bluuebunny/crossref_metadata_2025_split huggingface dataset:
Popigai crater: Origin and distribution of diamond‐bearing impactites
Authors: MASAITIS V. L. 
Published: February 2010

Abstract— About three decades ago, a formerly unknown genetic type of natural diamonds was discovered in impact craters. Impact diamonds are currently known from a number of impact structures in Europe, Asia and North America, and it's likely that the number of finds will increase with time. The Popigai crater, Northern Siberia, where impact diamonds were first found, was specifically investigated in terms of geology, geophysics, petrography and mineralogy. Large resources of industrial impact diamonds were discovered, and these minerals were studied in detail.Authigenic impact diamonds occur in situ in shocked graphite‐bearing gneisses that are found as inclusions in impact melt rocks: tagamites and suevites. According to the observed transformation of coexisting minerals, the lower estimated pressure of the coherent martensite transition of graphite to diamonds is 35 GPa. Impact diamonds inherit the original shape of graphite crystals and are composed of a polycrystalline structured aggregate of cubic and probably hexagonal carbon microcrystals 1–5 μm across. Numerous properties of diamonds depend on the high density of defects in the crystal lattice. Allothigenic impact diamonds occur in rocks produced by the homogenization and solidification of impact melt, which originated from the complete fusion of graphite‐bearing precursor gneisses. These diamonds usually reflect the influence of the hot melt and are strongly corroded.Diamond‐bearing tagamites and suevites in the Popigai crater interior occur as extended lens and sheets bodies and also as irregular small bodies. Diamond distribution depends on the original abundance of precursor graphite in the target rocks, on the superimposed shock‐metamorphic zonation, and on the character of the ejection of shocked and melted material along different trajectories and azimuths. This has resulted in radial and concentric inhomogeneities in diamond distribution in the crater interior. On a second order, the distribution depends on the scale of melt contamination by clasts and fragments and by the duration of cooling of certain melt bodies and their constituents. Enrichment in diamonds at the margins of thick tagamite sheets is the result of rapid cooling, which prevents combustion of diamonds. A positive correlation between diamond content and the amount of phosphorus pentoxide in impactites indicates links to C and P probably in organic matter of the primary sedimentary rocks, which were subjected to granulitic metamorphism 2.4 Ga ago and melted at the time of impact 35.7 Ma ago.
Ion probe measurements of carbon and nitrogen in iron meteorites
Authors: SUGIURA NAOJI 
Published: February 2010

Abstract— Carbon and nitrogen distributions in iron meteorites, their concentrations in various phases, and their isotopic compositions in certain phases were measured by secondary ion mass spectrometry (SIMS). Taenite (and its decomposition products) is the main carrier of C, except for IAB iron meteorites, where graphite and/or carbide (cohenite) may be the main carrier. Taenite is also the main carrier of N in most iron meteorites unless nitrides (carlsbergite CrN or roaldite (Fe, Ni)4N) are present. Carbon and N distributions in taenite are well correlated unless carbides and/or nitrides are exsolved.There seem to be three types of C and N distributions within taenite. (1) These elements are enriched at the center of taenite (convex type). (2) They are enriched at the edge of taenite (concave type). (3) They are enriched near but some distance away from the edge of taenite (complex type). The first case (1) is explained as equilibrium distribution of C and N in Fe‐Ni alloy with M‐shape Ni concentration profile. The second case (2) seems to be best explained as diffusion controlled C and N distributions. In the third case (3), the interior of taenite has been transformed to the α phase (kamacite or martensite). Carbon and N were expelled from the α phase and enriched near the inner border of the remaining γ phase. Such differences in the C and N distributions in taenite may reflect different cooling rates of iron meteorites.Nitrogen concentrations in taenite are quite high approaching 1 wt% in some iron meteorites. Nitride (carlsbergite and roaldite) is present in meteorites with high N concentrations in taenite, which suggests that the nitride was formed due to supersaturation of the metallic phases with N. The same tendency is generally observed for C (i.e., high C concentrations in taenite correlate with the presence of carbide and/or graphite). Concentrations of C and N in kamacite are generally below detection limits.Isotopic compositions of C and N in taenite can be measured with a precision of several permil. Isotopic analysis in kamacite in most iron meteorites is not possible because of the low concentrations. The C isotopic compositions seem to be somewhat fractionated among various phases, reflecting closure of C transport at low temperatures. A remarkable isotopic anomaly was observed for the Mundrabilla (IIICD anomalous) meteorite. Nitrogen isotopic compositions of taenite measured by SIMS agree very well with those of the bulk samples measured by conventional mass spectrometry.
Geochemistry and petrology of lunar meteorite Queen Alexandra Range 94281, a mixed mare and highland regolith breccia, with special emphasis on very‐low‐titanium mafic components
Authors: JOLLIFF BRADLEY L. , KOROTEV RANDY L. , ROCKOW KAYLYNN M. 
Published: February 2010

Abstract— Queen Alexandra Range (QUE) 94281, a lunar meteorite recently discovered in Antarctica, is a glassy‐matrix, clast‐rich regolith breccia containing a mixture of mafic, volcanic‐glass and gabbroic constituents and a diverse set of highland constituents. In thin section, the clast assemblage is dominated by coarse mineral debris from a shallow intrusive or hypabyssal setting, or from deep within a thick mare flow. Abundant coarse‐grained pyroxene clasts have fine‐scale exsolution lamellae and compositions similar to pyroxenes of known lunar very‐low‐Ti (VLT) basalts and other lunar meteorites of basaltic composition. Pyroxene compositions follow Fe‐enrichment extending to hedenbergite, which is associated with fayalite and cristobalite, indicating slow cooling. We refer to the protolith of the crystalline VLT component as VLT gabbro. Fragments of pyroclastic glasses that have high Fe and low Ti concentrations, similar to the pyroclastic green glasses known from Apollo samples, are common. Lithic clasts include abundant subrounded, glassy to cryptocrystalline, aluminous (∼17–30 wt% Al2O3) KREEP‐poor melt breccias of highland origin and a variety of other feldspathic impactites. On the basis of composition of our subsamples, QUE 94281 consists of ∼54 wt% mafic or “mare” components and 46 wt% feldspathic or “highland” components.The bulk composition of QUE 94281 is similar to that of Yamato (Y) 793274, but QUE 94281 has slightly greater concentrations of some siderophile elements and slightly lower concentrations of those elements contributed mainly by mafic constituents. Differences in siderophile element concentrations are consistent with longer surface exposure of QUE 94281. Minor differences in trace element variations of subsamples of the two meteorites suggest subtle differences in the composition of their highland constituents. Nonetheless, the overall similarity of compositions supports the possibility that they were ejected from the same source region on the Moon.The crystalline VLT component of QUE 94281 differs from those known from Apollo 17 and Luna 24 VLT lithologies and from that of basaltic breccia Elephant Moraine (EET) 87521. The VLT‐gabbro component and the ferroan VLT volcanic glasses in QUE 94281 have compositions that may be petrogenetically related by derivation from a common picritic parent composition, represented by an ultramafic glass found in QUE 94281.
Secondary calcium‐iron‐rich minerals in the Bali‐like and Allende‐like oxidized CV3 chondrites and Allende dark inclusions
Authors: KROT ALEXANDER N. , PETAEV MICHAEL I. , ZOLENSKY MICHAEL E. , KEIL KLAUS , SCOTT EDWARD R. D. , NAKAMURA KEIKO 
Published: February 2010

Abstract— We have characterized Ca‐Fe‐rich silicates (salite‐hedenbergite pyroxenes (Fs10–50Wo45–50), andradite (Ca3Fe2Si3O12), kirschsteinite (CaFeSiO4), and wollastonite (Ca3Si3O9)) in the type I chondrules and matrices in the Bali‐like and Allende‐like oxidized CV3 chondrites and Allende dark inclusions. In type I chondrules in the Bali‐like CV3 chondrites, metal is oxidized to magnetite; magnetite‐sulfide nodules are replaced by Ca‐Fe‐rich pyroxenes with minor andradite and pure fayalite. We infer that Ca‐Fe‐rich pyroxenes, andradite, fayalite, magnetite, and phyllosilicates (which occur in mesostases) formed at relatively low temperatures (<300 °C) in the presence of aqueous solutions. Thermodynamic analysis of phase relations in the Si‐Fe‐Ca‐O‐H system and large O isotopic fractionation of the coexisting magnetite and fayalite (∼20%) (Krot et al., 1998) are consistent with this interpretation.In type I chondrules in the Allende‐like CV3 chondrites and dark inclusions, magnetite‐sulfide nodules are replaced by Ca‐Fe‐rich pyroxenes and ferrous olivine; low‐Ca pyroxene and forsterite phenocrysts are rimmed and veined by ferrous olivine. It appear that the Ca‐Fe‐rich pyroxenes predate formation of ferrous olivine; the latter postdates formation of talc and biopyriboles (Brearley, 1997). The Allende dark inclusions are crosscut by Ca‐Fe‐pyroxene‐andradite veins and surrounded by Ca‐rich rims that consist of Ca‐Fe‐rich pyroxenes, andradite, wollastonite, and kirschsteinite. Calcium‐rich veins and rims formed after aggregation and lithification of the dark inclusions. The rimmed dark inclusions show zoned depletion in Ca, which is due to a lower abundance of Ca‐Fe‐rich pyroxenes close to the rim. Calcium was probably leached from the inclusions and redeposited along their edges. We infer that the Allende‐like chondrites and dark inclusions experienced similar aqueous alteration to the Bali‐like chondrites and were metamorphosed subsequently, which resulted in loss of aqueous solutions and dehydration of phyllosilicates.We conclude that Ca‐Fe‐rich silicates in the oxidized CV3 chondrites and Allende dark inclusions are secondary and resulted from aqueous fluid‐rock interactions during progressive metamorphism of a heterogeneous mixture of hydrous (ices?) and anhydrous materials; the latter were possibly mineralogically similar to the reduced CV3 chondrites.
Progressive alteration in CV3 chondrites: More evidence for asteroidal alteration
Authors: KROT ALEXANDER N. , PETAEV MICHAEL I. , SCOTT EDWARD R. D. , CHOI BYEON‐GAK , ZOLENSKY MICHAEL E. , KEIL KLAUS 
Published: February 2010

Abstract— The oxidized CV3 chondrites can be divided into two major subgroups or lithologies, Bali‐like (CV3oxB) and Allende‐like (CV3oxA), in which chondrules, calcium‐aluminum‐rich inclusions (CAIs) and matrices show characteristic alteration features (Weisberg et al, 1997; Krot et al, 1997d; Kimura and Ikeda, 1997). The CV3oxB lithology is present in Bali, Kaba, parts of the Mokoia breccia and, possibly, in Grosnaja and Allan Hills (ALH) 85006. It is characterized by the presence of the secondary low‐Ca phyllosilicates (saponite and sodium phlogopite), magnetite, Ni‐rich sulfides, fayalite (Fa>90), Ca‐Fe‐rich pyroxenes (Fs10–50Wo45–50) and andradite. Phyllosilicates replace primary Ca‐rich minerals in chondrules and CAIs, which suggests mobilization of Ca during aqueous alteration. Magnetite nodules are replaced to various degrees by fayalite, Ca‐Fe‐rich pyroxenes and minor andradite. Fayalite veins crosscut fine‐grained rims around chondrules and extend into the matrix. Thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures (<300 °C) in the presence of aqueous solutions. Oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large Δ18Ofayalite‐magnetite fractionation (∼20%). We infer that phyllosilicates, magnetite, fayalite, Ca‐Fe‐rich pyroxenes and andradite formed at relatively low temperatures (<300 °C) by fluid‐rock interaction in an asteroidal environment.Secondary fayalite and phyllosilicates are virtually absent in chondrules and CAIs in the CV3oxA lithology, which is present in Allende and its dark inclusions, Axtell, ALHA81258, ALH 84028, Lewis Cliff (LEW) 86006, and parts of the Mokoia and Vigarano breccias. Instead secondary nepheline, sodalite, and fayalitic olivine are common. Fayalitic olivine in chondrules replaces low‐Ca pyroxenes and rims and veins forsterite grains; it also forms coarse lath‐shaped grains in matrix. Secondary Ca‐Fe‐rich pyroxenes are abundant. We infer that the CV3oxA lithology experienced alteration at higher temperatures than the CV3oxB lithology. The presence of the reduced and CV3oxA lithologies in the Vigarano breccia and CV3oxA and CV3oXB lithologies in the Mokoia breccia indicates that all CV3 chondrites came from one heterogeneously altered asteroid. The metamorphosed clasts in Mokoia (Krot and Hutcheon, 1997) may be rare samples of the hotter interior of the CV asteroid. We conclude that the alteration features observed in the oxidized CV3 chondrites resulted from the fluid‐rock interaction in an asteroid during progressive metamorphism of a heterogeneous mixture of ices and anhydrous materials mineralogically similar to the reduced CV3 chondrites.
An impact‐melt origin for lithology A of martian meteorite Elephant Moraine A79001
Authors: MITTLEFEHLDT David W. , LINDSTROM David J. , LINDSTROM Marilyn M. , MARTINEZ René R. 
Published: February 2010

Abstract— Mixing models using major and trace elements show that the bulk composition of lithology A (xenocryst‐bearing magnesian basalt) of Elephant Moraine A79001 (EETA79001) can be reasonably approximated as a simple mixture of ∼44% EETA79001 lithology B (ferroan basalt) and ∼56% of Allan Hills A77005 (ALHA7705) light lithology (incompatible element‐poor lherzolite). Micro‐instrumental neutron activation analysis (INAA) data on xenocryst‐free groundmass samples of lithology A show that about 20–25% of the melt phase could be dissolved lherzolite. The bulk and groundmass samples of lithology A have excesses in Au, which indicates either meteoritic contamination or addition by some unknown martian geochemical process.Previous workers have suggested that lithology A was formed by either assimilation of cumulates (like ALHA77005), by a basalt (like lithology B), or by mixing of basaltic and lherzolitic magmas. The former scenario is energetically improbable and unlikely to explain the normal Fe/Mg zonation in lithology A groundmass pyroxenes, whereas the latter scenario is unlikely to satisfy the constraints of the mixing model indicating the ultramafic component is poor in incompatible elements. We suggest rather that EETA79001 lithology A is an impact melt composed dominantly of basalt like lithology B and lherzolitic cumulates like the trace‐element‐poor fraction of ALHA77005 or Y‐793605. This model can satisfy the energetic, petrologic, and geochemical constraints imposed by the samples. If EETA79001 lithology A is an impact melt, this would have considerable consequences for current models of martian petrologic evolution. It would call into question the generally accepted age of magmatism of martian basalts and preclude the use of lithology A groundmass as a primary martian basalt composition in experimental studies. Regardless, the latter is required because lithology A groundmass is a hybrid composition.
The composition and thickness of the crust of Mars estimated from rare earth elements and neodymium‐isotopic compositions of Martian meteorites
Authors: NORMAN Marc D. 
Published: February 2010

Abstract— Isotopic and trace element compositions of Martian meteorites show that early differentiation of Mars produced complementary crustal and mantle reservoirs that were sampled by later magmatic events. This paper describes a mass balance model that estimates the rare earth element (REE) content and thickness of the crust of Mars from the compositions of shergottites. The diverse REE and Nd isotopic compositions of shergottites are most easily explained by variable addition of light rare earth element (LREE)–enriched crust to basaltic magmas derived from LREE‐depleted mantle source regions. Antarctic shergottites EET 79001, ALH 77005, LEW 88516, and QUE 94201 all have strongly LREE‐depleted patterns and positive initial 143Nd isotopic compositions, which is consistent with the generation of these magmas from depleted mantle sources and little or no interaction with enriched crust. In contrast, Shergotty and Zagami have negative initial 143Nd isotopic compositions and less pronounced depletions of the LREE, which have been explained by incorporation of enriched crustal components into mantle‐derived magmas (Jones, 1989; Longhi, 1991; Borg et al., 1997).The mass balance model presented here derives the REE composition of the crustal component in Shergotty by assuming it represents a mixture between a mantle‐derived magma similar in composition to EET 79001A and a LREE‐enriched crustal component. The amount of crust in Shergotty is constrained by mixing relations based on Nd‐isotopic compositions, which allows the REE pattern of the crustal component to be calculated by mass balance. The effectiveness of this model is demonstrated by the successful recovery of important characteristics of the Earth's continental crust from terrestrial Columbia River basalts.Self‐consistent results for Nd‐isotopic compositions and REE abundances are obtained if Shergotty contains ∼10–30% of LREE‐enriched crust with >10 ppm Nd. This crustal component would have moderately enriched LREE (Sm/Nd = 0.25–0.27; 147Sm/144Nd = 0.15–0.17; La/Yb = 2.7–3.8), relatively unfractionated heavy rare earth elements (HREE), and no Eu anomaly. Crust with these characteristics can be produced from a primitive lherzolitic Martian mantle by modest amounts (2–8%) of partial melting, and it would have a globally averaged thickness of <45 km, which is consistent with geophysical estimates. Mars may serve as a laboratory to investigate planetary differentiation by extraction of a primary basaltic crust.
Mineralogy, petrography, and thermometry of the H5 chondrite Carcote, Chile
Authors: Kleinschrot Dorothée , Okrusch Martin 
Published: February 2010

Abstract— The Carcote meteorite, detected in 1888 in the northern Chilean Andes, is a brecciated, weakly shocked H5 chondrite. It contains a few barred olivine chondrules and, even more rarely, fan‐shaped or granular orthopyroxene chondrules. The chondrules are situated in a fine‐grained matrix that consists predominantly of olivine and orthopyroxene with accessory clinopyroxene, troilite, chromite, merrillite, and plagioclase. The metal phase is mainly kamacite with subordinate taenite and traces of native Cu. In its bulk rock composition, Carcote compares well with other H5 chondrites so far analysed, except for a distinctly higher C content.Microprobe analyses revealed the following mineral compositions: olivine (Fa16.5–20), orthopyroxene (Fs14–17.5), diopsidic clinopyroxene (FS6–7), plagioclase (An15–20). Troilite is stoichimetric FeS with traces of Ni and Cr; chromite has Cr/(Cr + Al) of 0.86, Fe2+/(Fe2+ + Mg) of 0.80‐0.88 and contains considerable amounts of Ti, Mn, and Zn. Merrillite is close to the theoretical formula Ca18(Mg, Fe)2Na2(PO4)14, although with a Na deficiency not compensated for by excess Ca; the Mg/(Mg + Fe2+) ratio of the Carcote merrilite is 0.93‐0.95. Kamacite and taenite have Ni contents of 5.6–7.2 and 17.1–23.4 wt%, respectively. Native Cu contains about 3.1–3.3 wt% Fe and 1.6 wt% Ni.Application of different geothermometers to the Carcote H5 chondrite yielded apparently inconsistent results. The highest temperature range of 850–950 °C (at 1 bar) is derived from the Ca‐in‐opx thermometer. From the cpx‐opx solvus geothermometers and the two‐pyroxene Fe‐Mg exchange geothermometer, a lower temperature range of 750–840 °C is estimated, whereas lower and more variable temperatures of 630–770 °C are obtained from the Ca‐in‐olivine geothermometer. Recent calibrations of the olivine‐spinel geothermometer yielded a still lower temperature range of 570–670 °C, which fits well to the temperature information derived from the Ni distribution between kamacite and taenite. Judging from crystal chemical considerations, we assume that these different temperatures reflect the closure of different exchange equilibria during cooling of the meteorite parent body.
Evidence for the insignificance of ordinary chondritic material in the asteroid belt
Authors: MEIBOM Anders , CLARK Beth E. 
Published: February 2010

Abstract—We review the meteoritical and astronomical literature to answer the question: What is the evidence for the importance of ordinary chondritic material to the composition of the asteroid belt?From the meteoritical literature, we find that currently (1) our meteorite collections sample at least 135 different asteroids; (2) out of 25+ chondritic meteorite parent bodies, 3 are (by definition) ordinary chondritic; (3) out of 14 chondritic grouplets and unique chondrites, 11 are affiliated with a carbonaceous group/clan of chondrites; (4) out of 24 differentiated groups of meteorites, only the HE iron meteorites clearly formed from ordinary chondritic precursor material; (5) out of 12 differentiated grouplets and unique differentiated meteorites, 8 seem to have had carbonaceous chondritic precursors; (6) a high frequency of carbonaceous clasts in ordinary chondritic breccias suggests that ordinary chondrites have been embedded in a swarm of carbonaceous material. The rare occurrence (only one example) of ordinary chondritic clasts in carbonaceous chondritic breccias indicates that ordinary chondritic material has not been widespread in the asteroid belt; (7) cosmic spherules, micrometeorites, and stratospheric interplanetary dust particles—believed to represent a less biased sampling of asteroidal material—show that only a very small fraction (less than ∼1%) of asteroidal dust has an ordinary chondritic composition. From the astronomical literature, we find that currently (8) spectroscopic surveys of the main asteroid belt are finding more and more nonordinary chondritic primitive material in the inner main belt; (9) the increase in spectroscopic data has increased the inferred mineralogical diversity of main belt asteroids; and (10) no ordinary chondritic asteroids have been directly observed in the main belt.These lines of evidence strongly suggest a scenario in which ordinary chondritic asteroids were never abundant in the main belt. The S‐type asteroids may currently be primarily differentiated, but the precursor material is more likely to have been carbonaceous chondritic, not ordinary chondritic. Historically, carbonaceous material could have dominated the entire main belt. This could explain the presence in the inner main belt of asteroids linked to the primitive carbonaceous chondrites, and the absence of asteroids linked to the ordinary chondrites. The implications of this scenario for the asteroid heating mechanism(s) are briefly discussed.