistent results. The nominally dry solidus temperatures at 1.0 and 1.5 GPa are 1225-1250 °C and 1275-1300 °C, respectively. At 1.0 GPa, the solidus temperature decreases with H2O increasing to 3.5 wt% (1025-1050 °C), then remains approximately constant at higher H2O concentrations. Our nominally dry solidus temperatures are up to 140 °C higher than in previous studies that did not take measures to limit hydrogen infiltration and hence suffered from H2O formation in the capsule. The near-solidus anhydrous melts have 7-8 wt% SiO2 and molar Ca/(Ca?+?Mg) of 0.78-0.82 (XCa). Melting temperatures decrease by as much as 200 °C with increasing XH2O in the coexisting COH-fluid. Concomitantly, near-solidus melt compositions change with increasing bulk H2O from siliceous Ca-rich carbonate melts to Mg-rich silico-carbonatites with up to 27.8 wt% SiO2 and 0.55 XCa. The continuous compositional array of Ca-Mg-Si carbonatites demonstrates the efficient suppression of liquid immiscibility in the alkali-free system. Diopside crystallization was found to be sensitive to temperature and bulk water contents, limiting metasomatic transformation of carbonated upper mantle to wehrlite at 1.0-1.5 GPa to?
DS202004-0544
2020
Will, T.M., Hohn, S., Frimmel, H.E., Gaucher, C., Le Roux, P.J., Macey, P.H.Petrological, geochemical and isotopic data of Neoproterozoic rock units from Uruguay and South Africa: correlation of basement terranes across the South Atlantic.Gondwana Research, Vol. 80, pp. 12-32.South America, Uruguay, Brazil, Africa, Namibiacraton

Abstract: Felsic to intermediate igneous rocks from the Cuchilla Dionisio (or Punta del Este) Terrane (CDT) in Uruguay and the Várzea do Capivarita Complex (VCC) in southern Brazil were emplaced in the Tonian and experienced high-grade metamorphism towards the end of the Cryogenian. Geological and geochemical data indicate an S-type origin and formation in a continental within-plate setting by recycling of lower crustal material that was initially extracted from the mantle in the Palaeoproterozoic. Similar felsic igneous rocks of Tonian age occur in the Richtersveld Igneous Complex and the Vredefontein and Rosh Pinah formations in westernmost South Africa and southern Namibia and have been correlated with their supposed equivalents in Uruguay and Brazil. Geochemical and isotope data of the largely unmetamorphosed felsic igneous rocks in southwestern Africa imply a within-plate origin and formation by partial melting or fractional crystallization of mafic rocks that were extracted from the mantle in the Proterozoic. The parental melts of all of these Tonian igneous rocks from South America and southwestern Africa formed in an anorogenic continental setting at the western margin of the Kalahari Craton and were emplaced in, and/or contaminated by, Namaqua Province-type basement after separation from their source region. However, the source regions and the time of extractions thereof are different and, moreover, occurred at different palaeogeographical latitudes. New petrological data of CDT high-grade gneiss indicate a geothermal gradient of c. 20-25 °C/km, implying continental collisional tectonics following subduction and ocean basin closure at an active continental margin at the eastern edge of present-day South America in the late Cryogenian to early Ediacaran. The associated suture may be traced by the high-grade gneiss and amphibolite-facies mafic rocks in the CDT and probably continues northwards to the Arroio Grande Complex and the VCC in southern Brazil.
DS202012-2255
2020
Windley, B.F., Kusky, T., Polat, A.Onset of plate tectonics by the Eoarchean. ( accretionary and collisional)Precambrian Research, in press available, 43p. PdfMantleplate tectonics

Abstract: One of the most contentious areas of Earth Science today is when, or whether or not modern-style plate tectonics was in operation in the Archean Eon. In this review we present evidence that the onset of plate tectonics was not at 3.2 Ga, as popularly conceived, but was in operation during the Eoarchean by at least ca. 4.0 Ga. Following a review of the main Eoarchean supracrustal belts of the world, constrained by relevant geochemical/isotopic data, we present evidence that suggests that from at least ca. 4.0 Ga Earth produced considerable juvenile mafic crust and consequent island arcs by Accretionary Cycle Plate Tectonics. From ~3.2 Ga there was a gradual transition in geodynamics to more abundant active continental margin magmatism in the form of voluminous TTGs and sanukitoids. From 3.2 Ga to 2.5 Ga juvenile oceanic crust and arcs continued to form, accompanied by more active continental margin magmatism until ~2.7-2.5 Ga, by which time there were sufficient crustal rocks to amalgamate into incipient large continents, the fragmentation of which started the first complete classical Wilson Cycle Plate Tectonics of breaking apart and re-assembling large continental masses. In other words, there were two types of plate tectonics in operation in the early Earth, Accretionary Cycle Plate Tectonics and Wilson Cycle Plate Tectonics, but Wilson Cycle type plate interactions only became more common after contiguous continental landmass became voluminous and extensive enough around 2.7-2.5 Ga. Failure to realize this dual mechanism of continental growth may lead to erroneous ideas such as "plate tectonics started at 3.2 Ga", or "mantle plumes generated early Archean magmatic rocks." We present new geochemical data that together with lithological and structural relationships, negate the various plume-type speculations including stagnant lids, heat pipes, and mushy-lid tectonics. It is interesting to consider that the way Earth’s crust developed in the first Gigayear of the geological record continued later, albeit in more advanced forms, into the Phanerozoic, where we can still recognize Accretionary Cycle Plate Tectonics and orogens still with short boundaries in examples including the Altaids of Central Asia, the Arabian-Nubian Shield, the Japanese Islands, and in incipient form in Indonesia, as well as Wilson Cycle Plate Tectonics that leads inexorably to continental collisions as in the Alpine-Himalayan orogen with its long plate boundaries. We recommend this holistic view of crustal growth and the evolution of continents that leads to a robust, viable, and testable model of Earth evolution.
DS202009-1674
2020
Wiszniewska, J.B., Krzeminska, E., Petecki, Z., Grababarczyk, A., Demaiffe, D.Geophysical and petrological constraints for ultramafic-alkaline-carbonatite magmatism in the Tajno intrusion, NE Poland.Goldschmidt 2020, 1p. AbstractEurope, Polandcarbonatites

Abstract: This Tajno alkaline massif (together with the nearby E?k and Pisz intrusions) occurs beneath a thick Mesozoic- Cenozoic sedimentary cover. It has first been recognized by geophysical (magnetic and gravity) investigations, then directly by deep drilling (12 boreholes down to 1800 m). The main rock types identified as clinopyroxenites, syenites, carbonatites, have been cut by later multiphase volcanic /subvolcanic dykes. This massif was characterized as a differentiated ultramafic, alkaline and carbonatite complex, quite comparable to the numerous massifs of the Late Devonian Kola Province of NW Russia [1,2]. Recent geochronological data (U-Pb on zircon from an albitite and Re-Os on pyrrhotite from a carbonatite) indicate that the massif was emplaced at ca. 348 Ma (Early Carboniferous). All the rocks, but more specifically the carbonatites, are enriched in Sr, Ba and LREE, like many carbonatites worldwide but depleted in high field strength elements (Ti, Nb, Ta, Zr). The initial 87Sr/86Sr (0.70370 to 0.70380) and ?Nd(t) (+3.3 to +0.7) isotopic compositions of carbonatites plot in the depleted quadrant of the Nd-Sr diagram, close to “FOcal ZOne” (FOZO) deep mantle domain [1]. The Pb isotopic data (206Pb/204Pb <18.50) do not point to an HIMU (high U/Pb) source. The ranges of C and O stable isotopic compositions of the carbonatites are quite large; some data plot in (or close to) the “Primary Igneous Carbonatite” box while others extend to much higher, typically crustal ?18O and ?13C values.
DS202005-0771
2020
Witherly, K.Geophysics - past performance and future opportunity. Review and comments( not specific to diamonds but interestsSEG Discovery ( former NewsLetter), No. 121, April pp. 40-41.Canada, AustraliaGeophysics
DS202001-0049
2019
Witze, A.Earth's magnetic field older than scientists thought.Nature, Vol. 576, Dec. 19/26, p. 347.Europe, Greenlandgeophysics - magnetics
DS202011-2068
2020
Woodruff, L.G., Schulz, K.J., Nicholson, S.W., Dicken, C.L.Mineral deposits of the Mesoproterozoic Midcontinent rift system in the Lake Superior region - a space and time classification. Not specific to diamondsOre Geology Reviews, Vol. 126, 103716, 21p. PdfCanada, United Statestectonics

Abstract: The Mesoproterozoic Midcontinent Rift System (MRS) of North America hosts a diverse suite of magmatic and hydrothermal mineral deposits in the Lake Superior region where rift rocks are exposed at or near the surface. Historically, hydrothermal deposits, such as Michigan’s native copper deposits and the White Pine sediment-hosted stratiform copper deposit, were major MRS metal producers. On-going exploration for and potential development of copper-nickel sulfide deposits hosted by the Duluth Complex of Minnesota and the opening of the Eagle nickel mine in Michigan indicate an expanding interest in MRS magmatic deposits. MRS hydrothermal and magmatic mineral deposits, many of which are significant past, present, and likely future providers of critical minerals, here are placed into a space and time metallogenic framework. To construct this framework, regional MRS mineral deposits extracted from the U.S. Geological Survey Mineral Resources Data System (MRDS) and the Ontario Ministry of Energy, Northern Development and Mines Mineral Deposit Inventory (MDI) were supplemented by other known and recently recognized mineral deposits described in the literature. All mineral deposits were classified by deposit type, host rock age and type, and estimated timing of mineralization. Deposits were then put into a tectonic evolutionary framework (stages) for the MRS, which shows that deposits formed within discrete spatial and temporal stages of rift evolution. Each stage of rift evolution is characterized by specific mineral deposit types that are largely confined both by their physical location in rift rocks and type and timing of mineralization. Examples include MRS nickel-rich conduit-type magmatic sulfide deposits, which are restricted to an early magmatic stage MRS history when magma compositions were characterized by Ni-rich picrites and high Mg basalts. In contrast, contact-type magmatic sulfide deposits with Cu > Ni were derived from more evolved Al-rich tholeiitic magmas that dominated a later time of voluminous magmatic activity. Hydrothermal sediment-hosted stratiform chalcocite mineralization along the margins of western Lake Superior in Michigan is economic only where fluid flow through red beds was concentrated by structures along the margins of a post-volcanic MRS sedimentary basin. Widespread native Cu and native Ag mineralization occurred about 40 million years after formation of host basalt lava flows and interflow sedimentary rocks. These descriptions of the diverse mineral deposits in the Lake Superior region cataloged within the space of the local and regional geology and over the more than 60-million-year mineralizing history of the MRS are indicative of the complex and at times overlapping magmatic and hydrothermal mineral systems that operated within this major large igneous province.
DS202004-0545
2020
Wright, L.J., M., Muirhead, J.D., Scholz, C.ASpatio-temporal variations in upper crustal extension across the different basement terranes of the Lake Tanganyika Rift, East Africa.Tectonics, Vol. 39, 3, doi:e2019TC006019Africacraton

Abstract: Preexisting crustal heterogeneities are shown to influence rift process at a variety of scales. However, our understanding of how crustal inheritance influences rift?scale spatiotemporal kinematics of faulting in magma?poor rift environments is still very limited. Studies of active continental rifts can provide high?fidelity assessments of extensional processes and structures that are not possible through examination of ancient rifts that have undergone subsequent deformation events or are buried deeply beneath passive margins. We examine the influence of crustal inheritance on active rifting through balancing and restoring a series of regional cross sections across the Lake Tanganyika Rift in the Western Branch of the East African Rift System. The cross sections are produced using legacy seismic reflection data, reprocessed through prestack depth migration. This type example of a young, magma?poor continental rift transects several different basement terranes, including an Archean/Paleoproterozoic craton, and Proterozoic mobile belts. The Lake Tanganyika Rift exhibits two classic bell?shaped profiles of extension along strike, reaching a maximum of 7.15 km. A spatiotemporal integration of the extension data, and comparison with the various basement terranes the rift transects, reveals that extension in cratonic blocks is more widely distributed compared to mobile belt terranes, where strain rapidly localizes onto border faults by later rift stages. These results reveal how crustal inheritance exerts a fundamental control on the evolution of extension localization, ultimately impacting the geometry and structural architecture of rift basins.
DS202004-0546
2020
Xiang, L., Zheng, J., Zhai, M., Siebel, W.Geochemical and Sr-Nd-Pb isotopic constraints on the origin and petrogenesis of Paleozoic lamproites in the southern Yangtze Block, south China.Contributions to Mineralogy and Petrology, Vol. 175, 18p. PdfChinalamproites

Abstract: Lamproites and kimberlites are natural probes of the subcontinental lithospheric mantle providing insights into the Earth’s continental lithosphere. Whole-rock major-, trace-element and Sr-Nd-Pb isotopic compositions of the Paleozoic (~?253 Ma) lamproite dikes from the Baifen zone of the Zhenyuan area in southeastern Guizhou Province (in the southern Yangtze Block, South China) are presented. The Baifen lamproites are characterized by high MgO (7.84-14.1 wt%), K2O (3.94-5.07 wt%) and TiO2 (2.69-3.23 wt%) contents, low SiO2 (41.3-45.7 wt%), Na2O (0.21-0.28 wt%) and Al2O3 (6.10-7.20 wt%) contents. All lamproites have elevated Cr (452-599 ppm) and Ni (485-549 ppm) abundances, as well as high Ba (1884-3589 ppm), La (160-186 ppm), Sr (898-1152 ppm) and Zr (532-632 ppm) concentrations. They show uniform REE distribution patterns that are strongly enriched in light REEs relative to heavy REEs [(La/Yb)N?=?71.1-87.6], and exhibit OIB-like geochemical features with obvious enrichment of both LILEs and HFSEs in the primitive mantle-normalized multi-element distribution diagram. Moderately radiogenic Sr (87Sr/86Sri?=?0.706336-0.707439), unradiogenic Nd (143Nd/144Ndi?=?0.511687-0.511704 and ?Nd(t)?=????12.2 to???11.9), and low initial Pb (206Pb/204Pbi?=?16.80-16.90, 207Pb/204Pbi?=?15.34-15.35 and 208Pb/204Pbi?=?37.43-37.70) isotopic compositions are obtained from the rocks. They yield old model ages of TDM(Nd)?=?1.48-1.54 Ga. These signatures suggest that the Baifen lamproite magmas are alkaline, ultrapotassic and ultramafic in character and mainly represent mantle-derived primary melts, which have undergone insignificant crustal contamination and negligible fractional crystallization. The Baifen lamproites originated from a veined metasomatized lithospheric mantle source. We envisage that they were derived by partial melting of old, mineralogically complex metasomatic vein assemblages in the subcontinental lithospheric mantle beneath the southern Yangtze Block. The source region experienced ancient mantle metasomatism with complex modification by enriched fluids and melts. The metasomatic agents are most likely to originate from pre-existing slab subduction beneath the southeastern margin of the Yangtze Block. Tectonically, the Baifen lamproites were emplaced at the southern margin of the Yangtze Block, and they formed in an intraplate extensional setting, showing an anorogenic affinity. In terms of time and space, the genesis of Baifen lamproites is presumably related to the Emeishan large igneous province. The Emeishan mantle plume is suggested as an effective mechanism for rapid extension and thinning of the lithosphere, followed by decompression melting of the subcontinental lithospheric mantle. Combined with the thermal perturbation from asthenospheric upwelling induced by the Emeishan mantle plume, the lamproite magmas, representing small volume and limited partial melts of ancient enriched mantle lithosphere, arose. We propose that the generation of the Baifen lamproite dikes probably was a consequence of the far-field effects of the Emeishan mantle plume.
DS202003-0371
2020
Xie, L. , Yoneda, A., Andraught, D.Formation of bridgmanite-enriched layer at the top lower-mantle during magma ocean solificiation.Nature Communications, Vol. 11, pp. 1-10.Mantlebridgmanite

Abstract: Thermochemical heterogeneities detected today in the Earth’s mantle could arise from ongoing partial melting in different mantle regions. A major open question, however, is the level of chemical stratification inherited from an early magma-ocean (MO) solidification. Here we show that the MO crystallized homogeneously in the deep mantle, but with chemical fractionation at depths around 1000?km and in the upper mantle. Our arguments are based on accurate measurements of the viscosity of melts with forsterite, enstatite and diopside compositions up to ~30?GPa and more than 3000?K at synchrotron X-ray facilities. Fractional solidification would induce the formation of a bridgmanite-enriched layer at ~1000?km depth. This layer may have resisted to mantle mixing by convection and cause the reported viscosity peak and anomalous dynamic impedance. On the other hand, fractional solidification in the upper mantle would have favored the formation of the first crust.
DS202006-0957
2016
Xie, Y., Hou, Z., Goldfarb, R.J., Guo, X., Wang, L.Rare Earth element deposits in China.SEG Reviews In Economic Geology Chapter 6, Vol. 18, pp. 115-136.ChinaREE

Abstract: China is the world’s leading rare earth element (REE) producer and hosts a variety of deposit types. Carbonatite- related REE deposits, the most significant deposit type, include two giant deposits presently being mined in China, Bayan Obo and Maoniuping, the first and third largest deposits of this type in the world, respectively. The carbonatite-related deposits host the majority of China’s REE resource and are the primary supplier of the world’s light REE. The REE-bearing clay deposits, or ion adsorption-type deposits, are second in importance and are the main source in China for heavy REE resources. Other REE resources include those within monazite or xenotime placers, beach placers, alkaline granites, pegmatites, and hydrothermal veins, as well as some additional deposit types in which REE are recovered as by-products. Carbonatite-related REE deposits in China occur along craton margins, both in rifts (e.g., Bayan Obo) and in reactivated transpressional margins (e.g., Maoniuping). They comprise those along the northern, eastern, and southern margins of the North China block, and along the western margin of the Yangtze block. Major structural features along the craton margins provide first-order controls for REE-related Proterozoic to Cenozoic carbonatite alkaline complexes; these are emplaced in continental margin rifts or strike-slip faults. The ion adsorption-type REE deposits, mainly situated in the South China block, are genetically linked to the weathering of granite and, less commonly, volcanic rocks and lamprophyres. Indosinian (early Mesozoic) and Yanshanian (late Mesozoic) granites are the most important parent rocks for these REE deposits, although Caledonian (early Paleozoic) granites are also of local importance. The primary REE enrichment is hosted in various mineral phases in the igneous rocks and, during the weathering process, the REE are released and adsorbed by clay minerals in the weathering profile. Currently, these REE-rich clays are primarily mined from open-pit operations in southern China. The complex geologic evolution of China’s Precambrian blocks, particularly the long-term subduction of ocean crust below the North and South China blocks, enabled recycling of REE-rich pelagic sediments into mantle lithosphere. This resulted in the REE-enriched nature of the mantle below the Precambrian cratons, which were reactivated and thus essentially decratonized during various tectonic episodes throughout the Proterozoic and Phanerozoic. Deep fault zones within and along the edges of the blocks, including continental rifts and strike-slip faults, provided pathways for upwelling of mantle material.
DS202006-0958
2019
Xie, Y., Verplanck, P.L., Hou, Z., Zhong, R.Rare Earth element deposits in China: a review and new understandings.SEG Special Publication , No. 22, pp. 500-552.ChinaREE

Abstract: The rare earth elements (REEs) consist of the 15 lantha-nide elements (La to Lu). Because of the increasing application of REEs and yttrium (REY) in high-and green-tech industries, the demand for the REY is projected to increase in the future. Rare earth elements are relatively abundant in the Earth's crust, but discovered, minable concentrations are less common than for most other ore types. Bastnaesite and monazite are the main mineral source of REEs in the world. Bastnaesite-hosted deposits in China and the United States Abstract China has been the world's leading rare earth element (REE) and yttrium producer for more than 20 years and hosts a variety of deposit types. Carbonatite-related REE deposits are the most significant REE deposit type, with REY (REE and yttrium)-bearing clay deposits, or ion adsorption-type deposits, being the primary source of the world's heavy REEs. Other REY resources in China include those hosted in placers, alkaline granites, pegmatites, and hydrothermal veins, as well as in additional deposit types in which REEs may be recovered as by-product commodities. Carbonatite-related REE deposits in China provide nearly all the light REE production in the world. Two giant deposits are currently being mined in China: Bayan Obo and Maoniuping. The carbonatite-related REE deposits in China occur along the margins of Archean-Paleoproterozoic blocks, including the northern , southern, and eastern margins of the North China craton, and the western margin of the Yangtze craton. The carbonatites were emplaced in continental rifts (e.g., Bayan Obo) or translithospheric strike-slip faults (e.g., Maoniuping) along reactivated craton margins. The craton margins provide the first-order control for carbonatite-related REE resources. Four REE metallogenic belts, including the Proterozoic Langshan-Bayan Obo, late Paleozoic-early Mesozoic eastern Qinling-Dabie, late Mesozoic Chishan-Laiwu-Zibo, and Cenozoic Mianning-Dechang belts, occur along cratonic margins. Geologic and geochemical data demonstrate that the carbonatites in these belts originated from mantle sources that had been previously enriched, most likely by recycled marine sediments through subduction zones during the assembly of continental blocks. Although the generation of carbonatite magma is debated, a plausible mechanism is by liquid immiscibility between silicate and carbonate melts. This process would further enrich REEs in the carbonatite end member during the evolution of mantle-derived magma. The emplacement of carbonatite magma in the upper crust, channeled by translithospheric faults in extensional environments, leads to a rapid decompression of the magma and consequently exsolution of a hydrothermal fluid phase. The fluid is characterized by high temperature (600°-850°C), high pressure (up to 350 MPa), and enrichment in sulfate, CO2, K, Na, Ca, Sr, Ba, and REEs. Immiscibility of sulfate melts from the aqueous fluid, and phase separation between CO2 and water may take place upon fluid cooling. Although both sulfate and chloride have been called upon as important ligands in hydrothermal REE transport, results of our studies suggest that sulfate is more important. The exsolution of a sulfate melt from the primary carbonatite fluid would lead to a significant decrease of the sulfate activity in the fluid and trigger REE precipitation. The subsequent unmixing between CO2 and water may also play an important role in REE precipitation. Because of the substantial ability of the primary carbonatite fluid to contain REEs, a large-volume magma chamber or huge fluid flux are not necessary for the formation of a giant REE deposit. A dense carbonatite fluid and rapid evolution hinder long distance fluid transportation and distal mineralization. Thus, carbonatite-related alteration and mineralization occur in or proximal to carbonatite dikes and sills, and this is observed in all carbonatite-related REE deposits in China. Ion adsorption-type REE deposits are primarily located in the South China block and are genetically linked to the weathering of granite and, less commonly, volcanic rocks and lamprophyres. Indosinian (early Mesozoic) and Yanshanian (late Mesozoic) granites are the most important parent rocks for these REE deposits. Hydro-thermal alteration by fluids exsolved from late Mesozoic granites or related alkaline rocks (e.g., syenite) may have enriched the parent rocks in REEs, particularly the heavy REEs. Furthermore, this alteration process led to the transformation of some primary REE minerals to secondary REE minerals that are more readily broken down during subsequent weathering. During the weathering process, the REEs are released from parent rocks and adsorbed onto kaolinite and halloysite in the weathering profile, and further enriched by the loss of other material to form the ion adsorption-type REE deposits. A warm and humid climate and a low-relief landscape are important characteristics for development of ion adsorption REE deposits.
DS202011-2069
2019
Xie, Y., Verplank, P.L., Hou, Z., Zhong, R.IN: An overview of mineral deposits of China. Rare earth element deposits in China.SEG Special Publication, No. 22, pp. 509-552.ChinaREE

Abstract: China is the world’s leading rare earth element (REE) producer and hosts a variety of deposit types. Carbonatite- related REE deposits, the most significant deposit type, include two giant deposits presently being mined in China, Bayan Obo and Maoniuping, the first and third largest deposits of this type in the world, respectively. The carbonatite-related deposits host the majority of China’s REE resource and are the primary supplier of the world’s light REE. The REE-bearing clay deposits, or ion adsorption-type deposits, are second in importance and are the main source in China for heavy REE resources. Other REE resources include those within monazite or xenotime placers, beach placers, alkaline granites, pegmatites, and hydrothermal veins, as well as some additional deposit types in which REE are recovered as by-products. Carbonatite-related REE deposits in China occur along craton margins, both in rifts (e.g., Bayan Obo) and in reactivated transpressional margins (e.g., Maoniuping). They comprise those along the northern, eastern, and southern margins of the North China block, and along the western margin of the Yangtze block. Major structural features along the craton margins provide first-order controls for REE-related Proterozoic to Cenozoic carbonatite alkaline complexes; these are emplaced in continental margin rifts or strike-slip faults. The ion adsorption-type REE deposits, mainly situated in the South China block, are genetically linked to the weathering of granite and, less commonly, volcanic rocks and lamprophyres. Indosinian (early Mesozoic) and Yanshanian (late Mesozoic) granites are the most important parent rocks for these REE deposits, although Caledonian (early Paleozoic) granites are also of local importance. The primary REE enrichment is hosted in various mineral phases in the igneous rocks and, during the weathering process, the REE are released and adsorbed by clay minerals in the weathering profile. Currently, these REE-rich clays are primarily mined from open-pit operations in southern China. The complex geologic evolution of China’s Precambrian blocks, particularly the long-term subduction of ocean crust below the North and South China blocks, enabled recycling of REE-rich pelagic sediments into mantle lithosphere. This resulted in the REE-enriched nature of the mantle below the Precambrian cratons, which were reactivated and thus essentially decratonized during various tectonic episodes throughout the Proterozoic and Phanerozoic. Deep fault zones within and along the edges of the blocks, including continental rifts and strike-slip faults, provided pathways for upwelling of mantle material.
DS202007-1185
2020
Xu, R., Liu, Y., Lambert, S.Melting of a hydrous peridotite mantle source under the Emeishan large igneous province.Earth Science Reviews, in press available 30p. PdfChinapicrites

Abstract: Large igneous provinces on Earth result from anomalously enormous volcanic eruptions at high melt production rates. These eruptions are often linked to catastrophic events such as mass extinctions, global climate changes, or continental break-up. Decoding their petrogenesis is therefore of great importance for our comprehensive understanding of the evolution and geodynamics of our planet. The ~260 Ma Emeishan large igneous province is an important geological feature of SW China with world-class ore deposits and is also suggested to be linked with the Capitanian mass extinction. However, fundamental aspects of the genesis of Emeishan province's most primitive lavas (picrites), such as the source lithology (pyroxenite or peridotite), the origin of compositional variations of olivines and the melting temperature and pressure conditions, remain poorly constrained. Here, we compile information on melt inclusion and host olivine, and whole-rock compositions from the ELIP picrites and show that these data are consistent with decompression melting of a relatively homogeneous peridotitic mantle plume, with a potential temperature higher than 1560 °C. The compositional variability of the olivines and picrites can be explained by varying the equilibrium depth of primary magma segregation and does not require the contribution of a pyroxenite component as previously suggested. Our results favor a scenario for the origin of the Emeishan large igneous province in which the decompression melting during upwelling of a hot hydrous and oxidized mantle plume is accompanied by catastrophic lithospheric thinning. In combination with the now extensive multi-element geochemical data, our findings provide a starting point for re-evaluation of the petrogenesis models for large igneous provinces.
DS202002-0220
2019
Xu, R., Liu, Y., Wang, X-C, Foley, S.F., Zhang, Y., Yuan, H.Generation of continental intraplate alkali basalts and deep carbon cycle.Earth Science Reviews, in press available, 38p. Doi.org/1010.1016 /jearsciev.2019.103073Globalcarbon

Abstract: Although the deep recycling of carbon has been proposed to play a key role in producing intraplate magmatism, the question of how it controls or triggers mantle melting remains poorly understood. In addition, generation of incipient carbonated melts in the mantle and their subsequent reaction with the mantle are critical processes that can influence the geochemistry of intraplate basalts, but the details of such processes are also unclear. Here we present geochemical evidence for the existence of pervasive carbonate melt in the mantle source of Cenozoic continental intraplate highly alkali basalts (SiO2 < 45 wt%), which are volumetrically minor but widespread in eastern China. The primary magma compositions of these basalts cannot be explained by either partial melting of a single mantle source lithology or mixing of magmas derived from distinct mantle sources, but can be adequately explained by carbonate-fluxed melting of eclogite and subsequent reaction between silica-rich melts and peridotite that ultimately transformed the initial carbonated silica-rich melts into silica-undersaturated alkalic magmas. The source of the carbonate is in subducted eclogites associated with the Pacific plate, which stagnated in the mantle transition zone (MTZ). The spatial distribution of the alkali basalts is in accord with large-scale seismic low-velocity anomalies in the upper mantle above the MTZ. Similar scenarios in central-western Europe and eastern Australia lead us to propose that reaction between carbonated silica-rich melt and peridotite may be a pivotal mechanism for the generation of continental intraplate alkali basalts elsewhere in the world.
DS202008-1458
2020
Xue, S., Ling, M-X., Liu, Y-L., Kang, Q-Q., Huang, R-F., Zhang, Z-K., Sun, W.The formation of the giant Huayangchuan U-Nb deposit associated with carbonatite in the Qinqling orogenic belt.Ore Geology Reviews, Vol. 122, 103498, 16p. PdfChinacarbonatite

Abstract: Carbonatitic magmatism plays a significant role in outgassing carbon from mantle and the formation of rare earth element (REE), rare metal (e.g., Nb and Th) and other types of deposits. The mechanism of REE mineralization associated with carbonatite have been widely studied. However, it is hard to understand U-Nb mineralization without Th enrichment associated with carbonatite. Here we report a carbonatite-hosted U-Nb deposit in Huayangchuan, located in the north Qinling Orogenic Belt. Field observation, mineralogy and geochemical analysis on a suite of drillhole samples were conducted to decipher the mineralization mechanism and its relationship with carbonatite. Huayangchuan carbonatite samples mainly consist of calcite and augite with small volume of accessory minerals (e.g., allanite, fluorapatite, barite and celestite). Betafite [(Ca,U)2(Ti,Nb,Ta)2O6(OH)] is the major ore-bearing mineral in Huayangchuan deposit. The carbonatite shows high CaO, low MgO and alkali contents, which should be products to be differentiated from primary carbonatite (high MgO and alkali contents). The immiscibility and crystallization processes could explain the high CaO/(CaO + MgO + FeO) ratios and the enrichment of LILE. Numerical modeling also indicates positive ?18OSMOW (7.29 to 15.53‰) and negative ?13CPDB (?5.26 to ?10.08‰) shifts are induced by reduced sediments assimilation from source consistent with there being enriched Sr-Nd and low Mg isotopic compositions. LA-ICP-MS zircon U-Pb dating of Huayangchuan carbonatite yielded Triassic ages of 229 ± 3 Ma, which corresponds to the post-collision stage of Qinling Orogen during the middle-late Triassic. We then proposed that the recycling of subducted sediments and later re-melting of those materials in shallow mantle generated the Huayangchuan carbonatite and subsequently formed the Huayangchuan deposit. Fluorine concentration decrease, caused by fluorapatite crystallization, ultimately resulted in betafite mineralization.
DS202009-1675
2020
Yakovlev, E.Yu.Features of radioactive element distribution within the Arkhangelsk diamondiferous province: possible directions for development of isotope-radiogeochemical methods for kimberlite prospecting in complex landscape geology and climate conditions of the subaGeochemistry: Exploration, Environment, Analysis, Vol. 20, pp. 269-279. pdfRussia, Arkangelgeochemisty
DS202004-0547
2020
Yan, J., Ballmer, M.D., Tackley, P.J.The evolution and distribution of recycled oceanic crust in the Earth's mantle: insight from geodynamic models.Earth and Planetary Science Letters, Vol. 537, 116171 12p. PdfMantlegeothermometry

Abstract: A better understanding of the Earth's compositional structure is needed to place the geochemical record of surface rocks into the context of Earth accretion and evolution. Cosmochemical constraints imply that lower-mantle rocks may be enriched in silica relative to upper-mantle pyrolite, whereas geophysical observations support whole-mantle convection and mixing. To resolve this discrepancy, it has been suggested that subducted mid-ocean ridge basalt (MORB) segregates from subducted harzburgite to accumulate in the mantle transition zone (MTZ) and/or the lower mantle. However, the key parameters that control basalt segregation and accumulation remain poorly constrained. Here, we use global-scale 2D thermochemical convection models to investigate the influence of mantle-viscosity profile, planetary-tectonic style and bulk composition on the evolution and distribution of mantle heterogeneity. Our models robustly predict that, for all cases with Earth-like tectonics, a basalt-enriched reservoir is formed in the MTZ, and a harzburgite-enriched reservoir is sustained at 660?800 km depth, despite ongoing whole-mantle circulation. The enhancement of basalt and harzburgite in and beneath the MTZ, respectively, are laterally variable, ranging from ?30% to 50% basalt fraction, and from ?40% to 80% harzburgite enrichment relative to pyrolite. Models also predict an accumulation of basalt near the core mantle boundary (CMB) as thermochemical piles, as well as moderate enhancement of most of the lower mantle by basalt. While the accumulation of basalt in the MTZ does not strongly depend on the mantle-viscosity profile (explained by a balance between basalt delivery by plumes and removal by slabs at the given MTZ capacity), that of the lowermost mantle does: lower-mantle viscosity directly controls the efficiency of basalt segregation (and entrainment) near the CMB; upper-mantle viscosity has an indirect effect through controlling slab thickness. Finally, the composition of the bulk-silicate Earth may be shifted relative to that of upper-mantle pyrolite, if indeed significant reservoirs of basalt exist in the MTZ and lower mantle.
DS202005-0772
2020
Yan, J., Ballmer, M.D., Tackley, P.J.The evolutiom and distribution of recycled oceanic crust in the Earth's mantle: insight from geodynamic models. ( harzburgite)Earth and Planetary Science Letters, Vol. 537, 116171, 12p. PdfMantlegeodynamics

Abstract: A better understanding of the Earth's compositional structure is needed to place the geochemical record of surface rocks into the context of Earth accretion and evolution. Cosmochemical constraints imply that lower-mantle rocks may be enriched in silica relative to upper-mantle pyrolite, whereas geophysical observations support whole-mantle convection and mixing. To resolve this discrepancy, it has been suggested that subducted mid-ocean ridge basalt (MORB) segregates from subducted harzburgite to accumulate in the mantle transition zone (MTZ) and/or the lower mantle. However, the key parameters that control basalt segregation and accumulation remain poorly constrained. Here, we use global-scale 2D thermochemical convection models to investigate the influence of mantle-viscosity profile, planetary-tectonic style and bulk composition on the evolution and distribution of mantle heterogeneity. Our models robustly predict that, for all cases with Earth-like tectonics, a basalt-enriched reservoir is formed in the MTZ, and a harzburgite-enriched reservoir is sustained at 660?800 km depth, despite ongoing whole-mantle circulation. The enhancement of basalt and harzburgite in and beneath the MTZ, respectively, are laterally variable, ranging from ?30% to 50% basalt fraction, and from ?40% to 80% harzburgite enrichment relative to pyrolite. Models also predict an accumulation of basalt near the core mantle boundary (CMB) as thermochemical piles, as well as moderate enhancement of most of the lower mantle by basalt. While the accumulation of basalt in the MTZ does not strongly depend on the mantle-viscosity profile (explained by a balance between basalt delivery by plumes and removal by slabs at the given MTZ capacity), that of the lowermost mantle does: lower-mantle viscosity directly controls the efficiency of basalt segregation (and entrainment) near the CMB; upper-mantle viscosity has an indirect effect through controlling slab thickness. Finally, the composition of the bulk-silicate Earth may be shifted relative to that of upper-mantle pyrolite, if indeed significant reservoirs of basalt exist in the MTZ and lower mantle.
DS202005-0773
2020
Yang, J., Faccenda, M.Intraplate volcanism originating from upwelling hydrous mantle transition zone.Nature, Vol. 579, 7797, pp. 1-4. pdfMantlewater, volcanism

Abstract: Most magmatism occurring on Earth is conventionally attributed to passive mantle upwelling at mid-ocean ridges, to slab devolatilization at subduction zones, or to mantle plumes. However, the widespread Cenozoic intraplate volcanism in northeast China1,2,3 and the young petit-spot volcanoes4,5,6,7 offshore of the Japan Trench cannot readily be associated with any of these mechanisms. In addition, the mantle beneath these types of volcanism is characterized by zones of anomalously low seismic velocity above and below the transition zone8,9,10,11,12 (a mantle level located at depths between 410 and 660 kilometres). A comprehensive interpretation of these phenomena is lacking. Here we show that most (or possibly all) of the intraplate and petit-spot volcanism and low-velocity zones around the Japanese subduction zone can be explained by the Cenozoic interaction of the subducting Pacific slab with a hydrous mantle transition zone. Numerical modelling indicates that 0.2 to 0.3 weight per cent of water dissolved in mantle minerals that are driven out from the transition zone in response to subduction and retreat of a tectonic plate is sufficient to reproduce the observations. This suggests that a critical amount of water may have accumulated in the transition zone around this subduction zone, as well as in others of the Tethyan tectonic belt13 that are characterized by intraplate or petit-spot volcanism and low-velocity zones in the underlying mantle.
DS202003-0372
2020
Yang, J., Simakov, S.K., Moe, K., Scribano, V., Lian, D., Wu, W.Comment on the Comparison of enigmatic diamonds from Tolbachik arc volcano ( Litasov 2019) also Litasov responseGondwana Research, in press availableRussiaKamchatka
DS202006-0959
2020
Yang, J.W., Park, J.H., Byun, M.G., Park, J., Yu, B.D., Hwan, N.M.Beyond carbon solvency effects of catalytic metal Ni on diamond growth.Diamonds & Related Materials, in press available, 27p. PdfGlobalnitrogen

Abstract: To understand the physical and chemical roles of catalytic metal Ni in the growth of diamond, ab-initio calculations of the structural, electronic, and kinetic properties of a Ni-covered C (111) surface were performed. Findings from this theoretical study highlight two important roles of Ni in addition to its carbon-solvency effect, widely known to play a catalytic role in the growth of diamond. The first role is to facilitate the formation of a thermodynamically stable Ni-C interface with a diamond bulk-like structure and the second is to induce surfactant-mediated growth enabling continuous layer-by-layer growth for diamond.
DS202008-1459
2020
Yang, S., Humayaun, M., Salters, V.J.M.Elemental constrains on the amount of recycled crust in the generation of mid-ocean basalts.Science Advances, https://phys.org/ news/2020-06- geochemists- mystery-earth-crust .htmlMantlegeochemistry

Abstract: Mid-oceanic ridge basalts (MORBs) are depleted in incompatible elements, but ridge segments far from mantle plumes frequently erupt chemically enriched MORBs (E-MORBs). Two major explanations of E-MORBs are that these basalts are generated by the melting of entrained recycled crust (pyroxenite) beneath ridges or by the melting of refertilized peridotites. These two hypotheses can be discriminated with compatible element abundances from Sc to Ge, here termed the ScGe elements. Here, we demonstrate that E-MORBs have systematically lower Ge/Si and Sc contents and slightly higher Fe/Mn and Nb/Ta ratios than depleted MORBs (D-MORBs) due to the mixing of low-degree pyroxenite melts. The Ge/Si ratio is a new tracer that effectively discriminates between melts derived from peridotite sources and melts derived from mixed pyroxenite-peridotite sources. These new data are used to estimate the distribution of pyroxenite in the mantle sources of global MORB segments.
DS202001-0050
2020
Yaxley, G.M., Ghosh, S., Kiseeva, E.S., Mallick, A., Spandler, C., Thomson, A.R., Walter, M.J.Co2 rich melts in the earth.IN: Deep Carbon: past to present. Editors Orcutt, Danielle, Dasgupta, pp. 129-162.Mantlemelting

Abstract: This chapter reviews the systematics of partial melting of mantle lithologies - like peridotite and eclogite - in the presence of carbon dioxide. It discusses the composition of mantle-derived magmas generated in the presence of carbon dioxide and whether magmas erupted on Earth’s surface resemble carbonated magmas from the mantle. It reviews how the production of carbon dioxide-rich magma in the mantle varies as a function of tectonic settings - beneath continents and oceans and in subduction zones - and time.
DS202002-0221
2020
Yelisseyev, A., Gromilov, S., Afanasiev, V., Sildos, I., Kiisk, V.Effect of lonsdaleite on the optical properties of impact diamonds.Diamonds & Related Materials, Vol. 101, 107640, 13p. PdfRussiaPopigai

Abstract: The special features of impact diamonds are the orientation of the nanosized grains relative to each other, the presence of hexagonal diamond (lonsdaleite, L) in a large part of the samples and the increased wear resistance. Using Raman spectroscopy and XRD, two groups of translucent samples of Popigai impact diamonds (PIDs) were selected: with and without lonsdaleite and the effect of lonsdaleite on the optical properties of the samples was studied. In all L-containing PIDs there is a strong absorption band of about 1230 cm-1 in the one-phonon region, in the mid-IR. The absorption edge is blurred and described by the Urbach rule. The estimated value of Eg ~4 eV for L is consistent with the first principles calculations. Impurity nitrogen is found only in L-free PIDs: There are signals from nitrogen-vacancy complexes in the photoluminescence (PL) spectra. Variations in the number of nitrogen atoms (N = 1 to 4) in the structure of these centers indicate significant variations in the parameters of PID annealing. L-containing PIDs are characterized by large strains in the lattice and, as a consequence, there are problems with the defect diffusion. The narrow lines in PL spectra, uncommon for diamond, can be the result of several orders of magnitude higher concentrations of impurities in PIDs formed during the solid-phase transition. The broadened peaks of 180, 278 and 383 K are distinguishable in the curves of thermostimulated luminescence (TSL) for L-free PIDs, but in the presence of L the TSL glow becomes continuous as in natural IaA-type diamonds with platelets. In general, lonsdaleite deteriorates the optical properties of impact diamonds and makes it difficult to create certain types of impurity-vacancy complexes for different applications.
DS202003-0373
2020
Yin, A., Brandl, G., Kroner, A.Plate tectonics processes at ca 2.0 Ga: evidence from >600 km of plate convergence. Limpopo beltGeology, Vol. 48, pp. 103-107.Africa, South Africatectonics

Abstract: We addressed when plate-tectonic processes first started on Earth by examining the ca. 2.0 Ga Limpopo orogenic belt in southern Africa. We show through palinspastic reconstruction that the Limpopo orogen originated from >600 km of west-directed thrusting, and the thrust sheet was subsequently folded by north-south compression. The common 2.7-2.6 Ga felsic plutons in the Limpopo thrust sheet and the absence of an arc immediately predating the 2.0 Ga Limpopo thrusting require the Limpopo belt to be an intracontinental structure. The similar duration (?40 m.y.), slip magnitude (>600 km), slip rate (>15 mm/yr), tectonic setting (intracontinental), and widespread anatexis to those of the Himalayan orogen lead us to propose the Limpopo belt to have developed by continent-continent collision. Specifically, the combined Zimbabwe-Kaapvaal craton (ZKC, named in this study) in the west (present coordinates) was subducting eastward below an outboard craton (OC), which carried an arc equivalent to the Gangdese batholith in southern Tibet prior to the India-Asia collision. The ZKC-OC collision at ca. 2.0 Ga triggered a westward jump in the plate convergence boundary, from the initial suture zone to the Limpopo thrust within the ZKC. Subsequent thrusting accommodated >600 km of plate convergence, possibly driven by ridge push from the west side of the ZKC. As intracontinental plate convergence is a key modern plate-tectonic process, the development of the Limpopo belt implies that the operation of plate tectonics, at least at a local scale, was ongoing by ca. 2.0 Ga on Earth.
DS202006-0960
2020
Ying, Y-C., Chen, W., Simonetti, A., Jiang, S-Y., Zhao, K-D.Significance of hydrothermal reworking for REE mineralization associated with carbonatite: constraints from in situ trace element and C-Sr isotope study of calcite and apatite from the Miaoya carbonatite complex (China).Geochimica et Cosmochimica Acta, in press available 45p. PdfChinadeposit - Miaoya

Abstract: A majority of carbonatite-related rare earth element (REE) deposits are found in cratonic margins and orogenic belts, and metasomatic/hydrothermal reworking is common in these deposits; however, the role of metasomatic processes involved in their formation remains unclear. Here, we present a comprehensive in situ chemical and isotopic (C-Sr) investigation of calcite and fluorapatite within the Miaoya carbonatite complex located in the South Qinling orogenic belt, with the aim to better define the role of late-stage metasomatic processes. Carbonatite at Miaoya commonly occurs as stocks and dykes intruded into associated syenite, and can be subdivided into equigranular (Type I) and inequigranular (Type II) calcite carbonatites. Calcite in Type I carbonatite is characterized by the highest Sr (up to ?22,000?ppm) and REE (195-542?ppm) concentrations with slight LREE-enriched chondrite normalized patterns [(La/Yb)N?=?2.1-5.2]. In situ C and Sr isotopic compositions of calcite in Type I carbonatite define a limited range (87Sr/86Sr?=?0.70344-0.70365; ?13C?=??7.1 to ?4.2 ‰) that are consistent with a mantle origin. Calcite in Type II carbonatite has lower Sr (1708-16322?ppm) and REEs (67-311?ppm) and displays variable LREE-depleted chondrite normalized REE patterns [(La/Yb)N?=?0.2-3.3; (La/Sm)N?=?0.2-2.0]. In situ 87Sr/86Sr and d13C isotopic compositions of Type II calcite are highly variable and range from 0.70350 to 0.70524 and ?7.0 to ?2.2 ‰, respectively. Fluorapatite in Type I and Type II carbonatites is characterized by similar trace-element and isotopic compositions. Both types of fluorapatite display variable trace element concentrations, especially LREE contents, whereas they exhibit relatively consistent near-chondritic Y/Ho ratios. Fluorapatite is characterized by consistent Sr isotopic compositions with a corresponding average 87Sr/86Sr ratio of 0.70359, which suggests that fluorapatite remained relatively closed in relation to contamination. The combined geochemical and isotopic data for calcite and fluorapatite from the Miaoya complex suggest that carbonatite-exsolved fluids together with possible syenite assimilation during the Mesozoic metasomatism overprinted the original trace-element and isotopic signatures acquired in the early Paleozoic magmatism. Hydrothermal reworking resulted in dissolution-reprecipitation of calcite and fluorapatite, which served as the dominant source of REE mineralization during the much younger metasomatic activity. The results from this study also suggest that carbonatites located in orogenic belts and cratonic edges possess a great potential for forming economic REE deposits, especially those that have undergone late-stage metasomatic reworking.
DS202007-1186
2020
Yoshida, M., Saito, S., Yoshozawa, K.Possible tectonic patterns along the eastern margin of Gondwanaland from numerical studies of mantle convection.Tectonophysics, Vol. 787, 228476, 12p. PdfMantleconvection

Abstract: Two end-member scenarios have been proposed for the tectonic situation along the eastern margins of Gondwanaland before Zealandia was formed ca. 100 million years ago (Ma), namely: (1) A subduction zone located far from the eastern margin of Zealandia, wherein Zealandia may have separated from Gondwanaland by plume push of an active hotspot plume.; (2) A subduction zone located along the eastern margin of Gondwanaland, wherein Zealandia possibly separated from Gondwanaland via trench/subduction retreat. Assuming that the thermal structure of the deep mantle and source of hotspot plumes remained relatively stationary over the last hundred million years, major hotspot plumes with a large buoyancy flux did not exist under Zealandia; the eastern margins of Gondwanaland were far from two large low-shear-velocity provinces under the Africa-Atlantic and South Pacific regions. Herein, through numerical studies of three-dimensional global mantle convection, we examined the mantle convection and surface tectonic patterns at ~100 Ma. The present model considered the real configuration of Gondwanaland at the model surface to observe long-term variations of mantle convection and the resulting surface tectonic conditions. The results demonstrate that the extensive subduction zones developed preferentially along the eastern margin of Gondwanaland when the temperature anomaly of the lower mantle was primarily dominated by high-temperature regions under present-day Africa-Atlantic and South Pacific regions. The results of this study support one of the proposed hypotheses, where the breakup at the eastern margins of Gondwanaland at ~100 Ma occurred via trench/subduction retreat.
DS202005-0774
2020
Yuryeva, O.P., Rakhmanova, M.I., Zedgenizov, D.A., Kalinina, V.V.Spectroscopic evidence of the origin of brown and pink diamonds family from Internatsionalnaya kimberlite pipe ( Siberian craton).Physics and Chemistry of Minerals, Vol. 47, 20 doi.org/10/1007/ s00269-020-01088-5 19p. PdfRussiadeposit - International

Abstract: New spectroscopic data were obtained to distinguish the specific features of brown and pink diamonds from Internatsionalnaya kimberlite pipe (Siberian craton). It is shown that pink and brown samples differ markedly in the content and degree of aggregation of nitrogen defects. Pink diamonds generally have higher nitrogen content and a lower aggregation state compared to brown samples, which often show significant variations in nitrogen content and aggregation state between different growth zones. The 491 and 576 nm luminescent centres, which are signs of deformed brown diamonds, are absent or of low intensity in pink diamonds implying that high nitrogen content predominantly in A form in the pink diamonds had stiffened the diamonds against natural plastic deformation. The GR1 centre, formed by a neutrally charged vacancy, was observed only in pink diamonds, which may be due to their formation and storage in the mantle at lower-temperature conditions. Mineral inclusions indicate peridotitic and eclogitic paragenesis for studied brown and pink diamonds, respectively. It is suggested that brown diamonds have been formed in a primitive mantle at higher temperatures and/or stored there much longer.
DS202004-0548
2020
Zaitsev, A., Kazuchits, N.M., Kazuchits, V.N., Wang, W.Nitrogen doped CVD diamond: nitrogen concentration, color and internal stress.Diamond and Related Materials, March Globalsynthetics

Abstract: Single crystal CVD diamond has been grown on (100)-oriented CVD diamond seed in six layers to a total thickness of 4.3 mm, each layer being grown in gas with increasing concentration of nitrogen. The nitrogen doping efficiency, distribution of color and internal stress have been studied by SIMS, optical absorption, Raman spectroscopy and birefringence imaging. It is shown that nitrogen doping is very non-uniform. This non-uniformity is explained by the terraced growth of CVD diamond. The color of the nitrogen-doped diamond is grayish-brown with color intensity gradually increasing with nitrogen concentration. The absorption spectra are analyzed in terms of two continua representing brown and gray color components. The brown absorption continuum exponentially rises towards short wavelength. Its intensity correlates with the concentration of nitrogen C-defects. Small vacancy clusters are discussed as the defects responsible for the brown absorption continuum. The gray absorption continuum has weak and almost linear spectral dependence through the near infrared and visible spectral range. It is ascribed to carbon nanoclusters which may form in plasma and get trapped into growing diamond. It is suggested that Mie light scattering on the carbon nanoclusters substantially contributes to the gray absorption continuum and determines its weak spectral dependence. A Raman line at a wavenumber of 1550 cm?1 is described as a characteristic feature of the carbon nanoclusters. The striation pattern of brown/gray color follows the pattern of anomalous birefringence suggesting that the vacancy clusters and carbon inclusions are the main cause of internal stress in CVD diamond. A conclusion is made that high perfection of seed surface at microscale is not a required condition for growth of low-stress, low-inclusion single crystal CVD diamond. Crystallographic order at macroscale is more important requirement for the seed surface.
DS202006-0961
2020
Zaitsev, A.M., Kazuchits, N.M., Kazuchits, V.N., Moe, K.S., Rusetsky, M.S., Korolik, O.V., Kitajima, K., Butler, J.E., Wang, W.Nitrogen-doped CVD diamond: nitrogen concentration, color and internal stress.Diamonds & Related Materials, Vol. 105, 13p. pdfMantlenitrogen

Abstract: Single crystal CVD diamond has been grown on (100)-oriented CVD diamond seed in six layers to a total thickness of 4.3 mm, each layer being grown in gas with increasing concentration of nitrogen. The nitrogen doping efficiency, distribution of color and internal stress have been studied by SIMS, optical absorption, Raman spectroscopy and birefringence imaging. It is shown that nitrogen doping is very non-uniform. This non-uniformity is explained by the terraced growth of CVD diamond. The color of the nitrogen-doped diamond is grayish-brown with color intensity gradually increasing with nitrogen concentration. The absorption spectra are analyzed in terms of two continua representing brown and gray color components. The brown absorption continuum exponentially rises towards short wavelength. Its intensity correlates with the concentration of nitrogen C-defects. Small vacancy clusters are discussed as the defects responsible for the brown absorption continuum. The gray absorption continuum has weak and almost linear spectral dependence through the near infrared and visible spectral range. It is ascribed to carbon nanoclusters which may form in plasma and get trapped into growing diamond. It is suggested that Mie light scattering on the carbon nanoclusters substantially contributes to the gray absorption continuum and determines its weak spectral dependence. A Raman line at a wavenumber of 1550 cm?1 is described as a characteristic feature of the carbon nanoclusters. The striation pattern of brown/gray color follows the pattern of anomalous birefringence suggesting that the vacancy clusters and carbon inclusions are the main cause of internal stress in CVD diamond. A conclusion is made that high perfection of seed surface at microscale is not a required condition for growth of low-stress, low-inclusion single crystal CVD diamond. Crystallographic order at macroscale is more important requirement for the seed surface.
DS202004-0549
2020
Zedgenizov, D., Bogush, I., Shatsky, V., Kovalchuk, O., Ragozin, A., Kalinina, V.Mixed habit type Ib-IaA diamond from an Udachnaya eclogite.Minerals MDPI, Vol. 9, 9120741, 12p. PdfRussiadeposit - Udachnaya

Abstract: The variety of morphology and properties of natural diamonds reflects variations in the conditions of their formation in different mantle environments. This study presents new data on the distribution of impurity centers in diamond type Ib-IaA from xenolith of bimineral eclogite from the Udachnaya kimberlite pipe. The high content of non-aggregated nitrogen C defects in the studied diamonds indicates their formation shortly before the stage of transportation to the surface by the kimberlite melt. The observed sectorial heterogeneity of the distribution of C- and A-defects indicates that aggregation of nitrogen in the octahedral sectors occurs faster than in the cuboid sectors.
DS202008-1460
2020
Zedgenizov, D., Kagi, H., Ohtaini, E., Tsujimori, T., Komatsu, K.Retrograde phases of former bridgemanite inclusions in superdeep diamonds.Lithos, Vol. 370-371, 105659 7p. PdfAfrica, South Africa, Guinea, Australia,South America, Brazil, Canada, Northwest Territoriesdeposit - Koffiefontein, Kankan, Lac de Gras, Juina, Machado, Orroroo

Abstract: (Mg,Fe)SiO3 bridgmanite is the dominant phase in the lower mantle; however no naturally occurring samples had ever been found in terrestrial samples as it undergoes retrograde transformation to a pyroxene-type structure. To identify retrograde phases of former bridgmanite single-phase and composite inclusions of (Mg,Fe)SiO3 in a series of superdeep diamonds have been examined with electron microscopy, electron microprobe, Raman spectroscopy and X-ray diffraction techniques. Our study revealed that (Mg,Fe)SiO3 inclusions are represented by orthopyroxene. Orthopyroxenes in single-phase and composite inclusions inherit initial chemical composition of bridgmanites, including a high Al and low Ni contents. In composite inclusions they coexist with jeffbenite (ex-TAPP) and olivine. The bulk compositions of these composite inclusions are rich in Al, Ti, and Fe, which are similar but not fully resembling Al-rich bridgmanite produced in experiments on the MORB composition. The retrograde origin of composite inclusions due to decomposition of Al-rich bridgmanite may be doubtful because each of observed minerals may represent coexisting HP phases, i.e. bridgmanite or ringwoodite.
DS202007-1187
2020
Zedgenizov, D., Kagi, H., Ohtani, E., Tsujimori, T., Komatsu, K.Retrograde phases of former bridgemanite inclusions in superdeep diamonds.Lithos, in press available, 25p. PdfSouth America, Brazil, Africa, South Africa, Guinea, Canada, Northwest Territoriesdeposit - Sao Luis, Juina

Abstract: Bridgmanite (Mg,Fe)SiO3, a high pressure silicate with a perovskite structure, is dominant material in the lower mantle at the depths from 660 to 2700 km and therefore is probably the most abundant mineral in the Earth. Although synthetic analogues of this mineral have been well studied, no naturally occurring samples had ever been found in a rock on the planet’s surface except in some shocked meteorites. Due to its unstable nature under ambient conditions, this phase undergoes retrograde transformation to a pyroxene-type structure. The identification of the retrograde phase as ‘bridgmanite’ in so-called superdeep diamonds was based on the association with ferropericlase (Mg,Fe)O and other high-pressure (supposedly lower-mantle) minerals predicted from theoretical models and HP-HT experiments. In this study pyroxene inclusions in diamond grains from Juina (Brazil), one single-phase (Sample SL-14) and two composite inclusions of (Mg,Fe)SiO3 coexisting with (Mg,Fe)3Al2Si3O12 (Sample SL-13), and with (Mg,Fe)3Al2Si3O12 and (Mg,Fe)2SiO4 (Sample SL-80) have been analyzed to identify retrograde phases of former bridgmanite. XRD and Raman spectroscopy have revealed that these are orthopyroxene (Opx). (Mg,Fe)2SiO4 and (Mg,Fe)3Al2Si3O12 in these inclusions are identified as olivine and jeffbenite (TAPP). These inclusions are associated with inclusions of (Mg,Fe)O (SL-14), CaSiO3 (SL-80) and composite inclusion of CaSiO3+CaTiO3 (SL-13). XRD patterns of (Mg,Fe)SiO3 inclusions indicate that they consist of polycrystals. This polycrystalline textures together with high lattice strain of host diamond around these inclusions observed from EBSD may be an evidence for the retrograde phase transition of former bridgmanite. Single-phase inclusions of (Mg,Fe)SiO3 in superdeep diamonds are suggested to represent a retrograde phase of bridgmanite and fully inherit its initial chemical composition, including a high Al and low Ni contents [Harte, Hudson, 2013; Kaminsky, 2017]. The composite inclusions of (Mg,Fe)SiO3 with jeffbenite and other silicate and oxide phases may be interpreted as exolusion products from originally homogeneous bridgmanite [Walter et al., 2011]. The bulk compositions of these composite inclusions are rich in Al, Ti, and Fe which are similar to Al-rich bridgmanite produced in experiments on the MORB composition. However, the retrograde origin of composite inclusions due to decomposition of Al-rich bridgmanite may be doubtful because each of observed phases may represent single-phase inclusions, i.e. bridgmanite and high pressure garnet (majoritic garnet), with similar compositional features.
DS202012-2256
2020
Zedgenizov, D.A., Skuzovatov, S.Y., Griffin, W.L., Pomazansky, B.S., Ragozin, A.:., Kalinina, V.V.Diamond forming HDFs tracking episodic mantle metasomatism beneath Nyurbinskaya kimberlite pipe (Siberian craton).Contributions to Mineralogy and Petrology, Vol. 175, 106, 21p. PdfRussiadeposit - Nyurbinskaya

Abstract: We present a new dataset on the composition of high-density fluids (HDFs) in cloudy (n?=?25), coated (n?=?10) and cuboid (n?=?10) diamonds from the Nyurbinskaya kimberlite pipe. These diamonds represent different populations each showing distinct growth histories. The cores of coated diamonds display multiple growth stages and contrasting sources of carbon. Fibrous coats and cuboid diamonds have similar carbon isotopes and nitrogen systematics, suggesting their formation in the last metasomatic events related to kimberlite magmatism, as is common for most such diamonds worldwide. The HDFs in most of these diamonds span a wide range from low-Mg carbonatitic to hydrous silicic compositions. The major- and trace-element variations suggest that the sources for such HDFs range in composition between the depleted mantle and more fertile mantle reservoirs. Hydrous-silicic HDFs could originate from a 13C-enriched source, which originates through subduction of crustal metasedimentary material. Percolation of such HDFs through carbonated eclogites and peridotites facilitates the formation of cuboid diamonds and fibrous coats in the mantle section beneath the corresponding area of the Siberian craton. Cloudy diamonds represent an apparently older population, reflecting continuous diamond formation predominantly from high-Mg carbonatitic HDFs that caused discrete episodes of diamond precipitation. Their high Mg# and enrichment in incompatible elements support a metasomatized peridotitic source for these HDFs.
DS202011-2070
2020
Zemnukhov, A.L., Reutsky, V.N., Zedgenizov, D.A., Ragozin, A.L., Zhelonkin, R.Y., Kalinina, V.V.Subduction related population of diamonds in Yakutian placers, northeastern Siberian platform.Contributions to Mineralogy and Petrology, Vol. 175, 98 10.1007/s00410-020-01741-w 11p. PdfRussia, Yakutiadiamond crystallography

Abstract: The 35 paired diamond intergrowths of rounded colorless transparent and gray opaque crystals from the placers of northeastern Siberian Platform were investigated. Mineral inclusions (KFsp, Coe, E-Grt, Po) detected in studied samples belong to eclogitic paragenesis. The majority of studied samples have uniform ranges of nitrogen content (1126-1982 at. ppm) and carbon isotope composition (??16.8 to ??23.2 ‰). These characteristics pointing towards subducted material are possible sources for their genesis. Two samples consist of a gray opaque crystal with the subduction-related characteristics (?13C ca. ??21‰ and N ca. 1300 at. ppm) and a transparent crystal with low nitrogen content (412 and 29 at. ppm) and a heavy carbon isotopic composition (?13C ??4.2 and ??4.6‰) common for primary mantle range. The higher degree of nitrogen aggregation in the crystals with mantle-like characteristics testifies their longer storage in the mantle conditions. These samples reflect multistage diamond growth history and directly indicate the mixing of mantle and subduction carbon sources at the basement of subcontinental lithospheric mantle of northeastern Siberian Platform.
DS202008-1461
2020
Zeyen, N., Wang, B., Wilson, S.A., von Gunten, K., Alessi, D.S., Paulo, C., Stubbs, A.R., Power, I.M.Cation exchange: a new strategy for mineral carbonation of smectite-rich kimberlites.Goldschmidt 2020, 1p. AbstractAfrica, South Africadeposit - Venetia

Abstract: Mineral carbonation is a form of carbon capture, utilization and storage (CCUS) that aims to transform excess CO2 into environmentally benign carbonate minerals which are geologically stable. Here, we investigated the reactivity of processed kimberlite and kimberlite ore from the Venetia Diamond Mine (South Africa). Highly reactive phases, such as brucite [Mg(OH)2], are uncommon in the samples collected from Venetia necessitating the development of new strategies for mineral carbonation. Kimberlite ore and tailings from this mine consist of a clay-rich mineral assemblage that is dominated by lizardite (a serpentine mineral) and smectites. Smectites are swelling clays that can act as a source of Mg and Ca for carbonation reactions via cation exchange, dissolution and/or direct replacement of smectites to form carbonate phases. Although carbonation of serpentine and brucite has long been a focus of CCUS in mine wastes [1], smectite carbonation has not been explored in this setting. Quantitative X-ray diffraction using Rietveld refinements coupled with Fourier-transform infrared spectroscopy indicate that smectites of stevensite-saponite composition are abundant in the Venetia samples (1.3-15.4 wt.%). Synchrotron-based X-ray fluorescence mapping correlated with scanning and transmission electron microscopy show that smectites are distributed as altered, smooth regions measuring from 1 to 20 ?m in breadth. These phases are rich in Mg and Ca and Al-poor. To better understand the behaviour/reactivity of smectites during the cation exchange process, we have used batch experiments with pure endmembers of Ca-, Mg- and Na-montmorillonite under different treatment conditions (NH4-citrate, NH4-O-acetate, NH4-Cl and Na3-citrate). After 24 hours of reaction, ICP-MS analyses reveal that the four treatments have the same efficiency for Ca and Mg exchange, while NH4-Cl and NH4- O-acetate treatments minimize calcite dissolution. Our end goals are to optimize settling time and to maximize extraction of Ca and Mg for carbonation reactions during ore processing.
DS202005-0775
2020
Zgonnik, V.The occurrence and geoscience of natural hydrogen: a comprehensive review.Earth Science Reviews, Vol. 203, 103140, 51p. PdfGlobalhydrogen

Abstract: Using an interdisciplinary approach, this paper reviews current knowledge in the field of natural hydrogen. For the first time, it combines perspectives on hydrogen from the literature of the former Eastern bloc with that of the West, including rare hardcopies and recent studies. Data are summarized and classified in three main sections: hydrogen as a free gas in different environments, as inclusions in various rock types, and as dissolved gas in ground water. This review conclusively demonstrates that molecular hydrogen is much more widespread in nature than was previously thought. Hydrogen has been detected at high concentrations, often as the major gas, in all types of geologic environment. A critical evaluation of all the proposed mechanisms regarding the origin of natural hydrogen shows that a deep-seated origin is potentially the most likely explanation for its abundance in nature. By combining available data, an estimate of 23 Tg/year for the total annual flow of hydrogen from geologic sources is proposed. This value is an order of magnitude greater than previous estimate but most likely still not large enough to account for recently discovered worldwide diffusive seepages. Hydrogen could play a critical role in mechanisms taking place in both the shallow and deep geospheres and it can influence a very wide range of natural phenomena. Hydrogen is an essential energy source for many microorganisms. Sampling for hydrogen can be a useful tool in studying natural environments, geologic mapping, monitoring of earthquakes, plotting fault traces and resource exploration. Hydrogen of geologic origin has the potential to become the renewable energy source of the future, with exploratory projects ongoing at the present time. The topic of natural hydrogen is therefore relevant from many different perspectives.
DS202001-0051
2018
Zhang, N., Dang, Z., Huang, C., Li, Z-X.The dominant driving force for supercontinent breakup: plume push or subduction retreat?Geoscience Frontiers, Vol. 9, pp. 997-1007.Mantlesubduction

Abstract: Understanding the dominant force responsible for supercontinent breakup is crucial for establishing Earth's geodynamic evolution that includes supercontinent cycles and plate tectonics. Conventionally, two forces have been considered: the push by mantle plumes from the sub-continental mantle which is called the active force for breakup, and the dragging force from oceanic subduction retreat which is called the passive force for breakup. However, the relative importance of these two forces is unclear. Here we model the supercontinent breakup coupled with global mantle convection in order to address this question. Our global model features a spherical harmonic degree-2 structure, which includes a major subduction girdle and two large upwelling (superplume) systems. Based on this global mantle structure, we examine the distribution of extensional stress applied to the supercontinent by both sub-supercontinent mantle upwellings and subduction retreat at the supercontinent peripheral. Our results show that: (1) at the center half of the supercontinent, plume push stress is ?3 times larger than the stress induced by subduction retreat; (2) an average hot anomaly of no higher than 50 K beneath the supercontinent can produce a push force strong enough to cause the initialization of supercontinent breakup; (3) the extensional stress induced by subduction retreat concentrates on a ?600 km wide zone on the boundary of the supercontinent, but has far less impact to the interior of the supercontinent. We therefore conclude that although circum-supercontinent subduction retreat assists supercontinent breakup, sub-supercontinent mantle upwelling is the essential force.
DS202002-0222
2019
Zhang, Y., Nelson, P., Dygert, N., Lin, J-F.Fe alloy slurry and a compacting cumulate pile across Earth's inner-core boundary.Journal of Geophysical Research: Solid Earth, doi:10.1029/ 2019JB017792MantleCore boundary

Abstract: Seismic observations show a reduced P wave velocity gradient layer at the bottom ~280 km of the outer core and a hemispherical dichotomy at the top ~50-200 km of the inner core compared to the one?dimensional Preliminary reference Earth model (PREM). These seismic features manifest physical and chemical phenomena linked to thermal evolution and formation processes of the inner core. We have developed a physical model to explain these seismic features. At the inner?outer boundary, the crystallization of Fe alloy co?exists with the residue melt producing a “snowing” slurry layer (F layer), consistent with observed seismic velocity gradient. Solid Fe alloy crystals accumulate and eventually compact at the top of the inner core, and may exhibit lateral variations in thickness between the east?west hemispheres. Our model can explain the east?west asymmetry observed in the seismic velocity. Our model uses mineral physics and seismological results to provide a holistic view of the physical and chemical processes for the inner?core growth over geological time.
DS202012-2257
2020
Zhang, Z., Fedortchouk, Y., Hanley, J.J., Kerr, M.Diamond resorption and immiscibility of C-O-H fluid in kimberlites: evidence from experiments in H2O-CO2-SiO2-MgO-CaO system at 1-3 GPa.Lithos, in press available 15p. PdfMantlediamond morphology

Abstract: Kimberlites are the deepest sourced magmas emplaced at the Earth's surface. They provide a “window” into the processes at the base of the subcratonic mantle. A better understanding of the origin, composition, and emplacement mechanisms of kimberlites is hampered by uncertainties in the contents of the two main volatiles, H2O and CO2. Diamond dissolution in H2O and in CO2 fluids produces distinct resorption features offering an opportunity to determine the composition of the magmatic fluid in kimberlites. Here we examined the relationship between H2O:CO2 ratio of the fluid and the style of diamond resorption by conducting experiments in C-O-H fluid saturated with silicates with variable H2O:CO2 ratios at the conditions of kimberlite ascent of 1-3 GPa and 1150-1350 °C. Our results showed that the geometry of etch pits on diamond and the resorption style evolve consistently as bulk CO2 content of the fluid changes from 0 to 50 to 50-90 and 90-100 mol%. The fluid composition at the run conditions was monitored by entrapment of synthetic fluid inclusions in olivine and quartz. The inclusions demonstrated the existence of a fluid miscibility gap at 1-3 GPa and 1250 °C with two fluid endmembers, an aqueous and a carbonic phase, which H2O:CO2 ratio at 1 GPa determined with confocal Raman microscopy is (H2O)0.62(CO2)0.38 and (H2O)0.12(CO2)0.88 respectively. Hence, diamond resorption morphology depends on the proportions of the end-member aqueous and carbonic fluids, which vary with the bulk composition of the fluid. The different density and ability of aqueous and carbonic fluids to dissolve silicates (olivine) would promote their separation in the rising magma column. Concentration of the lower density aqueous fluid towards the tip of the propagating dyke would facilitate more efficient fracturing of the country rocks and faster ascent of the kimberlite magma causing explosive eruption. We propose that preferential attachment of aqueous fluid bubbles would help to increase the buoyancy of olivine xenocrysts and possibly diamond in the kimberlite magma offering a mechanism for transporting the heavy mantle cargo.
DS202009-1676
2020
Zheng, H., Chen, H., Wu, C., Jiang, H., Gao, C., Kang, Q., Yang, C., Wang, D., Lai, C-K.Genesis of the supergiant Huayangchuan carbonatite-hosted uranium polymetallic deposit in the Qinling orogen, central China.Gondwana Research, Vol. 86, pp. 250-265.ChinaREE

Abstract: The newly-discovered supergiant Huayangchuan uranium (U)-polymetallic deposit is situated in the Qinling Orogen, Central China. The deposit contains economic endowments of U, Nb, Pb, Se, Sr, Ba and REEs, some of which (e.g., U, Se, and Sr) reaching super-large scale. Pyrochlore, allanite, monazite, barite-celestite and galena are the major ore minerals at Huayangchuan. Uranium is mainly hosted in the primary mineral of pyrochlore, and the mineralization is mainly hosted in or associated with carbonatite dikes. According to the mineral assemblages and crosscutting relationships, the alteration/mineralization at Huayangchuan comprises four stages, i.e., pegmatite REE mineralization (I), main mineralization (II), skarn mineralization (III) and post-ore alteration (IV). Coarse-grained euhedral allanite is the main Stage I REE mineral, and the pegmatite-hosted REE mineralization (ca. 1.8 Ga) occurs mostly in the shallow-level of northwestern Huayangchuan, corresponding to the Paleoproterozoic Xiong'er Group volcanic rocks (1.80-1.75 Ga) in the southern margin of North China Block. Carbonatite-hosted Stage II mineralization contributes to the majority of U-Nb-REE-Ba-Sr resources, and is controlled by the Huayangchuan Fault. Stage II mineralization can be further divided into the sulfate mineralization (barite-celestite) (II-A), alkali-rich U mineralization (aegirine-augite + pyrochlore + uraninite + uranothorite) (II-B) and REE (allanite + monazite + chevkinite)-U (pyrochlore + uraninite) mineralization (II-C) substages. Stage II mineralization may have occurred during the Late Triassic Mianlue Ocean closure. Skarn mineralization contributed to the majority of Pb and minor U-REE (uraninite-allanite) resources at Huayangchuan, and is spatially associated with the Late Cretaceous-Early Jurassic (Yanshanian) Huashan and Laoniushan granites. We suggested that hydrothermal fluids derived from the Laoniushan and Huashan granites may have reacted with the Triassic carbonatites, and formed the Huayangchuan Pb skarn mineralization. The mantle-derived Triassic carbonatites may have been fertilized by the U-rich subducting oceanic sediments, and were further enriched through reacting with the Proterozoic U-REE-rich pegmatite wallrocks at Huayangchuan. Ore-forming elements were likely transported in metal complexes (F?, and ), and deposited with the dilution of the complex concentration. This may have formed the distinct vertical mineralization zoning, i.e., sodic fenite-related alkali-U mineralization at depths and potassic fenite-related REE-U mineralization at shallow level.
DS202012-2258
2020
Zheng, H., Chen, H., Wu, C., Jiang, H., Gao, C., Kang, Q., Yang, C., Wang, D., Lai, C-k.Genesis of the supergiant Huayanchuan carbonatite-hosted uranium-plymetallic deposit in the Qinling Orogen, central China.Gondwana Research, Vol. 86, pp. 250-265. pdfChinadeposit - Huayangchuan

Abstract: The newly-discovered supergiant Huayangchuan uranium (U)-polymetallic deposit is situated in the Qinling Orogen, Central China. The deposit contains economic endowments of U, Nb, Pb, Se, Sr, Ba and REEs, some of which (e.g., U, Se, and Sr) reaching super-large scale. Pyrochlore, allanite, monazite, barite-celestite and galena are the major ore minerals at Huayangchuan. Uranium is mainly hosted in the primary mineral of pyrochlore, and the mineralization is mainly hosted in or associated with carbonatite dikes. According to the mineral assemblages and crosscutting relationships, the alteration/mineralization at Huayangchuan comprises four stages, i.e., pegmatite REE mineralization (I), main mineralization (II), skarn mineralization (III) and post-ore alteration (IV). Coarse-grained euhedral allanite is the main Stage I REE mineral, and the pegmatite-hosted REE mineralization (ca. 1.8 Ga) occurs mostly in the shallow-level of northwestern Huayangchuan, corresponding to the Paleoproterozoic Xiong'er Group volcanic rocks (1.80-1.75 Ga) in the southern margin of North China Block. Carbonatite-hosted Stage II mineralization contributes to the majority of U-Nb-REE-Ba-Sr resources, and is controlled by the Huayangchuan Fault. Stage II mineralization can be further divided into the sulfate mineralization (barite-celestite) (II-A), alkali-rich U mineralization (aegirine-augite + pyrochlore + uraninite + uranothorite) (II-B) and REE (allanite + monazite + chevkinite)-U (pyrochlore + uraninite) mineralization (II-C) substages. Stage II mineralization may have occurred during the Late Triassic Mianlue Ocean closure. Skarn mineralization contributed to the majority of Pb and minor U-REE (uraninite-allanite) resources at Huayangchuan, and is spatially associated with the Late Cretaceous-Early Jurassic (Yanshanian) Huashan and Laoniushan granites. We suggested that hydrothermal fluids derived from the Laoniushan and Huashan granites may have reacted with the Triassic carbonatites, and formed the Huayangchuan Pb skarn mineralization. The mantle-derived Triassic carbonatites may have been fertilized by the U-rich subducting oceanic sediments, and were further enriched through reacting with the Proterozoic U-REE-rich pegmatite wallrocks at Huayangchuan. Ore-forming elements were likely transported in metal complexes (F?, and ), and deposited with the dilution of the complex concentration. This may have formed the distinct vertical mineralization zoning, i.e., sodic fenite-related alkali-U mineralization at depths and potassic fenite-related REE-U mineralization at shallow level.
DS202011-2071
2020
Zhimulev, E.I., Babich, Yu.V., Karpovich, Z.A., Chepurov, A.I., Pokhilenko, N.P.Low nitrogen diamond growth in Fe-C-S system.Doklady Earth Sciences, Vol. 494, 1, pp. 696-698.Russiadiamond genesis

Abstract: The first results on diamond growth in the Fe-?-S system with 1 wt % S (relative to Fe) at 6 GPa and 1450°C have been reported. The diamonds obtained contain about 30 ppm N, on average, and belong to the low-N transition diamond group Ib-IIa. It has been suggested that the reduction conditions formed by certain active elements such as S can play an important role in the formation of natural low-N diamonds.
DS202004-0550
2019
Zienko, S.I., Slabkovskii, D.S.A comparative analysis of the luminescence spectra of diamonds.Optics and Spectroscopy, Vol. 127, 3, pp. 564-570. doi.org/10.3390/min100100018Globalluminescence

Abstract: To identify the signs that distinguish natural diamonds from artificial diamonds, a comparative analysis of the luminescence spectra with regards to the Q factor, center of gravity, bandwidth parameter, and energy losses in the diamond crystal lattice under conditions of ohmic and dielectric relaxation of luminescence is performed. The phenomenon of resonant luminescence in the femtosecond time range is detected in diamond. It is established that natural and artificial diamonds noticeably differ in the relaxation frequency and in the energy of resonant radiation.
DS202003-0374
2020
Zubkova, N.V., Chukanov, N.V., Schaefer, C., Kan, K.V., Pekov, I., Pushcharovsky, D.Yu.A1 analogue of chayesite from a lamproite of Canacarix, SE Spain, and its crystal structure.Journal of Mineralogy and Geochemistry ( formerly Neues Jahrbuch fur Mineralogie), in press NOT availableEurope, Spainlamproite
DS202008-1462
2020
Zubkova, N.V., Chukanov, N.V., Schafer, C., van Konstantin, V., Pekov,I.V., Pushcharovsky, D. Yu.Al analogue of chayvesite from a lamproite of Cancarix, SE Spain, and its crystal structure.Neues Jahbuch fur Mineralogie, Vol. 196, 3, pp. 193-196.Europe, Spainlamproite

Abstract: Al analogue of chayesite (with Al > Fe3+) was found in a lamproite from Cancarix, SE Spain. The mineral forms green thick-tabular crystals up to 0.4 mm across in cavities. The empirical formula derived from EMP measurements and calculated on the basis of 17 Mg + Fe + Al + Si apfu is (K0.75 Na0.20 Ca0.11)Mg3.04 Fe0.99 Al1.18 Si11.80 O30. The crystal structure was determined from single crystal X-ray diffraction data ( R = 2.38%). The mineral is hexagonal, space group P 6/ mcc, a = 10.09199(12), c = 14.35079(19) Å, V = 1265.78(3) Å3, Z = 2. Fe is predominantly divalent. Al is mainly distributed between the octahedral A site and the tetrahedral T 2 site. The crystal chemical formula derived from the structure refinement is C (K0.73 Na0.16 Ca0.11) B (Na0.02)4 A (Mg0.42 Al0.29 Fe0.29)2 T 2(Mg0.71 Fe0.16 Al0.13)3 T 1(Si0.985 Al0.015)12 O30.
 
 

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