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The Sheahan Diamond Literature Reference Compilation - Scientific and Media Articles based on Major Keyword - Impact Crater
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 announcements called 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 Keyword Index
Sheahan Diamond Literature Reference Compilation - Scientific Articles by Author for all years
Each article reference in the SDLRC is tagged with one or more key words assigned by Pat Sheahan to highlight the main topics of the article. In an effort to make it easier for users to track down articles related to a specific topic, KRO has extracted these key words and developed a list of major key words presented in this Key Word Index to which individual key words used in the article reference have been assigned. In most of the individual Key Word Reports the references are in crhonological order, though in some such as Deposits the order is first by key word and then chronological. Only articles classified as "technical" (mainly scientific journal articles) and "media" (independent media articles) are included in the Key Word Index. References that were added in the most recent monthly update are highlighted in yellow.
An Impact Crater is the depression created in the earth's crust when struck by an asteroid or meteor. The moon is full of such completely preserved impact craters, but on the earth they are only preserved when fairly recent or within a stable craton. Scientific articles about impact craters are relevant to diamonds because major impacts can affect melting behavior within the earth's mantle which leads to magmatism which in turn can spawn kimberlite emplacement. Extraterrestrial impacts also create high pressure and high temperature conditions that support diamond formation, though so-called impact diamonds tend to be small and have a hexagonal crystal structure similar to graphite.
The Cretaceous/Tertiary boundary interval, Raton Basin, Colorado and New Mexico and its content of shock metamorphosed minerals evidence relevant K/Tboundary
Geological Society of America, Paper No. 249, 104p. $ 30.00 United States
The Precambrian Earth, tempos and events, editors Eriksson, P.G., Altermann, W., Nelson, D.R., Mueller, W.U., Elsevier, Developments in Precambrian Geology No. 12, C
Abstract: Earth was a completely different planet more than 2.5 billion years ago. Little is known about this critical time when cratonic continental seeds formed; life emerged; and precious mineral resources concentrated. Our knowledge is limited because plate tectonic processes destroyed most of this early record. In contrast, Earth's sister, Venus -- similar in size, density, bulk composition, and distance from the Sun -- never developed plate tectonics. Venus also lacks a water cycle. Like siblings, Venus and Earth were most similar in their youth; however, Venus preserves a more complete geological record of its infancy, including both exogenic and endogenic features. Applying clues from Venus, Vicky L. Hansen proposes a new hypothesis for the formation of Earth's cratons. Large bolides pierced early thin lithosphere causing massive partial melting in the ductile mantle; melt escaped upward, forming cratonic crust; meanwhile strong, dry, buoyant melt residue formed cratonic roots, serving as unique buoyant life preservers during future plate-tectonic recycling.
Boletin del Museo Nacional de Historia Narural del Paraguay, Vol. 20, 2, pp. 205-213. pdf available in * Port
South America, Paraguay
Impact Crater
Abstract: We report here the discovery and study of several new modeled large impact craters in Eastern Paraguay, South America. They were studied by geophysical information (gravimetry, magnetism), field geology and also by microscopic petrography. Clear evidences of shock metamorphic effects were found (e.g., diaplectic glasses, PF, PDF in quartz and feldspar) at 4 of the modeled craters: 1) Negla: diameter:~80-81 km., 2) Yasuka Renda D:~96 km., 3) Tapyta, D: ~80 km. and 4) San Miguel, D: 130-136 km. 5) Curuguaty, D: ~110 km. was detected and studied only by geophysical information. Target-rocks range goes from the crystalline Archaic basement to Permian sediments. The modeled craters were in some cases cut by tholeiitic/alkaline rocks of Mesozoic age and partially covered by lavas of the basaltic Mesozoic flows (Negla, Yasuka Renda, Tapyta and Curuguaty). One of them was covered in part by sediments of Grupo Caacupé (age: Silurian/Devonian). Some of these modeled craters show gold, diamonds, uranium and REE mineral deposits associated. All new modeled large impact craters are partially to markedly eroded.
International Journal of Astronomy and Astrophysics, Vol. 1, pp. 98-104.
Asia, Mongolia
astropipes, impact craters
Abstract: In this paper we present summation of eighteen year’s investigation of the all gold and diamond-bearing astropipes of Mongolia. Four astropipe structures are exemplified by the Agit Khangay (10 km in diameter, 470 38' N; 960 05' E), Khuree Mandal (D=11 km; 460 28' N; 980 25' E), Bayan Khuree (D=1 km; 440 06' N; 1090 36' E), and Tsenkher (D=7 km; 980 21' N; 430 36' E) astropipes of Mongolia. Detailed geological and gas-geochemical investigation of the astropipe structures show that diamond genesis is an expression of collision of the lithospheric mantle with the explosion process initiated in an impact collapse meteor crater. The term "astropipes" (Dorjnamjaa et al., 2010, 2011) is a neologism and new scientific discovery in Earth science and these structures are unique in certain aspects. The Mongolian astropipes are genuine "meteorite crater" structures but they also contain kimberlite diamonds and gold. Suevite-like rocks from the astropipes contain such minerals, as olivine, coesite, moissanite (0,6 mm), stishovite, coesite, kamacite,tektite, khamaravaevite (mineral of meteorite titanic carbon), graphite-2H, khondrite, picroilmenite, pyrope, phlogopite, khangaite (tektite glass, 1,0-3,0 mm in size), etc. Most panned samples and hand specimens contain fine diamonds with octahedrol habit (0, 2-2,19 mm, 6,4 mg or 0,034-0,1 carat) and gold (0,1-5 g/t). Of special interest is the large amount of the black magnetic balls (0,05-5,0 mm) are characterized by high content of Ti, Fe, Co, Ni, Cu, Mn, Mg, Cd, Ga, Cl, Al, Si, K. Meanwhile, shatter cones (size approx. 1.0 m) which are known from many meteorite craters on the Earth as being typical of impact craters were first described by us Khuree Mandal and Tsenkher astropipe structures. All the described meteorite craters posses reliable topographic, geological, mineralogical, geochemical, and aerospace mapping data, also some geophysical and petrological features (especially shock metamorphism) have been found, all of which indicate that these structures are a proven new type of gold-diamond-bearing impact structure, termed here "astropipes". The essence of the phenomenon is mantle manifestation and plume of a combined nuclear-magma-palingenesis interaction.
Abstract: Ring, dome and crater features on the Australian continent and shelf include (A) 38 structures of confirmed or probable asteroid and meteorite impact origin and (B) numerous buried and exposed ring, dome and crater features of undefined origin. A large number of the latter include structural and geophysical elements consistent with impact structures, pending test by field investigations and/or drilling. This paper documents and briefly describes 43 ring and dome features with the aim of appraising their similarities and differences from those of impact structures. Discrimination between impact structures and igneous plugs, volcanic caldera and salt domes require field work and/or drilling. Where crater-like morphological patterns intersect pre-existing linear structural features and contain central morphological highs and unique thrust and fault patterns an impact connection needs to tested in the field. Hints of potential buried impact structures may be furnished by single or multi-ring TMI patterns, circular TMI quiet zones, corresponding gravity patterns, low velocity and non-reflective seismic zones. A) Examples of crater-form and dome-form features containing elements consistent with an impact origin, though unproven, include Auvergne, Delamere, Fiery Creek, Monte Christo, Mount Moffatt, Tanami East, Youngerina, and Tingha. B) Examples of buried multi-ring features of possible to probable impact origin include Augathella, Balfour Downs, Calvert Hills, Camooweal, Green Swamp Well, Herbert, Ikybon River, Ilkurka, Lennis, McLarty Hills, Mount Davies, Mulkara; Neale; Sheridan Creek, Oodjuongari and Renehan. C) Examples of igneous plugs unrelated to impacts include the Monto gabbro and numerous circular granitoid plugs such as Windinie Hills granite and Yataga granodiorite. D) Large circular structures such as Mount Ashmore and Gnargoo are considered to have convincing structural deformation features warranting classification as probable impact structures. The origin of very large circular TMI and gravity patterns such as of the Diamantina River drainage feature, Coonamona anomaly and the multiple TMI ring pattern of the Deniliquin-Booligal remain unresolved. The advent of ~ 40 m TMI grid coverage promises to further uncover ring and dome features, such as the McLarty Hills multi-ring feature, potentially increasing the inventory of ring structures on the Australian continent. Compared with frequency distribution patterns of extra-terrestrial impact structures worldwide, the Australian record displays a relatively common occurrence of large impact structures and relative depletion in small impact structures and craters. This is explained by the better preservation of large structures at deep crustal zones as compared to the erosion of small craters.
Abstract: Impact cratering is a dynamic process that is violent and fast. Quantifying processes that accommodate deformation at different scales during central uplift formation in complex impact structures is therefore a challenging task. The ability to correlate mineral deformation at the microscale with macroscale processes provides a critical link in helping to constrain extreme crustal behavior during meteorite impact. Here we describe the first high-pressure-phase-calibrated chronology of shock progression in zircon from a central uplift. We report both shock twins and reidite, the high-pressure ZrSiO4 polymorph, in zircon from shocked granitic gneiss drilled from the center of the >60-km-diameter Woodleigh impact structure in Western Australia. The key observation is that in zircon grains that contain reidite, which forms at >30 GPa during the crater compression stage, the reidite domains are systematically offset by later-formed shock deformation twins (?20 GPa) along extensional planar microstructures. The {112} twins are interpreted to record crustal extension and uplift caused by the rarefaction wave during crater excavation. These results provide the first physical evidence that relates the formation sequence of both a high-pressure phase and a diagnostic shock microstructure in zircon to different cratering stages with unique stress regimes that are predicted by theoretical and numerical models. These microstructural observations thus provide new insight into central uplift formation, one of the least-understood processes during complex impact crater formation, which can produce many kilometers of vertically uplifted bedrock in seconds.
Diamond & Related Materials, Vol. 91, pp. 207-212.
Russia, Siberia
Popigai
Abstract: We report the results of a study of the polycrystalline powder of the diamond-lonsdaleite from the Popigai crater (Siberia) using UV micro-Raman spectroscopy and high-resolution synchrotron X-ray diffraction. By subtracting two experimental Raman spectra of diamond-lonsdaleite samples with close amounts of diamond and lonsdaleite, we were able to identify the polytypic composition of impact diamonds in contrast to the method of X-ray diffraction. We have managed to get for the first time the spectrum of “pure” lonsdaleite. Its deconvolution has allowed us to identify all the three Raman - active vibrational modes E2g, A1g, and E1g whose positions agree well with the results of ab initio calculations.
Abstract: Earth’s status as the only life-sustaining planet is a result of the timing and delivery mechanism of carbon (C), nitrogen (N), sulfur (S), and hydrogen (H). On the basis of their isotopic signatures, terrestrial volatiles are thought to have derived from carbonaceous chondrites, while the isotopic compositions of nonvolatile major and trace elements suggest that enstatite chondrite-like materials are the primary building blocks of Earth. However, the C/N ratio of the bulk silicate Earth (BSE) is superchondritic, which rules out volatile delivery by a chondritic late veneer. In addition, if delivered during the main phase of Earth’s accretion, then, owing to the greater siderophile (metal loving) nature of C relative to N, core formation should have left behind a subchondritic C/N ratio in the BSE. Here, we present high pressure-temperature experiments to constrain the fate of mixed C-N-S volatiles during core-mantle segregation in the planetary embryo magma oceans and show that C becomes much less siderophile in N-bearing and S-rich alloys, while the siderophile character of N remains largely unaffected in the presence of S. Using the new data and inverse Monte Carlo simulations, we show that the impact of a Mars-sized planet, having minimal contributions from carbonaceous chondrite-like material and coinciding with the Moon-forming event, can be the source of major volatiles in the BSE.
Abstract: Impactors of different types and sizes can produce a final crater of the same diameter on a planet under certain conditions. We derive the condition for such “isocrater impacts” from scaling laws, as well as relations that describe how the different impactors affect the interior of the target planet; these relations are also valid for impacts that are too small to affect the mantle. The analysis reveals that in a given isocrater impact, asteroidal impactors produce anomalies in the interior of smaller spatial extent than cometary or similar impactors. The differences in the interior could be useful for characterizing the projectile that formed a given crater on the basis of geophysical observations and potentially offer a possibility to help constrain the demographics of the ancient impactor population. A series of numerical models of basin-forming impacts on Mercury, Venus, the Moon, and Mars illustrates the dynamical effects of the different impactor types on different planets. It shows that the signature of large impacts may be preserved to the present in Mars, the Moon, and Mercury, where convection is less vigorous and much of the anomaly merges with the growing lid. On the other hand, their signature will long have been destroyed in Venus, whose vigorous convection and recurring lithospheric instabilities obliterate larger coherent anomalies.
Nature Scientific Reports, doi.org/10.1038/ s41598-019-46556-3 8p. Pdf
Global
diamond morphology, impact craters
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.
Abstract: In 1992 Rampino noticed a large, almost circular negative gravity anomaly (~30 mGal) on the Falkland Plateau to the WNW of Malvinas Islands/Falklnad Islands using satellite data then available, and speculated that it might be associated with a large (~250 km wide?) buried impact structure. In some more recent compilations Rocca & Presser (2015) and Rocca et al. (2017) was attended the Malvinas Islands/Falklnad Islands “buried impact structure” with particular care; but also these works was harshly criticized. The present text, which is an advance to demonstrate the certain possibilities that this Malvinas Islands/Falklnad Islands It could really be a very probable mega impact structure, gathers shows and evaluates the existing and available indirect information; like gravimetry (Isostasy, Free-air and Bouguer); seismic reflection (Geco Prakla); and, even commenting aspects of its magnetic behavior and its local geology. In all gravimetric analyses from the Malvinas Islands/Falklnad Islands “buried impact structure” it can be shown that an annulus of positive gravity anomaly surrounding a circular oval depression of negative (isostasy and Free-air)/much lower (Bouguer) values gravity anomaly. The most relevant gravimetric information would be the near circular to oval Bouguer gravity low anomaly (with a minimum value of ~150 mGal) surrounded by at least circular ~255 kilometers wide circular ring of positive gravity anomaly (maximum ~225 mGal); a very high values of Bouguer anomaly that are highly compatible with what is expected to be found in mega impact structures. The Malvinas probable impact structure shows almost 100 mGal superior to the volcanic complex of Iceland; so it seems obvious that Malvinas probable impact structure moves away from a speculation by mega-paleo-volcano origin. When gravimetrically modeled, a probable peak ring of ~255 km is evidenced; as well as, the inferred the ~550 km probable rim-crest; configuration that reproduces an almost perfect and symmetrical modeling of a very probable giant impact structure with its clear visible the very probable elements: rim crest-annulus basin-peak ring-central basin-peak ring-annulus basin-rim crest. Four Geco Prakla seismic reflection lines on the area located to the SW of the potential peak ring show a vertical and disturbed crystalline basement (the “peak ring”); in three of them, the “central basin” what would it be filled with sediments after impact (probable ejecta). Using the empirical formula of Assumpção et al. (2013) calculation for crustal thickness could be found very clearly strong CT distortion along Malvinas very probable giant impact structure: around 3400-4000 meters; as is to be expected in terrestrial mega impact structure. Harness the EMAG2v3 a global Earth Magnetic Anomaly Grid compiled from satellite (Meyer et al., 2017) for the Malvinas very probable giant impact structure a well superior anomaly was found and better definition than observed, using the same information, to the one characterized by the impact crater Chicxulub. The geological map of the Falkland Islands Government that was placed on top of the modeling isostasy gravimetric map where the approximate circumference of the very probable peak-ring and the very probable rim-crest is highlighted. This information allows to see that the largest island (West Malvinas) would be part of the very probable peak-ring and the smaller island (East Malvinas) would be part of the very probable rim-crest; both separated by the depression that would correspond to the very probable annulus basin. Based on what was analyzed in the Malvinas Islands area, we concluded the Malvinas exhibited geophysics traits of a large ancient asteroid impact; i.e. Malvinas very probable giant impact structure. Very probable impact structure what could be among one of the world's largest impact crater.
Abstract: In the outback of Western Australia, researchers have shown that shocked rocks were forged 2.229 billion years ago, when an asteroid crashed into our planet. The finding makes Yarrabubba crater, the 70-kilometer-wide scar left by the collision, Earth's oldest. The geologists who reported the date last week, at the Goldschmidt geochemistry conference, also point out a conspicuous coincidence: The impact came at the tail end of a planetwide deep freeze known as Snowball Earth. They say the impact may have helped thaw Earth by vaporizing thick ice sheets and lofting steam into the stratosphere, creating a powerful greenhouse effect. Other researchers are skeptical that Yarrabubba—which is just one-third the size of the crater left by the dinosaur-killing impact 66 million years ago—could have had such a profound effect on the climate. Still, they say, paleoclimate studies should consider the possible role of such violent collisions.
Journal of the Geological Society, Vol. 76, pp. 817-829.
Europe, Scotland
impact crater
Abstract: The Lairg Gravity Low may represent a buried impact crater c. 40 km across that was the source of the 1.2 Ga Stac Fada Member ejecta deposit but the gravity anomaly is too large to represent a simple crater and there is no evidence of a central peak. Reanalysis of the point Bouguer gravity data reveals a ring of positive anomalies around the central low, suggesting that it might represent the eroded central part of a larger complex crater. The inner or peak rings of complex craters show a broadly consistent 2:1 relationship between ring diameter and total crater diameter, implying that the putative Lairg crater may be as much as 100 km across. This would place the crater rim within a few kilometres of the Stac Fada Member outcrop, a location inconsistent with the thickness and clast size of the ejecta deposit. We propose that the putative impact crater originally lay further east, substantially further from the Stac Fada Member than today, and was translocated westwards to its present location beneath Lairg during the Caledonian Orogeny. This model requires that a deep-seated thrust fault, analogous to the Flannan and Outer Isles thrusts, exists beneath the Moine Thrust in north-central Scotland.
Pyroclastic Flow Journal of Geology, Vol. 9, no. 1, pp. 1-14. pdf.
Antarctica
impact structure
Abstract: In 1992 Rampino noticed a large, almost circular negative gravity anomaly (~30 mGal) on the Falkland Plateau to the WNW of Malvinas Islands/Falkland Islands using satellite data then available, and speculated that it might be associated with a large (~250 km wide?) buried impact structure. In some more recent compilations Rocca & Presser (2015) and Rocca et al. (2017) was attended the Malvinas Islands/Falkland Islands “buried impact structure” with particular care; but also these works was harshly criticized. The present text, which is an advance to demonstrate the certain possibilities that this Malvinas Islands/Falklnad Islands It could really be a very probable mega impact structure, gathers shows and evaluates the existing and available indirect information; like gravimetry (Isostasy, Free-air and Bouguer); seismic reflection (Geco Prakla); and, even commenting aspects of its magnetic behavior and its local geology. In all gravimetric analyses from the Malvinas Islands/Falklnad Islands “buried impact structure” it can be shown that an annulus of positive gravity anomaly surrounding a circular oval depression of negative (isostasy and Free-air)/much lower (Bouguer) values gravity anomaly. The most relevant gravimetric information would be the near circular to oval Bouguer gravity low anomaly (with a minimum value of ~150 mGal) surrounded by at least circular ~255 kilometers wide circular ring of positive gravity anomaly (maximum ~225 mGal); a very high values of Bouguer anomaly that are highly compatible with what is expected to be found in mega impact structures. The Malvinas probable impact structure shows almost 100 mGal superior to the volcanic complex of Iceland; so it seems obvious that Malvinas probable impact structure moves away from a speculation by mega-paleo-volcano origin. When gravimetrically modeled, a probable peak ring of ~255 km is evidenced; as well as, the inferred the ~550 km probable rim-crest; configuration that reproduces an almost perfect and symmetrical modeling of a very probable giant impact structure with its clear visible the very probable elements: rim crest-annulus basin-peak ring-central basin-peak ring-annulus basin-rim crest. Four Geco Prakla seismic reflection lines on the area located to the SW of the potential peak ring show a vertical and disturbed crystalline basement (the “peak ring”); in three of them, the “central basin” what would it be filled with sediments after impact (probable ejecta). Using the empirical formula of Assumpção et al. (2013) calculation for crustal thickness could be found very clearly strong CT distortion along Malvinas very probable giant impact structure: around 3400-4000 meters; as is to be expected in terrestrial mega impact structure. Harness the EMAG2v3 a global Earth Magnetic Anomaly Grid compiled from satellite (Meyer et al., 2017) for the Malvinas very probable giant impact structure a well superior anomaly was found and better definition than observed, using the same information, to the one characterized by the impact crater Chicxulub. The geological map of the Falkland Islands Government that was placed ontop of the modeling isostasy gravimetric map where the approximate circumference of the very probable peak-ring and the very probable rim-crest is highlighted. This information allows to see that the largest island (West Malvinas) would be part of the very probable peak-ring and the smaller island (East Malvinas) would be part of the very probable rim-crest; both separated by the depression that would correspond to the very probable annulus basin. Based on what was analyzed in the Malvinas Islands area, we concluded the Malvinas exhibited geophysics traits of a large ancient asteroid impact; i.e. Malvinas very probable giant impact structure. Very probable impact structure what could be among one of the world's largest impact crater.
Diamonds & Related Materials, Vol. 101, 107640, 13p. Pdf
Russia
Popigai
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.
Abstract: Astrobiology is one of the actively studied fields aimed to answer the question about the Earth life origin. The detail studies of the organic matter could give a key for understanding about possible conditions for preservation of the biological material at the extreme conditions of the giant impact events and meteorite fallings. In the context of the astrobiological problem the recent discovery of diamond fossils is very informative and impressive [1, 2]. Here we describe in short the features of the impact-preserved organic relicts in the diamond state having relict fragments of cellulose and lignin, pointing to possibility to save organics even under the conditions of diamond formation. Impact Diamonds: Almost 50 years have passed since the discovery of impact diamonds. Currently, several varieties of impact diamonds are known in natural geological objects, determined by the type of carbon precursor, that define their formation mechanisms and structural features. Actually, aftergraphite, after-coal and after-organic diamonds are known [1-5]. The latter usually present in the form of diamond fossils after plant fragments. After-Graphitic Impact Diamonds: The aftergraphitic diamonds were discovered in the 70s of the XX century in the largest Popigai astrobleme with a diameter of about 100 km, bearing giant reserves of valuable technical diamond raw materials [3, 4]. This type of impact diamonds is formed by solid-state transformation of the graphite precursor structure to diamond with a diffusion-free mechanism forming micropolycrystalline aggregates with submicrometersized crystals [1]. This variety is characterized by polyphase aggregates with possible substantial amount of hexagonal packaging defects (named “lonsdaleite”) within the cubic diamond structure [6]. It may also include an admixture of relict graphite, amorphous and onion-like carbon [7, 8]. Currently, apographic diamonds have been discovered in several deposits, for example diamond-rich Popigai and Puchezh-Katunki in Russia, Ries (Germany), Sudbury (Canada). After-Coal Impact Diamonds: After-coal impact diamonds were discovered a bit later, they were found in the giant Kara astrobleme in 80s of the XX century [3, 4]. This diamond type was formed by short-distance diffusion mechanism from coalificated carboniferous particles from the host sedimentary rocks, described in detail in [5]. The diamonds have crystallites size about 20-50 nm, differ from the after-graphitic variety by presence of ideal octahedral crystallite shapes and dislocation-free (lonsdaleite-free) structure [2]. By present the after-coal diamonds are known only at the Kara astrobleme and near-set Ust`-Kara impactites. After-Organic Diamonds (Diamond Fossils): The diamond fossils have been just discovered. The first find has been found out within melt fragment within suevitic breccia at the Kara astrobleme (Fig. 1). The diamonds are presented with well preserved relict cell micromorphology and have very specific structure, composition and spectroscopic features studied and described in detail in [1].
Abstract: Astrobiology is one of the actively studied fields aimed to answer the question about the Earth life origin. The detail studies of the organic matter could give a key for understanding about possible conditions for preservation of the biological material at the extreme conditions of the giant impact events and meteorite fallings. In the context of the astrobiological problem the recent discovery of diamond fossils is very informative and impressive [1, 2]. Here we describe in short the features of the impact-preserved organic relicts in the diamond state having relict fragments of cellulose and lignin, pointing to possibility to save organics even under the conditions of diamond formation. Impact Diamonds: Almost 50 years have passed since the discovery of impact diamonds. Currently, several varieties of impact diamonds are known in natural geological objects, determined by the type of carbon precursor, that define their formation mechanisms and structural features. Actually, aftergraphite, after-coal and after-organic diamonds are known [1-5]. The latter usually present in the form of diamond fossils after plant fragments. After-Graphitic Impact Diamonds: The aftergraphitic diamonds were discovered in the 70s of the XX century in the largest Popigai astrobleme with a diameter of about 100 km, bearing giant reserves of valuable technical diamond raw materials [3, 4]. This type of impact diamonds is formed by solid-state transformation of the graphite precursor structure to diamond with a diffusion-free mechanism forming micropolycrystalline aggregates with submicrometersized crystals [1]. This variety is characterized by polyphase aggregates with possible substantial amount of hexagonal packaging defects (named “lonsdaleite”) within the cubic diamond structure [6]. It may also include an admixture of relict graphite, amorphous and onion-like carbon [7, 8]. Currently, apographic diamonds have been discovered in several deposits, for example diamond-rich Popigai and Puchezh-Katunki in Russia, Ries (Germany), Sudbury (Canada). After-Coal Impact Diamonds: After-coal impact diamonds were discovered a bit later, they were found in the giant Kara astrobleme in 80s of the XX century [3, 4]. This diamond type was formed by short-distance diffusion mechanism from coalificated carboniferous particles from the host sedimentary rocks, described in detail in [5]. The diamonds have crystallites size about 20-50 nm, differ from the after-graphitic variety by presence of ideal octahedral crystallite shapes and dislocation-free (lonsdaleite-free) structure [2]. By present the after-coal diamonds are known only at the Kara astrobleme and near-set Ust`-Kara impactites. After-Organic Diamonds (Diamond Fossils): The diamond fossils have been just discovered. The first find has been found out within melt fragment within suevitic breccia at the Kara astrobleme (Fig. 1). The diamonds are presented with well preserved relict cell micromorphology and have very specific structure, composition and spectroscopic features studied and described in detail in [1].