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The distribution of water in the Moon’s interior carries implications for the origin of the Moon1, the crystallization of the lunar magma ocean2 and the duration of lunar volcanism2. The Chang’e-5 mission returned some of the youngest mare basalt samples reported so far, dated at 2.0 billion years ago (Ga)3, from the northwestern Procellarum KREEP Terrane, providing a probe into the spatiotemporal evolution of lunar water. Here we report the water abundances and hydrogen isotope compositions of apatite and ilmenite-hosted melt inclusions from the Chang’e-5 basalts. We derive a maximum water abundance of 283 ± 22 μg g−1 and a deuterium/hydrogen ratio of (1.06 ± 0.25) × 10–4 for the parent magma. Accounting for low-degree partial melting of the depleted mantle followed by extensive magma fractional crystallization4, we estimate a maximum mantle water abundance of 1–5 μg g−1, suggesting that the Moon’s youngest volcanism was not driven by abundant water in its mantle source. Such a modest water content for the Chang’e-5 basalt mantle source region is at the low end of the range estimated from mare basalts that erupted from around 4.0 Ga to 2.8 Ga (refs. 5,6), suggesting that the mantle source of the Chang’e-5 basalts had become dehydrated by 2.0 Ga through previous melt extraction from the Procellarum KREEP Terrane mantle during prolonged volcanic activity., Water abundance and hydrogen isotope compositions of two-billion-year-old basalt samples returned from the Moon by the Chang’e-5 mission suggest that the samples came from a relatively dry mantle source.

The Moon has a magmatic and thermal history that is distinct from that of the terrestrial planets1. Radioisotope dating of lunar samples suggests that most lunar basaltic magmatism ceased by around 2.9–2.8 billion years ago (Ga)2,3, although younger basalts between 3 Ga and 1 Ga have been suggested by crater-counting chronology, which has large uncertainties owing to the lack of returned samples for calibration4,5. Here we report a precise lead–lead age of 2,030 ± 4 million years ago for basalt clasts returned by the Chang’e-5 mission, and a 238U/204Pb ratio (µ value)6 of about 680 for a source that evolved through two stages of differentiation. This is the youngest crystallization age reported so far for lunar basalts by radiometric dating, extending the duration of lunar volcanism by approximately 800–900 million years. The µ value of the Chang’e-5 basalt mantle source is within the range of low-titanium and high-titanium basalts from Apollo sites (µ value of about 300–1,000), but notably lower than those of potassium, rare-earth elements and phosphorus (KREEP) and high-aluminium basalts7 (µ value of about 2,600–3,700), indicating that the Chang’e-5 basalts were produced by melting of a KREEP-poor source. This age provides a pivotal calibration point for crater-counting chronology in the inner Solar System and provides insight on the volcanic and thermal history of the Moon., Basalt samples returned from the Moon by the Chang’e-5 mission are revealed to be two billion years old by radioisotopic dating, providing insight on the volcanic history of the Moon.

In situ U-Pb radiometric dating of zircons is regarded as one of the most widely used and reliable methods to acquire geochronologic ages. However, it has been recently reported that radiogenic Pb (Pb*) mobilization within zircon may, in some cases, cause inaccurate age determinations with no geological significance. Such Pb* mobilization can be caused by deformation, α-coil damage, fluid-assisted annealing, and recrystallization. In this study, we report an investigation of Pb* mobilization in shock metamorphosed lunar zircons. NanoSIMS (nanoscale secondary ion mass spectrometry) and IMS 1280HR ion microprobe dating, EBSD (electron backscatter diffraction) and CL (cathodoluminescence) mapping, and scanning ion imaging (SII) were applied to micro-zircon grains from the Apollo 72255 Civet Cat norite clast. Based on the large number of grains with similarities in internal zoning, habit and trace element geochemistry, and host mineral context, the Civet Cat norite zircons are interpreted to be primary, igneous grains. The chronology obtained for three consecutive surfaces (at different depths) by NanoSIMS, SII, and IMS 1280HR, respectively, indicates that the radiogenic Pb distribution of the Civet Cat norite zircons is heterogeneous among different polished or sputtering surfaces. Forty-two NanoSIMS U-Pb ages (beam size of 5 μm) are concordant on a Wetherill Concordia diagram, and their corresponding 207Pb/206Pb ages spread from 4015 Ma to 4459 Ma. More notably, the six oldest spots of the 42 define a concordant U-Pb age of 4460 ± 31 Ma (2σ, MSWD = 0.47, P = 0.92) and a weighted mean 207Pb/206Pb age of 4453 ± 34 Ma (MSWD = 0.056, P = 0.998). These dates are among the oldest in the lunar highland rocks. However, the 207Pb/206Pb ages of repolished surfaces of these zircons by IMS 1280HR (beam size of 5 μm) do not reproduce the NanoSIMS results (up to 300 Ma younger). The SII (spatial resolution of 2 μm) confirms a heterogeneous distribution of radiogenic Pb within single grains. The EBSD mapping of these zircon grains shows that they have 3–20° of cumulative lattice misorientation. It is proposed that shock-related deformation has facilitated Pb* migration after primordial crystallization. With currently available data, we cannot preclude the possibility that the large errors of the U-Pb ages obscure reverse discordance that would bias our oldest 207Pb/206Pb ages to older values. Conversely, our data could be explained by mixing of Pb-retention and Pb-loss nanodomains as seen in shocked terrestrial zircon such that U-Pb date of 4460 ± 31 Ma approximates the norite formation.

The South Pole–Aitken (SPA) basin is the oldest and largest impact structure on the Moon, and it gives particular insight on the lunar interior composition1–3. However, the surface of the SPA basin has been substantially modified by consequent impacts and basalt flooding. The exploration of the surficial material and the substructure of the SPA basin is one of the main scientific goals of the Chinese spacecraft Chang’E-4 that landed in the Von Karman crater inside the SPA basin4,5. Here we report the lunar penetrating radar profiles along the track of the lunar rover Yutu-2, which show a three-unit substructure at the landing site. The top unit consists of the ~12-m-thick lunar regolith and ~120 m multilayered ejecta that were delivered from several adjacent craters. The middle unit is the mare basalts filling the Von Karman crater. The lowest unit is another ejecta layer with a thickness of ≥200 m, likely from the Leibnitz crater. These discoveries fully support the local stratigraphy and geological explanation presented previously6. Our results reveal that the surface materials at the Chang’E-4 landing site are unambiguously dominated by the ejecta from the Finsen crater with a minor contribution from other neighbouring craters. The regolith measured by Yutu-2 is representative of the initial lunar deep interior materials, rather than the later erupted basalts. Three different layers can be distinguished in the first 500 metres of depth beneath the South Pole–Aitken basin on the Moon: a first layer made up by regolith and ejecta material from different craters, followed by a middle unit of mare basalts and finally a >200-m-thick layer of ejecta from the Leibnitz crater.

Abstract Zirconolite is a common Zr-rich accessary mineral in mafic rocks. It is also an ideal U–Pb/Pb–Pb chronometer because it commonly contains high U content (mostly 0.1–10 wt%) and negligible initial Pb. However, zirconolite is usually very small (e.g., ~ 1 μm in width) in lunar rocks, requiring a high spatial resolution analysis. We analyzed a single, large (25 μm × 20 μm) grain of zirconolite in lunar meteorite NWA 4485 using Pb–Pb dating by NanoSIMS and U–Th–Pb dating by EPMA. The resultant U–Th–Pb age is 4540 ± 340 Ma (2σ) with a spatial resolution of 1.3 μm. The Pb–Pb age by NanoSIMS is 4348.5 ± 4.8 Ma (2σ) with a spatial resolution of ~ 2 μm, consistent with the age of 4352 ± 10 Ma and 4344 ± 14 Ma reported in the same meteorite and its paired meteorite NWA 4472. Although U–Th–Pb age is somewhat older, it still includes the NanoSIMS results within the analytical uncertainty. This work demonstrates the potential application of the combined EPMA dating and REE analysis of lunar zirconolite, with the benefits of high spatial resolution, non-destructive, and readily accessibility of the instrument. The precision of the EPMA dating (7.6%, 2σ) can be improved by increasing the counting time for Pb, U and Th. We expect to apply this EPMA technique for a quick and non-destructive age survey and geochemical study of zirconolite grains from the lunar mare basalts newly returned by Chang’E-5 mission which landed on a very young (1.2–2.0 Ga by crater-counting chronology) basalt unit in Procellarum KREEP Terrain.

The formation ages of ancient rocks are controversial because of the co-existence of several generations of zircon within a single sample. This study presents BSE imaging, CL imaging, Raman spectroscopy, NanoSIMS trace element imaging and U-Pb dating measurements of zircon from the trondhjemitic enclave and its host leucosome of the Archean Anshan Complex, which were suggested to be the oldest rock (3.8 Ga) in the North China craton. Unlike previous studies, zircon grains were in situ analyzed in polished thin sections instead of mineral separations from the rocks. Three types of zircon have been identified. All zircon in the leucosome share similar morphology and textural relationships observed within thin sections, marked as type I. Zircon in the trondhjemitic enclave can be divided into two groups, marked as type II and type III zircon, respectively. Type II zircons share similar occurrence, texture and U-Pb ages of Type I. They are euhedral prismatic or rhombus in shape with oscillatory zonings. Type I and II zircon yield weighted mean 207Pb/206Pb ages of 3134 ± 34 Ma (n = 14, MSWD = 6.2) and 3132 ± 30 Ma (n = 7, MSWD = 2.1), respectively, which can be referred to as formation ages of the leucosome and the trondhjemitic enclave. Type III zircons generally occur with rounded shapes and core-rim textures. The cores yield ages of 3.7–3.8 Ga, while the rims give discordant ages of 3.3–3.2 Ga, indicating that these zircons are inherited with altered narrow rims during the later magmatism. Therefore, 3.7–3.8 Ga cannot represent the formation age of the trondhjemitic enclave. This study demonstrates that in situ measurements of zircon in polished thin sections can preserve the petrographic settings of zircon and provide strict constraints for the zircon formations and hence the host rocks. More ancient rocks with 3.8 Ga zircon from the Archean Anshan Complex should be studied by this method to further clarify whether there is 3.8 Ga rock in the North China craton.

Apatite, a major hydrous mineral in martian meteorites, has the potential to reveal history of volatiles on Mars. Here we report the H and Cl isotopic systematics of apatite from the enriched basaltic shergottite NWA 8657 to better understand the processes influencing volatiles at or near the martian (sub)surface. The apatite in NWA 8657 has the highest reported δD value (up to 6509 ‰) of any phosphates in martian meteorites. The positive correlation between the H2O contents (72‐2251 ppm) and δD values (3965‐6509 ‰) as well as between the Cl contents (1.28‐6.17 wt%) and δ37Cl values (‐1.7‐4.0 ‰) in NWA 8657 apatite are consistent with mixing between volatiles derived from the martian mantle and meteoric water/fluid. The D‐ and 37Cl‐enrichment of apatite in NWA 8657 implies isotopic exchange with sub‐surficial fluids during post‐crystallization hydrothermal event(s). Plain Language Summary Mars was probably a wet and warm world during its earliest geological history, supported by many lines of evidence. Present‐day Mars is cold and arid although recent remote sensing data support the existence of subsurface glaciers and seasonal fluid activities at some locations. In this study, our aim was to use ground truth about the potential water‐rock interaction on or near‐surface environments on recent Mars via measuring the H and Cl isotopic compositions of apatite from a geologically young meteorite from Mars; the enriched basaltic shergottite NWA 8657. The petrography and mineral chemistry of apatite and other associated phases, e.g., merrillite, maskelynite, mesostasis, and pyroxene, were documented prior to in situ H and Cl isotopes analysis. The water contents of apatite, merrillite, maskelynite, mesostasis, and pyroxene are positively correlated with the δD values. All of the datasets can be reconciled in terms of mixing between two endmembers, a D‐poor (~0 ‰) mantle reservoir and a D‐rich (5920 ± 500 ‰) near‐surface/underground water reservoir. Moreover, apatite in NWA 8657 displays 37Cl‐enriched (~1 ± 1 ‰ in average) characteristics. These signatures are consistent with D‐ and 37Cl‐rich fluid‐assisted isotopic exchange in recent near‐surface environment on Mars.

The temporal duration of lunar evolved magmatism is still poorly constrained. In lunar meteorite NWA 10049, a melt inclusion-bearing zircon fragment provides a new tool to understand the composition and age of the melts from which zircon directly crystallized. The studied zircon-hosted melt inclusions are silica-rich and iron-poor (e.g., ~80–90 wt% SiO2

The Mangui meteorite, also known as the Xishuangbanna meteorite, fell in Menghai, Xishuangbanna Dai Nationality Autonomous Prefecture, Yunnan Province, China at ~9: 45 pm on June 1, 2018. More than 500 fragments of Mangui were collected a total mass of ~50 kg. The mass of the largest fragment is ~1228 g. Mangui has a black fusion crust, a light gray exposure surface, and contains many black shock melt veins and pockets. In this work, the classification of Mingui and its shock history are investigated by studying its petrology, mineral chemistry, and the nature of its shock assemblages. Mangui is mainly composed of olivine, pyroxene, feldspar, Fe-Ni metal, troilite, chromite, merrillite and apatite, showing typical petrologic features of an ordinary chondrite. Relict chondrules are observed in hand specimens but their boundaries are less clear under FE-SEM. Electron Probe Micro Analysis (EPMA) shows that the chemical compositions of olivine (Fa25.1±0.3 mol%( n =71)), low-Ca pyroxene (Fs21.1±0.3Wo1.5±0.2 mol% ( n =58)) and plagioclase Ab84.1±0.7Or7.3±0.4 mol%( n =49)) in Mangui are relatively homogeneous. The petrographic type of Mangui is classified as type 6 by the coarse grains of secondary plagioclase, the homogeneous compositions of olivine and pyroxene, the recrystallization of matrix and blurry boundaries of relict chondrules. The chemical group of Mangui is L based on the average Fa content of olivine (Fe/(Fe+Mg)×100, atomic percentage, 25.1±0.3, n =71) and the average Fs content of pyroxene (Fe/ (Fe+Mg+Ca)×100, atomic percentage, 21.1±0.3, n =58). Therefore, the Mangui meteorite is classified as an L6 ordinary chondrite. The Mangui parent body experienced strong shock metamorphism with the widespread distribution of shock melt veins with widths up to 600 μm. Shock induced melt pockets were also observed. Micron-sized olivine and pyroxene in the center of the shock melt veins display chemical zonation, suggesting that they recrystallized from the shock induced melt. Plagioclase in the shock melt veins has transformed into maskelynite. Two high pressure polymorphs, jadeite and majorite, occur in the shock melt veins and melt pockets as measured by Raman analysis. Jadeite usually displays granular textures in these assemblages as euhedral to sub-euhedral crystals. Majorite was only found in one jadeite assemblage, occurring as inclusions in outer rim of an assemblage. The co-occurrence of majorite and jadeite indicate shock pressures from 17–20 GPa at temperatures ranging from 1900–2000°C. However, ringwoodite, whitlockite and other high pressure polymorphs have not been identified in the shock melt veins pockets. The occurrences of maskelynite, jadeite and majorite, and widespread distribution of shock melt veins and pockets suggest the shock stage of Mangui as S5. The absence of ringwoodite and tuite probably attribute to slow post-shock cooling rates, suggesting that the Mangui parent body experienced strong shock metamorphism with a subsequent slow post-shock cooling history. TEM and XRD work will be performed to better constrain the formation mechanisms of jadeite and majorite and their P - T - t histories. Furthermore, we aim on modelling the impact conditions on the Mangui parent body such as impact velocity, and parent body-impactor sizes by further study of the high-pressure minerals in shock-melt veins of the Mangui meteorite.

Sulfur isotope signatures of Au-bearing pyrite from Lannigou Au deposit, a typical Carlin-type Au deposit in SW China, provide valuable information about the origin of the ore-forming minerals. Analysis by NanoSIMS was used to determine S isotope compositions of Au-bearing pyrite and to map the grain-scale distributions of Au, Cu, As and S in pyrite from the deposit. Based on different textural pattern of pyrites revealed by back-scattered electron (BSE) images, they are divided into three types: Py-1 diagenetic pyrite without core-rim structure, Py-2 pyrite with an Au-free core and a rhythmically-zoned Au-bearing rim, Py-3 Au-bearing pyrite with rhythmic zoning across the entire grain. The element distributions and S isotope compositions of four paragenetic stages are recognized on the basis of textural observation. Py-1 grains and the Au-free homogeneous cores of zoned crystals were formed in Stage 1 while the Au-bearing rims of the zoned crystals with rhythmic zonation of As and Cu, and to a lesser degree Au, were formed in two superimposed stages: stage 2 formed the inner zone that is enriched in As alone; and stage 3 formed the outer zone that is enriched in both Au and As. Other sulfides such as realgar, cinnabar and stibnite are formed in the last stage. The relationship between Au and As distributions in pyrite rim is complicated, changing from coupled to decoupled at the nanoscale. Such complexity is interpreted to reflect fluctuation of fluid composition and temperature with time, which in turn affect the modes of occurrence of As and Au. It is inferred that As mainly occurs in the crystal lattice replacing S whereas Au is mainly present as nanoparticles that were trapped in pyrite during crystal growth. The Au-bearing rims of the zoned pyrite crystals are characterized by highly variable δ34S values from 1.1 to 18.1‰, which exceed the values of the Triassic calcareous host rocks (10–14‰). In contrast, the δ34S values of the Au-free cores of zoned pyrite crystals vary over a narrower interval and are mainly between 6 and 12‰, close to the values of pyrite crystals in the sedimentary country rocks. Our new analyses also reveals that the δ34S values of the Au-bearing fluids generally increase during the formation of the deposit. The observed S isotope variations are consistent with mixing between a magmatic-related fluid with mantle-like δ34S value (∼0‰) and a sedimentary or deep basin brine fluid with elevated δ34S value (>18‰), with an increasing contribution from the latter with time. The notably varied values of δ34S and the disseminations of Au and other trace elements such as As and Cu in pyrite crystals indicate that the process responsible for Au precipitation in this deposit occurred in an open hydrothermal system.

The lunar Mg-suite magmatic rocks are commonly thought to represent mafic intrusions into the anorthositic flotation crust of the lunar magma ocean (LMO). Their geochronology is, therefore, important for constraining evolution models of the LMO. Petrogenetic models of the Mg-suite hold that their parent magmas were derived from primary LMO sources (Mg-cumulates, An-rich plagioclase, and melts enriched in KREEP—potassium, rare earth elements, and phosphorus). Previous radiogenic isotopic age interpretations of Mg-suite and putatively older, related ferroan anorthosites (FANs) overlap over a 200-million-year interval. The Apollo 78238 norite is an exemplary Mg-suite rock, with a relict coarse igneous texture modified by shock metamorphism. In-situ secondary ion mass spectrometry U-Pb analyses of zircon and baddeleyite in 78238 yield discordant arrays, attributed to recent impact metamorphism, with upper intercepts that constrain its crystallization age. The four oldest baddeleyite analyses give a weighted mean 207Pb/206Pb age of 4332 ± 18 Ma (2σ, MSWD = 0.06, P = 0.98), which is interpreted as the crystallization age of the norite. The overlap of the baddeleyite age with previously reported Sm-Nd and Pb-Pb mineral isochron ages for 78238 ( Edmunson et al., 2009 ) supports a moderately fast cooling of the norite. Moreover, it is distinguishably younger than the most precisely dated sample of FAN (Apollo 60025), measured at 4360 ± 3 Ma by Sm-Nd and Pb-Pb mineral isochrons ( Borg et al., 2011 ). Together with the baddeleyite 207Pb/206Pb age of Apollo Mg-suite troctolite 76535 at 4328 ± 8 Ma ( White et al., 2020 ), the chronological record of the 78238 norite indicates a significant Mg-suite magmatic event at 4.33 Ga and a lower age limit on LMO differentiation.

Here we present the isotopic concentrations of He, Ne, Ar, Kr, and Xe for the three Martian meteorites, namely Grove Mountains 99027 (GRV 99027), Northwest Africa 7906 (NWA 7906), and Northwest Africa 7907 (NWA 7907). The cosmic ray exposure (CRE) age for GRV 99027 of 5.7 ± 0.4 Ma (1δ) is consistent with CRE ages for other poikilitic basaltic shergottites and suggests that all were ejected in a single event ~5.6 Ma ago. After correcting for an estimated variable sodium concentration, the CRE ages for NWA 7906 and NWA 7907 of 5.4 ± 0.4 and 4.9 ± 0.4 Ma (1r), respectively, are in good agreement with the CRE age of ~5 Ma favored by Cartwright et al. (2014) for NWA 7034. The data, therefore, support the conclusion that all three basaltic regolith breccias are paired. The ⁴⁰Ar gas retention age for NWA 7907 of ~1.3 Ga is in accord with Cartwright et al. (2014). For NWA 7906, we were unable to determine a ⁴⁰Ar gas retention age. The ⁴He gas retention ages for NWA 7906 and 7907 are in the range of 200 Ma and are much shorter than the ⁴⁰Ar gas retention age of NWA 7907, indicating that about 86–88% of the radiogenic ⁴He has been lost. The Kr and Xe isotopic concentrations in GRV 99027 are composed almost exclusively of Martian interior (MI) gases, while for NWA 7906 and NWA 7907, they indicate gases from the MI, elementally fractionated air, and possibly Martian atmosphere.

Aluminum-rich (Al2O3 > 10 wt%) chondrules (ARCs) are important chondritic components that petrologically link two other major chondritic components, ferromagnesian chondrules (FMCs) and calcium-aluminum-rich inclusions (CAIs), which formed in different regions of the protoplanetary disk. They are closely related to FMCs as indicated by their similar igneous textures, mineral assemblages, and Al-Mg isotope systematics; meanwhile, they have genetic a relationship with CAIs as indicated by their distinctly Al2O3-rich compositions and occasional occurrences of relict CAI minerals. In order to further understand their formation mechanism and genetic relationships to FMCs and CAIs, nine ARCs and three ARC-related objects from Allende (CV3 oxidized), Leoville (CV3 reduced), and the ungrouped Ningqiang carbonaceous chondrites were studied for petrology, mineralogy, bulk compositions, rare earth element (REE) abundances, and in situ oxygen isotopic compositions. Our results suggest that (i) ARCs crystallized from incompletely molten droplets with crystallization sequences mainly determined based on their bulk compositions. Projection of their bulk compositions onto the forsterite-saturated tridymite-diopside-spinel diagram allows us to classify them into Al-rich [Sp], Al-rich [En], and Al-rich [Plag]; (ii) ARC precursors are mixtures of refractory materials and the precursors of FMCs, in which the refractory materials have diverse sources rather than a single type of CAI/AOA (amoeboid olivine aggregate); this is inferred from the bulk compositions, relict minerals (both coarse- and fine-grained spinel, olivine, and Al-Ti-diopside), and various CAI-like REE patterns (unfractionated Group I/III and highly fractionated Group II/II-like) of ARCs. The sources include AOAs and igneous Type B/C CAIs; (iii) ARCs were melted in the FMC-forming region, possibly by the same heating mechanism or during the same transient heating event, which is consistent with the similar oxygen isotopic compositions of their phenocrysts (Δ17O = −5.2 ± 1.7‰, 2SD). Thus, we consider that ARCs formed by melting of mixtures of diverse refractory components with the FMC precursors in the FMC-forming region.

We report an imaging method of zircon U-Pb dating with NanoSIMS 50L, which overcomes the significant U-Pb fractionation as the pit was sputtered deeper during conventional spot mode analysis and can be applied to irregular small grains or heterogeneous areas of zircon. The U-Pb and Pb-Pb ages can be acquired simultaneously for 2 μm×2 μm (for small grains) or 1 μm×9 μm (for zoned grains), together with Zr, Y and other trace elements distributions. Using zircon M257 as standard, the U-Pb ages of other zircon standards, including Qinghu, Plesovice, Temora and 91500, were measured to (2σ) as 158.8±0.8, 335.9±3.4, 412.0±12 and 1067±12 Ma, respectively, consistent with the recommended values within the analytical uncertainties. Tiny zircon grains in the impact melt breccia of the lunar meteorite SaU 169 were also measured in this study, with a Pb-Pb age of 3912±14 Ma and a U-Pb age of 3917±17 Ma, similar to previous results reported for the same meteorite. The imaging method was also applied to determine U-Pb age of the thin overgrowth rims of Longtan metamorphic zircon, with a Pb-Pb age of 1933±27 Ma and a U-Pb age of 1935±25 Ma, clearly distinct from the Pb-Pb age of 2098±61 Ma and the U-Pb age of 2054±40 Ma for detrital cores.

The Almahata Sitta MS-170 ureilite (a piece of a breccia originating from the asteroid, 2008 TC3) consists mainly of olivine, with many diamond and graphite grains existing between the olivine grains. The occurrences of the diamonds are unique; i.e., (i) some diamonds exhibit sub-euhedral habits and (ii) some diamonds have large grain-size (up to about 40 mu m). Several diamonds are segmented into many fragments by fractures. Individual fragments have similar crystallographic orientation, which implies that the adjacent diamond segments were originally a single crystal. Large diamond assemblages occur besides such individual diamond grains. In one of the largest assemblages (almost about 100 mu m in size) has also the same crystallographic orientation. They can be regarded as the pieces of a previously unique single diamond, which provides evidence for large single-crystals diamond in meteorites. Almahata Sitta MS-170 is a meteorite fragment from the 2008 TC3 asteroid that underwent less shock than other ureilitic meteorites. It is unlikely that such large diamonds were formed from graphite through a shock-induced phase transformation during planetesimal collision, despite this idea being now widely accepted as the diamond formation mechanism of ureilites. Fine-scale heterogeneous distribution of impurities (hydrogen, nitrogen, and oxygen) exists in single crystal diamonds, indicative of sluggish growth. This distribution is reminiscent of sector zoning growth. Its grain size, the shock features of MS-170, and the C- and N-isotopic composition signatures allow us to revive classical and but not widely accepted models for diamond formation in ureilites; i.e., a diamond formed from partially melted magma or a C-O-H fluid in the deep interior of the ureilite parent-body or, alternatively, through a chemical vapor deposition (CVD) process in the solar nebula. Considering present mineralogical and isotopic features, the former scenario is more favorable. (C) 2015 Elsevier Ltd. All rights reserved.

International audience; Mineral inventories of enstatite chondrites; (EH and EL) are strictly dictated by combined parameters mainly very low dual oxygen (fO2) and sulfur (fS2) fugacities. They are best preserved in the Almahata Sitta MS-17, MS-177 fragments, and the ALHA 77295 and MAC 88136 Antarctic meteorites. These conditions induce a stark change of the geochemical behavior of nominally lithophile elements to chalcophile or even siderophile and changes in the elemental partitioning thus leading to formation of unusual mineral assemblages with high abundance of exotic sulfide species and enrichment in the metallic alloys, for example, silicides and phosphides. Origin and mode of formation of these exotic chondrites, and their parental source regions could be best scrutinized by multitask research experiments of the most primitive members covering mineralogical, petrological, cosmochemical, and indispensably short-lived isotopic chronology. The magnitude of temperature and pressure prevailed during their formation in their source regions could eventually be reasonably estimated: pre- and postaccretionary could eventually be deduced. The dual low fugacities are regulated by the carbon to oxygen ratios estimated to be >0.83 and

Martian meteorites of various petrogeneses retain a record of volatiles on Mars: from the hydrosphere, crustal water to the mantle. Sputtering of the martian atmosphere by solar wind after the loss of Mars' magnetic field enriched it in deuterium, which exchanged with martian crustal water. Recent studies show that the hydrogen isotopic composition of the martian crustal water reservoir varies from 3000 to 7000‰ but requires better constraints. Melt inclusion glasses, maskelynite and fusion crust from the depleted olivine-phyric shergotite NWA 6162 were analyzed using NanoSIMS, providing a unique insight into the hydrogen isotopic and volatile elemental content of both the martian crustal water reservoir and the mantle source. The H2O, S, and Cl contents of the melt inclusion glasses are ∼0-3137, 14-239, and 16-967 ppm, respectively. δD values vary from −560 to 6137‰. The water content positively correlates with the δD values in both the melt inclusion glasses and maskelynite in a two end-member mixing trend. One end-member is the magmatic water with a δD value of ∼0‰, and the other end member is the martian crustal water with δD ranging from 5000 to 6000‰. NWA 6162, a depleted olivine-phyric shergottite, originated from a different mantle source to the enriched lherzolitic shergottites. However, both types of shergottites exchanged with martian crustal water with the same δD values, indicating a homogeneous martian crustal water hydrogen isotopic composition (5000-6000‰). Most melt inclusion glasses from NWA 6162 have low water content (0-234 ppm) except for two enriched locations as micron-sized bands and dendrites. The low water content in most melt inclusion glasses, the dendritic shaped water enriched areas in melt inclusions, and the martian crustal water diffusion profile recorded in maskelynite collectively suggest short-lived water-rock interactions in the NWA 6162 parent rock that was probably induced by impact. Furthermore, a great contribution (up to 98%) of surface Cl accompanying D-enriched water was recorded in the melt inclusions supported by the positive correlation between Cl and H2O. The presence of sulfide and S-rich hot spots and low δD end-member of the magmatic water indicate that the degassing during post-entrapment crystallization and ascent of the melt inclusion is negligible. H2O, S, and Cl contents of the martian mantle reservoir are estimated to be 0.1-3, 0.5-15, and 0.5-4 ppm respectively, after the correction of fractional crystallization of the melt inclusions and contribution from the martian surface reservoir. The martian mantle reservoir estimated from NWA 6162 was water-, S-, and Cl-poorer than the Earth's interior.

Two petrographic settings of carbonaceous components, mainly filling open fractures and occasionally enclosed in shock-melt veins, were found in the recently fallen Tissint Martian meteorite. The presence in shock-melt veins and the deuterium enrichments (delta D up to +1183 parts per thousand) of these components clearly indicate a pristine Martian origin. The carbonaceous components are kerogen-like, based on micro-Raman spectra and multielemental ratios, and were probably deposited from fluids in shock-induced fractures in the parent rock of Tissint. After precipitation of the organic matter, the rock experienced another severe shock event, producing the melt veins that encapsulated a part of the organic matter. The C isotopic compositions of the organic matter (delta C-13 = -12.8 to -33.1 parts per thousand) are significantly lighter than Martian atmospheric CO2 and carbonate, providing a tantalizing hint for a possible biotic process. Alternatively, the organic matter could be derived from carbonaceous chondrites, as insoluble organic matter from the latter has similar chemical and isotopic compositions. The presence of organic-rich fluids that infiltrated rocks near the surface of Mars has significant implications for the study of Martian paleoenvironment and perhaps to search for possible ancient biological activities on Mars.

We measured the hydrogen isotopes and water contents of melt inclusions and apatite that locate far from shock-induced melt veins in the Martian meteorite GRV 020090, using nano-scale secondary ion mass spectrometry (nanoSIMS). The melt inclusions in olivine show hydration profiles, with both the water contents and the δD values increasing from the cores (2σ) (170 ± 7 ppm and 3386 ± 126‰) to the rims (5337 ± 200 ppm and 5519 ± 65‰). The extremely high δD values of the melt inclusions relative to a maximum of 4239 ± 81‰ of apatite that crystallized from the last residual melt convincingly argue that the observed hydration postdated emplacement of the parent magma of GRV 020090. This is also a robust line of evidence for past-presence of liquid water on Mars. Diffusion simulation of the hydration profiles of both water contents and δD values constrains the duration of liquid water up to 130,000–250,000 years at 0 °C or 700–1,500 years at 40 °C. All analyses of the melt inclusions, including the hydration profiles, show a logarithmic correlation between the water contents and the δD values, plotting within a two-endmember mixing area. The extremely D-enriched endmember represents Martian underground water, with a δD value of 6034 ± 72‰ (2σ). This is the highest δD value reported in Martian meteorites and it is consistent with the recent analyses of Martian soils by the Curiosity rover ( Leshin et al., 2013 ), suggestive of more water escaped from Mars than previous estimates. The analyses of apatite show a distinct positive correlation between the water contents (0.10–0.58 wt%) and the δD values (737–4239‰), which can be explained by assimilation of D-rich Martian crustal materials and enhancement of water via fractional crystallization. The observed correlation suggests that the water contents of Martian mantle reservoirs might have been overestimated from D-enriched apatite in previous studies. Our estimation based on the least contaminated apatite grains from GRV 020090 turned out a low water content of the primordial parent magma (380–750 ppm), which was likely derived from a relatively dry Martian mantle reservoir of GRV 020090 (∼38–75 ppm H2O).

–The Sutter’s Mill (SM) carbonaceous chondrite is a regolith breccia, composedpredominantly of CM2 clasts with varying degrees of aqueous alteration and thermalmetamorphism. An investigation of presolar grains in four Sutter’s Mill sections, SM43,SM51, SM2-4, and SM18, was carried out using NanoSIMS ion mapping technique. A totalof 37 C-anomalous grains and one O-anomalous grain have been identified, indicating anabundance of 63 ppm for presolar C-anomalous grains and 2 ppm for presolar oxides.Thirty-one silicon carbide (SiC), five carbonaceous grains, and one Al-oxide (Al 2 O 3 ) wereconfirmed based on their elemental compositions determined by C-N-Si and O-Si-Mg-Alisotopic measurements. The overall abundance of SiC grains in Sutter’s Mill (55 ppm) isconsistent with those in other CM chondrites. The absence of presolar silicates in Sutter’sMill suggests that they were destroyed by aqueous alteration on the parent asteroid.Furthermore, SM2-4 shows heterogeneous distributions of presolar SiC grains (12–54 ppm)in different matrix areas, indicating that the fine-grained matrix clasts come from differentsources, with various thermal histories, in the solar nebula.INTRODUCTIONThe Sutter’s Mill (SM) carbonaceous chondrite(CM2) fell in California on April 22, 2012. WeatherDoppler radars detected the falling meteorites, resultingin a fast recovery of some stones (Fries and Fries 2010;Jenniskens et al. 2012). The first stones found (SM 1-3)were recovered before rain and have minimal terrestrialweathering. Petrographic studies indicate that Sutter’sMill is a regolith breccia, composed of CM2 lithologieswith various degrees of aqueous alteration and thermalmetamorphism (Jenniskens et al. 2012; Zolensky et al.2012). Previous studies of acid residues show that someCM2 chondrites (e.g., Murchison, Murray) containabundant presolar material, mainly presolar SiC grains(e.g., Zinner 2013). Sutter’s Mill contains abundant fine-grained matrix areas, which are suitable for presolargrain searches. Previous studies have suggested thatdifferent secondary processes (aqueous alteration,thermal metamorphism) may preferentially destroypresolar mineral phases (presolar silicate/oxide, SiC)(e.g., Huss et al. 2003; Floss and Stadermann 2012).Here, we used NanoSIMS ion imaging to investigate thepresolar inventories of different SM fragments, forcomparison with the presolar grain abundances inMurchison and other primitive chondrites, and to gaina better understanding of the effects of secondaryprocesses on the preservation of presolar grains.SAMPLES AND EXPERIMENTALThe fragments analyzed in this study are SM43,SM51, SM2-4 (a subsample of SM2), and SM18 (forthe find locations in the strewn field, see Jenniskens

In the impact melt breccia (IMB) of Sayh al Uhaymir (SaU) 169, the most KREEP-rich lunar meteorite to date ( Gnos et al., 2004 ), clasts of a new type of lithologies were discovered, consisting of Ca-poor and Ca-rich pyroxenes (60.8 vol.%), Ba-rich K-feldspar (27.9 vol.%), phosphates (5.6 vol.%), Nb-rich ilmenite (4.0 vol.%), zircon (1.2 vol.%) and minor sulfide (0.6 vol.%). These mafic lithic clasts are more enriched in KREEP component (∼1500 × CI) than the host meteorite and are highly enriched in potassium. They are referred to as very high-K (VHK) KREEP lithology, and probably most close to the last residual liquid of the Lunar Magma Ocean without significant dilution by other Mg-rich magmas. The fine-grained matrix of the SaU 169 IMB has very similar mineral chemistry to the VHK KREEP lithology, but contains abundant plagioclase with trace K-feldspar. The matrix shows decoupling of K from the REEP-like component; however, it cannot be simply interpreted by mixing the VHK KREEP lithology with anorthosites, which should have diluted the REEP-like component with the same proportion. SIMS Pb–Pb dating was conducted on zircons in various petrographic settings and with different crystal habits. All analyses show a main age peak at 3921 ± 3 Ma and a smaller one at 4016 ± 6 Ma. The main age peak is identical to the previous Pb–Pb age by Gnos et al. (2006) and U–Pb age by Liu et al. (2009) , dating the catastrophic shock event contributed to the formation of SaU 169 IMB. The older ages are consistent with the previous report of an older bulk U–Pb age by Kramers et al. (2007) , suggestive of presence of relict crystals in a few large zircon grains. The VHK KREEP clasts predated the fine-grained matrix, but have the same zircon Pb–Pb ages as the latter within the analytical uncertainties. Plagioclase was converted to maskelynite whereas zircon was shocked to diaplectic glass, probably by a second event at ∼2.8 Ga. However, the identical zircon Pb–Pb ages of the amorphous parts and the remained crystalline areas indicate no resetting of Pb–Pb isotopes by the later shock metamorphism, or there was another severe impact event postdated solidification of the fine-grained matrix within a few million years.

– Rb-Sr and Sm-Nd isotopic analyses of the lherzolitic shergottite Grove Mountains (GRV) 99027 are reported. GRV 99027 yields a Rb-Sr mineral isochron age of 177 ± 5 (2σ) Ma and an initial 87Sr/86Sr ratio (ISr) of 0.710364 ± 11 (2σ). Due to larger uncertainties of the Sm-Nd isotopic data, no Sm-Nd isochron age was obtained for GRV 99027. The e143Nd value is estimated approximately +12.2, assuming an age of 177 Ma. The ISr of GRV 99027 is distinguishable from other lherzolitic shergottites, confirming our previous conclusion that it is not paired with them (Lin et al. 2005). The new data of GRV 99027 support the same age of approximately 180 Ma for most lherzolitic shergottites, and fill the small gap of ISr between Allan Hills A77005 and Lewis Cliff 88516 (Borg et al. 2002). All available data are consistent with a single igneous source for the intermediate subgroup of lherzolitic shergottites.

Polynuclear aromatic hydrocarbons (PAHs) and black carbon (BC) in sediments are powerful tools in the identification of the combustion process throughout geologic history. In this study, combustion-derived PAHs and BC were carefully investigated in sediments from the Global Stratotype Section and Point of the Permian–Triassic (P/Tr) boundary in Meishan, China. Quantitative analyses of combustion-derived PAHs and BC demonstrate anomalously high concentrations in the boundary event beds that coincide with the mass extinction horizon. The prevalence of parent polynuclear aromatics (e.g., phenanthrene) in PAHs, together with non-metric multidimensional scaling analysis, confirms that the PAHs are mainly derived from vegetation burning instead of having a coal and/or oil origin. BC detected in sediment occurs in various forms from large irregular charcoal particles to fine aciniform soot, with an equivalent reflectance of up to 3.5%. The results strongly suggest that a wildfire occurred during the P/Tr boundary, which served as one of the possible triggers of mass extinction on land. The wildfire occurrence indicates that the O2 concentration of the atmosphere during (or before) the P/Tr mass extinction was probably >17%. The temporal coincidence of the mass extinction with intensive volcanic eruption, marine anoxia and wildfire events in the region of the Meishan section provides new insight into the mechanisms of the P/Tr biotic crisis. Our results show that wildfires could have played an important role in the collapse of the ecosystem in the Meishan P/Tr events.

We report the concentration of 50 elements, including rare earth elements (REEs) and platinum group elements (PGEs) in bulk samples of the Grove Mountains (GRV) 99027 lherzolitic shergottite. The abundances of REEs are distinctly lower than those of Allan Hills (ALH) A77005 and other lherzolitic shergottites, indicating that GRV 99027 is not paired with them. It may, nevertheless, sample the same igneous unit as the others (Lin et al. 2005b; Wang and Chen 2006). The CI- normalized elemental pattern of GRV 99027 reveals low (0.004-0.008 × CI) and unfractionated PGEs (except for Pd of 0.018 × CI) without depletion of W or Ga relative to lithophile element trends. Fractionation between siderophile and lithophile elements become less pronounced with increase of volatility, except for high abundances of Ni and Co. These characteristics are probably representative of the mantle of Mars, which is consistent with previous work that the Martian mantle formed in a deep magma ocean followed by a later accretion of chondritic materials.

Petrography and mineral chemistry of two new ureilites, GRV 021512 and 022931, from the Grove Mountains, Antarctica, are reported in this paper. GRV 021512 exhibits a typical ureilite texture, and consists of 48.3% olivine, 9.4% pigeonite and 38.1% carbonaceous interstitial material and/or reduction product. GRV 022931 has a cataclastic porphyritic texture, and consists of 19.1% olivine and 14.1% pigeonite embedded in 66.3% carbonaceous interstitial material and/or reduction product. The coarse-grained olivine and pigeonite in both meteorites have homogeneous cores, and they are FeO-rich within the range of the ferroan subgroup (subgroup I) of olivine-pigeonite ureilites. All olivine grains of the meteorites show reduction zones along boundaries and cracks. Abundant diamond coexists with graphite as graphite-rich patches and veins in the carbonaceous interstitial material. Petrogenesis of both meteorites and the origin of diamond are discussed.

Permian–Triassic boundary sections record the most severe mass extinction event in geological history. However, there is a long-standing controversy of whether bolide impact and/or basaltic flood volcanism triggered the mass extinction. Platinum-group elements (PGEs) are enriched in most extraterrestrial materials, but highly depleted in the terrestrial crust materials. We analyzed Ir, Ru, Rh, Pt and Pd in a set of samples from the global stratotype section and point (GSSP) of the Permian–Triassic boundary at Meishan, China, using isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) and nickel sulfide fire assay (NiS-FA) combined with Te coprecipitation. The samples have no Ir anomaly (5–53 pg/g), and their PGE patterns normalized to chondrites are highly fractionated with Ir/Pd ratios of 0.02–0.03 × CI, distinct from most extraterrestrial materials. In contrast, these patterns are closely parallel to those of the Siberian and probably Emeishan flood basalts, suggestive of possible sources of PGEs from the basalts. The abundances of PGEs increase in order of the pyrite lamina on the top of bed 24, bed 25 and bed 26, and then decrease to bed 28, probably indicative of a maximum eruption of the flood basalts during deposition of bed 26. The new data favor massive volcanism, rather than extraterrestrial impact, as a major cause of the Permian–Triassic boundary mass extinction.

Significance After the Apollo and Luna missions, which were flown about 40 years ago, the Moon was explored only from orbit. In addition, no samples were returned from the young and high-FeO and TiO 2 mare basalt in the northern Imbrium basin. Such samples are important to understand the formation and evolution of the Procellarum KREEP [potassium (K), rare earth elements (REE), and phosphorus (P)] terrain, a key terrain highly enriched in radioactive nuclides. The Chang’e-3 mission carried out the first in situ analyses of chemical and mineral compositions of the lunar soil and ground-based measurements of the lunar regolith and the underlying basalt units at this specific site. The lunar regolith layer recorded the surface processes of the Moon, whereas the basalt units recorded the volcanic eruption history.

Twenty-four refractory inclusions (40-230 μm, with average of 86 ± 40 μm) were found by X-ray mapping of 18 ordinary chondrites. All inclusions are heavily altered, consisting of finegrained feldspathoids, spinel, and Ca-pyroxene with minor ilmenite. The presence of feldspathoids and lack of melilite are due to alteration that took place under oxidizing conditions as indicated by FeO-ZnO-rich spinel and ilmenite. The pre-altered mineral assemblages are dominated by two types: one rich in melilite, referred to as type A-like, and the other rich in spinel, referred to as spinel-pyroxene inclusions. This study and previous data show similar type and size distributions of refractory inclusions in ordinary and enstatite chondrites. A survey of refractory inclusions was also conducted on Allende and Murchison in order to make unbiased comparison with their counterparts in other chondrites. The predominant inclusions are type A and spinel-pyroxene, with average sizes of 170 ± 130 μm (except for two mm-sized inclusions) in Allende and 150 ± 100 μm in Murchison. The relatively larger sizes are partially due to common conglomerating of smaller nodules in both chondrites. The survey reveals closely similar type and size distributions of refractory inclusions in various chondrites, consistent with our previous data of other carbonaceous chondrites. The petrographic observations suggest that refractory inclusions in various groups of chondrites had primarily formed under similar processes and conditions, and were transported to different chondrite-accreting regions. Heterogeneous abundance and distinct alteration assemblages of refractory inclusions from various chondrites could be contributed to transporting processes and secondary reactions under different conditions.

We report petrography, mineral chemistry, and microdistribution of rare earth elements (REE) in a new lherzolitic shergottite, Grove Mountains (GRV) 99027. The textural relationship and REE patterns of minerals suggest precipitation of cumulus olivine and chromite, followed by equilibrium crystallization of a closed system with a bulk composition of the inferred intercumulus melt. Subsolidus equilibrium temperatures of pyroxenes and olivine range from 1100 to 1210 °C, based on a two-pyroxene thermometry and Ca partitioning between augite and olivine. Oxygen fugacity of the parent magma is 1.5–2.5 (av. 2.0 ± 0.4) log units below the quartz-fayalite-magnetite (QFM) buffer at 960–1360 °C, according to the olivine-orthopyroxene-chromite barometer. The ilmenite-chromite barometer and thermometer show much wider ranges of oxygen fugacity (1.0–7.0 log unit below QFM) and temperature (1130–480 °C), suggesting subsolidus equilibration of the oxides at low temperatures, probably due to deep burial of GRV 99027 on Mars. The low oxygen fugacity and LREE depletion of the parent magma of GRV 99027 suggest low contamination by martian crust. Characteristics of GRV 99027 demonstrate similarity of lherzolitic shergottites, suggesting a high possibility of launch pairing or a homogeneous upper mantle of Mars if they were ejected by individual impact events. However, GRV 99027 probably experienced severe post-shock thermal metamorphism in comparison with other lherzolitic shergottites, based on the re-crystallization of maskelynite, the homogeneity of minerals, and the low subsolidus equilibrium temperatures between chromite and ilmenite.

Sixty-eight refractory inclusions and fragments were found in two polished thin sections of the Sahara 97159 EH3 chondrite, indicative of the highest abundance of refractory inclusions (22/cm2, or 0.06 vol.%) in enstatite chondrites studied to date. All of the inclusions are intensely altered, mainly producing feldspathoids and albite, CaO depletion and minor Ti-rich compounds, such as Ti-sulfides. The alteration assemblages and FeO-poor spinel suggest that the reactions took place under reducing and SiO2-rich conditions. This is consistent with the redox state of the host enstatite chondrite. The presence of Ti sulfides and low FeO alteration phases distinguishes alteration of E chondrite refractory inclusions from that of carbonaceous and ordinary chondrites. Most of the inclusions are referred to as Type A–like (35) and spinel-rich (26), respectively. Assuming melilite has been altered, these inclusions could be analogues of individual concentrically zoned objects of fluffy melilite-spinel-rich (Type A) and spinel-pyroxene-rich inclusions from carbonaceous chondrites such as the Ningqiang (CV anomalous) and Y 81020 (CO3) chondrites. Two inclusions consist mainly of Ca-pyroxene, fine-grained alteration products (feldspathoids and albite) and spinel. They are probably altered fragments of Ca-pyroxene-plagioclase-rich (Type C) inclusions, assuming all plagioclase has been altered to produce the fine-grained groundmass. Five other inclusions are hibonite and/or corundum bearing, similar to those reported in carbonaceous chondrites. Abundance ratios of various types of the inclusions from Sahara 97159 are similar to those from Ningqiang and Y 81020. Most of the observations, including mineral assemblages, mineral chemistry, texture, bulk compositions, O isotopic compositions and REE patterns, of the Sahara inclusions suggest a common reservoir of refractory inclusions in enstatite, ordinary and carbonaceous chondrites. The apparent differences, such as absence of melilite and anorthite, rare Wark-Lovering rim and small size, can be explained by intense alteration due to large change of postformation environment of these inclusions, size sorting and collision during transfer. Hence, these differences are not inconsistent with the common reservoir model. Refractory inclusions in non-carbonaceous chondrites may put additional constraints on origins of refractory inclusions, and provide hints for a spatial relationship of their host meteorites.

We determined the mineralogical and chemical characteristics and the He, Ne, and Ar isotopic abundances of 2 meteorites that fell in China and of 2 meteorites that were recovered by the 15th Chinese Antarctic Research Expedition. Guangmingshan (H5), Zhuanghe (H5), and Grove Mountain (GRV) 98002 (L5) yield cosmic ray exposure (CRE) ages of 68.7 ± 10.0 Ma, 3.8 ± 0.6 Ma, and 17.0 ± 2.5 Ma, respectively. These ages are within the range typically observed for the respective meteorite types. GRV 98004 (H5) had an extremely short parent body-Earth transfer time of 0.052 ± 0.008 Ma. Its petrography and mineral chemistry are indistinguishable from other typical H5 chondrites. Only 3 other meteorites exist with similarly low CRE ages: Farmington (L5), Galim (LL6), and ALH 82100 (CM2). We show that several asteroids in Earth-crossing orbits, or in the main asteroid belt with orbits close to an ejection resonance, are spectrally matching candidates and may represent immediate precursor bodies of meteorites with CRE ages ≤0.1 Ma.

We report the petrography, mineral chemistry and oxygen isotopic composition of GRV 99027, a new Martian meteorite recently collected during the 16th Chinese Antarctic Research Expedition. This meteorite consists of two textural regions. The interstitial region is characterized by the presence of plagioclase and phosphate, and higher FeO contents of olivine and orthopyroxene, in comparison with the poikilitic region. All of the observations are similar to the three known Martian lherzolites. We classify GRV 99027 as the fourth sample of Martian lherzolite.

Twenty-eight meteorites were collected on blue ice in the Grove Mountains region, Antarctica, by the 16th Chinese Antarctic Research Expedition (CHINARE). 26 out of the stones are ordinary chondrites, and their chemical-petrographic types are assigned based on electron probe microanalyses, petrography and mineralogy. 6 of them are unequilibrated L-chondrites, and the other 20 chondrites are equilibrated, including 6 H-group (3 H4, 1 H5 and 2 H6), 9 L-group (3 L4, 1 L5 and 5 L6) and 5 LL-group (2 LL4 and 3 LL5). Detailed comparative study suggests that 10 of them (including other 2 chondrites collected by the 15th CHINARE) could be paired, and represent 5 individual fall events. Hence, all 32 meteorites collected from the Grove Mountains probably belong to 27 fall events, suggestive of meteorite transferring and concentrating processes. The Grove Mountains are likely a new meteorite-enriched region. Distribution patterns of chemical-petrographic type and mass of the Grove Mountains meteorites are significantly distinct from those found in other regions, indicative of their unique sources and/or concentration mechanism. However, more studies are required in order to clarify these differences.

EET 90102 is the first known diopside-bearing EL6 chondrite. Diopside occurs in most aubrites and is occasionally found as rare small grains in unequilibrated enstatite chondrites, but is unknown from equilibrated enstatite chondrites. We have carried out a study of the rare earth element (REE) distributions in EET 90102, with a specific emphasis on diopside, in order to better understand its origin in this meteorite. We also present data for Ca-rich pyroxenes from two unequilibrated (EH3) enstatite chondrites for comparison. Our data show that diopside and other silicates in EET 90102 exhibit volatility-related anomalies indicative of formation under highly reducing conditions. Such anomalies have not previously been observed in EL6 chondrites, although they are common in unequilibrated enstatite chondrites. Diopside in EET 90102 probably formed by metamorphic equilibration of enstatite and oldhamite. The REE compositions of some grains, in particular the presence of positive Yb anomalies, indicate that they inherited their REE characteristics largely from CaS. Other grains have REE patterns that are more consistent with a derivation of diopside primarily from enstatite. In contrast to other EL6 chondrites, which experienced slow cooling, EET 90102 was quenched from high metamorphic temperatures. Thus, there may have been insufficient time to completely homogenize diopside REE compositions. The presence of diopside in EET 90102 simplifies one outstanding problem of aubrite formation. Melting of a diopside-bearing enstatite chondrite protolith provides a source for the abundant diopside in aubrites without requiring the oxidation of oldhamite, as suggested by previous research.

Two Type B refractory inclusions, consisting mainly of melilite, fassaite and spinel ± anorthite, were found in the anomalous Ningqiang carbonaceous chondrite. The composition of melilite varies from Ak4–15 near the diopside rims to Ak80–90 in the centers of these inclusions. In addition, melilite exhibits intergrowths with fassaite and/or anorthite in the centers of the inclusions. These observations suggest that both inclusions were once molten. The Na2O content of melilite is positively correlated with the Ak content for Ak Beyond crystallization from melts, the Ningqiang Type B refractory inclusions contain possible relict fassaite fragments. These fragments are embedded in gehlenitic melilite and have corroded outlines surrounded by highly TiO2-enriched fringes, as distinguished from the fassaites intergrown with melilite in the centers of the inclusions. In inclusion NQJ331, most grains of anorthite occur as irregular coarse-grained fragments, distinct from those intergrown with melilite. Toward these anorthite fragments, melilite shows a steep decrease in Ak content. We propose that these anorthite fragments are xenoliths and were probably injected into the host while the latter was crystallizing. Palisades occur only in NQJ331, and are probably relicts too. Distinctly low V2O3 concentrations of the spinels from the palisade bodies and the presence of palisade bodies consisting of one or more corroded crystals of fassaite ± anorthite are new lines of the evidence for a relict origin of palisades. The other Type B refractory inclusion, NQJ354, contains a spherule consisting of a grossite core and a spinel mantle enclosing laths of hibonite. The modal abundance and mineral chemistry of the spinel-hibonite spherule are distinctly different from the host inclusion. We propose that the spinel-hibonite spherule crystallized from a SiO2-poor melt at a very high temperature and was injected into the Type B host before the latter was completely solidified. This grossite-bearing spinel-hibonite spherule may be related to the spinel-hibonite spherules in CM2 chondrites.

Petrography and mineral chemistry of Ca, Al-rich inclusions of Ningqiang carbonaceous chondrite are studied and the highly Re-Os fractionated Pt-metal nuggets in it is discovered. The refractory inclusions are classified into melilite-spinel-rich, and spinel-pyroxene-rich types. The former probably crystallized from melts, while the latter could be aggregates of the nebular condensates. The strong fractionation between Re and Os suggests a pro-solar origin of the Pt-metal nuggets, which probably experienced various processes of formation and evolution before being captured by the refractory inclusions as indicated by the depletions of W and Mo.

In three polished thin sections of Yamato 791717 (CO3). fifty-five Ca, Al-rich inclusions were found, which include two hibonite-bearing, eight melilite-rich and forty-five spinel-pyroxene inclusions. Based on the petrography and mineral chemistry of the inclusions, it is proposed that the melilite-rich inclusions and spinel-pyroxene inclusions condensed in the solar nebula, and the hibonite-bearing inclusions crystallized from melts. The heavy alteration of the inclusions in Yamato 791717, which probably took place under a very oxidizing condition in the solar nebular, is also confirmed.

— Enstatite chondrites are classified into EH and EL groups, and some of them were melted once. In this paper, we report petrography and mineral chemistry of five new Antarctic enstatite chondrites. Yamato 793225 is characterized by intermediate properties between the EH and EL groups and probably represents a new grouplet of enstatite chondrites. The three paired meteorites (Y-8404, Y-8414 and Y-86004) may have cooled rapidly near the surface of the parent body as impact EH melt rocks. Yamato 82189 is also classified as EH melt rock, but it experienced slow cooling as did Y-793225. Yamato 82189 contains the first occurrence of phlogopite in enstatite meteorites.

Grove Mountains (GRV) 020090 is an enriched lherzolitic shergottite, distinct from other lherzolitic shergottites, except RBT 04262/1. Its characteristics include high abundance of plagioclase (24.2 vol% in the nonpoikilitic area), presence of K-feldspar, common occurrence of baddeleyite, high FeO contents of olivine (bimodal peaks at Fa 33 mol% and Fa 41 mol%) and low-Ca pyroxenes (bimodal peaks at Fs 23.8–31.7 mol% and Fs 25.7–33.9 mol%), and significant LREE enrichment of phosphates (500–610 × CI). The bulk composition of GRV 020090 suggests derivation from partial melting of an enriched reservoir. However, the REE patterns of the cores of pigeonite oikocrysts and the olivine chadacrysts are indistinguishable from those of GRV 99027 and other moderately depleted lherzolitic shergottites, and reveal a LREE-depleted pattern of the primordial parent magma. We propose that the primordial parent magma of GRV 020090 was derived from a moderately depleted Martian upper mantle reservoir, and later the residual melt was contaminated by oxidized and enriched Martian crustal materials as it ascended up to the subsurface. GRV 020090 and RBT 04262/1 may have sampled an igneous unit different from other lherzolitic shergottites.

Y984028 is a new lherzolitic shergottite, consisting of poikilitic and non-poikilitic lithologies. The mafic silicates are FeO-poor, and the chromite is TiO2-poor in the poikilitic lithology compared to the grains in the non-poikilitic lithology. This meteorite shares similar mineral petrography and mineral chemistry with GRV 99027, but is not paired with the latter because of their different shock-induced features. Y984028 was severely shocked and experienced no significant thermal metamorphism after the main impact event. Hence, Y984028 serves as a probe for the study of meteorite impact processes on terrestrial surfaces. The melt veins in Y984028 are characterized by the absence of any high-pressure polymorphs, the presence of abundant small mineral fragments, and the prevailing granulation textures of olivine and chromite. These features are consistent with adiabatic melting during the release of shock-induced high-pressure and quenching at ambient pressure.