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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: 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]

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]

We report a preliminary in situ finding of 60Ni isotopic anomalies, attributed to the decay of short-lived 60Fe (half-life 1.5 Ma), in Fe-sulfides and pyroxene in the Chervony Kut eucrite and in the Semarkona (LL3.0) ordinary chondrite using the new state-of-the-art NanoSIMS technique at MPI in Mainz. In Semarkona, troilites (FeS) show 60Ni excesses of up to 46 ± 15‰ (2σ). A positive correlation between 60Ni excesses and 56Fe/58Ni ratios provides evidence for live 60Fe in the early solar system. The inferred 60Fe/56Fe ratio of (7.3 ± 2.6) × 10−7 is much higher than previously estimated for the initial solar system value. In terms of a chronological interpretation, this corresponds to one half-life of 60Fe. In Chervony Kut, two pyrrhotite {Fe(1−x)S} types (abundant Pyr-1 crystals and rare Pyr-2 veins) and pyroxene {(Mg,Fe)SiO3} grains show 60Ni excesses. The delta-60Ni varies from 22 ± 16‰ (2σ) in Pyr-1 to an extremely high value of 1775 ± 250‰ in Pyr-2 veins. No clear correlation is seen between the 60Ni excess and the Fe/Ni ratio, which does not allow a plausible explanation for the extreme excess encountered in Pyr-2. More meticulous analyses are underway in order to confirm this preliminary finding. [Copyright &y& Elsevier]

Investigations on a polished thin section (PTS) by reflected-light microscopy, laser micro-Raman spectroscopy, and cathodoluminescence of the Bencubbin meteorite revealed the presence of diamond grains ranging in size from 200 nm to 1 μm in Fe–Ni metal, silicates, and at metal–silicate interfaces. Most of the diamonds are associated with poorly graphitized carbon (PGC). Nitrogen isotopic measurements with the new generation NanoSIMS 50 ion microprobe indicate the presence of two isotopically distinct types of nitrogen carriers: One carrier type consists of diamonds, their associated PGCs, and diamond-free PGCs (called group-B). It is N-poor and has isotopically close to normal N. The other carrier type consists only of diamond-free PGCs (called group-A), is N-rich and heavily enriched in 15N (δ15Nmax∼1000‰). The petrographic and Raman characteristics of the diamonds are indicative of formation by shock. The difference in the N-isotopic compositions of diamonds and the associated group-B PGCs on the one hand, and the group-A diamond-free PGCs on the other, suggests that a 15N-rich component was probably incorporated into the Bencubbin parent body in an episode subsequent to the shock event that induced carbon–diamond phase transformation from the pristine PGCs with isotopically normal nitrogen. In the second episode, presumably in a milder shock event, significant amounts of N were delivered and redistributed among different phases. The isotopically heavy N signature is hence not pristine to the Bencubbin parent body, but was brought in by a second impactor. [Copyright &y& Elsevier]

Highlights: • We investigate UltraCarbonaceous Antarctic micrometeorites composition. • They reveal a new N-rich organic matter from the Solar System. • This exceptional organic matter is formed in the Oort cloud. • Cosmic ray irradiation form this carbon nitride organic material. • A nitrogen rich snow line must exists in our Solar System. [ABSTRACT FROM AUTHOR]