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We report in situ NanoSIMS siderophile minor and trace element abundances in individual Fe-Ni metal grains in the unequilibrated chondrite Krymka (LL3.2). Associated kamacite and taenite of 10 metal grains in four chondrules and one matrix metal were analyzed for elemental concentrations of Fe, Ni, Co, Cu, Rh, Ir, and Pt. The results show large elemental variations among the metal grains. However, complementary and correlative variations exist between adjacent kamacite-taenite. This is consistent with the unequilibrated character of the chondrite and corroborates an attainment of chemical equilibrium between the metal phases. The calculated equilibrium temperature is 446 ± 9 °C. This is concordant with the range given by Kimura et al. (2008) for the Krymka postaccretion thermal metamorphism. Based on Ni diffusivity in taenite, a slow cooling rate is estimated of the Krymka parent body that does not exceed ~1K Myr-1, which is consistent with cooling rates inferred by other workers for unequilibrated ordinary chondrites. Elemental ionic radii might have played a role in controlling elemental partitioning between kamacite and taenite. The bulk compositions of the Krymka metal grains have nonsolar (mostly subsolar) element/Ni ratios suggesting the Fe-Ni grains could have formed from distinct precursors of nonsolar compositions or had their compositions modified subsequent to chondrule formation events. [ABSTRACT FROM AUTHOR]

Introduction: Regolith samples of the carbonaceous asteroid 162173 Ryugu were returned by the Hayabusa2 spacecraft in December 2020. Preliminary investigation of selected grains from each sampling site has revealed the occurrence of an abundant macromolecular insoluble material, similar to that of carbonaceous chondrites [1]. Understanding the origin of organic matter on carbonaceous asteroids and its subsequent evolution due to secondary processes as well as space weathering is one of the prime goals of the Hayabusa2 sample-return mission. Isotope composition of organic material found in extraterrestrial samples is a powerful proxy for tracking its origin and evolution during the solar system events [2]. To document the H- and N-isotope signatures of IOM contained in the Ryugu samples, we have used the NanoSIMS installed at the National Muséum of Natural History in Paris. We present here data acquired on the IOM isolated from grains of two touchdown sites. We have imaged between 2800 and 3200 ?m2 of the IOM of chamber A and C, respectively. The comparison with the IOM of carbonaceous chondrites allows for evaluating the influence of space weathering and aqueous alteration on the IOM in carbonaceous asteroids. Results: N-isotope distributions: the bulk δ15N is +17.4‰ and +30‰ for the IOM of chamber A and chamber C, respectively. These IOMs contain both 15N-enriched and depleted carbonaceous grains, with 180‰<δ15N< 800‰ for hotspots and -380‰ < δ15N < -180‰ for coldspots. Hotspots define a Poisson distribution with a mode value of +241‰ and +348‰ for chamber A and chamber C, respectively. Elemental ratios: Bulk N/C, O/C and S/C of Ryugu IOM are 0.035, 0.12, 0.032, respectively, for chamber A and 0.027, 0.04, 0.025 for chamber C. The N/C ratio of individual 15N-rich and depleted grains are comprised between 0.01 and 0.07, with those in the IOM of A0106 being slightly more N rich. Similarly, O/C and S/C ratios are also slightly higher in A0106. H-isotope distribution: Ryugu IOM exhibits bulk enrichments in D with δD = +306‰ and +440‰ for chamber A and chamber C, respectively. Numerous D-rich hotspots, are observed, with +600‰ < δD < +6000‰. They define a Poisson distribution, with a mode value of +1030‰ and +1374‰ for chamber A and chamber C, respectively. Of note, a few D-depleted organic grains are also observed (-200‰ < δD < 0‰). Discussion: Subtle differences are observed between the IOM of chamber A and chamber C: the IOM is less enriched in heavy isotopes in chamber A, and more enriched in N, O and S. This may reflect some heterogeneity at the scale of the asteroid, or the influence of sampling depth, hence the influence of space weathering. However, the elemental and isotope compositions of the IOM in Ryugu are comparable to those of hydrated carbonaceous chondrites. The bulk δ15N in Ryugu IOM is commensurable to levels reported in CI chondrites, despite the occurrence of hotspots being more 15N-rich in Ryugu [3]. The range of δ15N covered by these hotspots is, however, consistent with the IOM of CM chondrites and Tagish Lake, but remains in the lower end of the hotspots in CR chondrites. The most notable difference is the bulk δD which is lower than in the IOM of hydrated carbonaceous chondrites. The distribution of δD in Ryugu IOM is consistent with the IOMs in CI and CM chondrites. We did not observe enrichments as large as those reported in CR chondrites and in Tagish Lake [4,5]. The abundance of D- and 15N-rich hotspots appears similar in Ryugu and carbonaceous chondrites. Differences between Ryugu and carbonaceous chondrites may result from different intensity of aqueous alteration or the impact of space weathering, which could have induced a decrease of D/H in organic compounds by H implantation. Acknowledgments: The NanoSIMS facility at MNHN in Paris is supported by CNRS and MNHN. L. R. is grateful to the European Research Council (ERC consolidator grant HYDROMA). [ABSTRACT FROM AUTHOR]

Introduction: High pressure minerals from meteoritic shock melt veins are key to understand the collisional history of the Solar System. The L chondrites, the most shocked meteorites [1], present abundant shock melt veins from which we can retrace their history. To this day, their family of origin is still debated. The shock timescale of 7 chondrites was measured to deduce their parent body diameters. Moreover, we use tuite, a high pressure phosphate mineral to perform U-Pb datation by SIMS. We find a bimodal distribution of ages, which match closely the ages previously obtained for Creston and Novato, two other shocked L6 chondrites [2]. Samples and Methods: Seven samples were first studied by optical microscopy and Raman spectroscopy to identify high pressure (HP) polymorphs. Scanning Transmission Electron Microscopy (STEM) was then used to study microstructures and transformation/growth mechanisms. The EDX was used to locate eligible minerals for datation (phosphates). Combined STEM-EDX (UMET, Lille, France) and NanoSIMS (MNHN, Paris, France) chemical maps were finally collected on the same FIB sections in order to compare these two analytical approaches and produce chemical maps. The U and Pb isotope concentrations where then measured on the identified tuite grains with the help of a Cameca IMS 1280 LG SIMS (CRPG, Nancy France) for datation. Results: Multiple high pressure textures were observed in all seven samples. Polycristalline assemblages of ringwoodite are typically the dominant texture, but more exotic textures were also found. Some meteorites present ringwoodite as lamellae inside olivine crystals, whereas others seem to present an assemblage of MgSiO3 glass with akimotoite crystallites. Both these textures allowed us to investigate elemental diffusion induced by structural changes. We therefore calculated shock timescales following the methods described in [3,4]. For all our samples, assuming a temperature of 2400K [5], shock timescales ranging between 0.5 and 20 seconds were derived. The meteorites that do not contain ringwoodite lamellae have significantly higher shock timescales, between 11 and 16 seconds. These larger shock timescales were caused by an impact between larger bolides, including a parent body of at least 150km wide. This is significantly higher than parent-bodies with diameters around 70km required by the other group. In almost all meteorites, we find tuites inside the shock melt veins. The meteorites that do not contain tuite have at least shocked apatites and whitlockites, with shifted Raman spectra indicating a change in structure. We date both the host rock apatites and the shock vein phosphates. This allows us to obtain conclusive collision ages from a normal concordia diagram for two of our samples, one of each group. The tuites record collisions ages of 461+-57Ma for the group with the largest parent body, and 650+-160Ma for the group with the smaller parent body. The host rock minerals record upper intercepts of 4481Ma in both meteorites. Conclusion: Shocked L chondrites seem to define two groups, which are texturally different and appear to have a completely different history. A smaller, 70km-wide parent body exploded first (650 Ma ago) and yielded most of the shocked meteorites, and a larger one exploded in the cataclysmic collision known today as the "L chondrite parent body breakup" 470Ma ago. The upper intercept of 4481Ma could date the early separation of the original L chondrite parent body into different families. [ABSTRACT FROM AUTHOR]

- We report the 53Mn-53Cr systematics of three dolomite grains from two different CI1 clasts contained within the Kaidun meteorite breccia. Three internal isochrones result in initial 53Mn/55Mn ratios of (4.2 ± 0.4) × 10−6, (4.6 ± 1.3) × 10−6, and (5.2 ± 1.1) × 10−6. These initial values are consistent with those measured for dolomite in the Orgueil CI1 chondrite (; ) but significantly lower than the initial ratio determined by from a combination of different carbonate types within various lithologies of the Kaidun meteorite. We construct an accretion scenario for the Kaidun breccia by comparing the mineralogy and formation time scales of carbonates in the Kaidun CI1 lithologies to the analogous ones of the CI1 chondrite Orgueil. In Orgueil, dolomite precipitation precedes the formation of the first bruennerite grains by a few million years (; ). As the CI1 clasts in Kaidun lack breunnerite grains, and considering that aqueous alteration occurred prior to reaccretion of the various clasts onto the Kaidun parent body (e.g., ), we hypothesize that after rapid accretion and early aqueous alteration occurring within the first approximately 4 Myr after solar system formation, impact disruption of several asteroids and their reassembly into the Kaidun parent asteroid was complete within an additional approximately 2 Myr. This confirms that aqueous alteration, impact, and reaccretion of material in the asteroid belt were early processes that began contemporaneously with chondrule formation. [ABSTRACT FROM AUTHOR]

The accretion of the terrestrial planets from asteroid collisions and the delivery to the Earth of martian and lunar meteorites has been modelled extensively. Meteorites that have experienced shock waves from such collisions can potentially be used to reveal the accretion process at different stages of evolution within the Solar System. Here we have determined the peak pressure experienced and the duration of impact in a chondrite and a martian meteorite, and have combined the data with impact scaling laws to infer the sizes of the impactors and the associated craters on the meteorite parent bodies. The duration of shock events is inferred from trace element distributions between coexisting high-pressure minerals in the shear melt veins of the meteorites. The shock duration and the associated sizes of the impactor are found to be much greater in the chondrite (∼1 s and 5 km, respectively) than in the martian meteorite (∼10 ms and 100 m). The latter result compares well with numerical modelling studies of cratering on Mars, and we suggest that martian meteorites with similar, recent ejection ages (105 to 107 years ago) may have originated from the same few square kilometres on Mars. [ABSTRACT FROM AUTHOR]