¹Christopher D. K. Herd
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13935]
¹Department of Earth and Atmospheric Sciences, University of Alberta, 1–26 Earth Sciences Building, Edmonton, Alberta, T6G 2E3 Canada
Published by arrangement with John Wiley & Sons

The petrogenesis of the Northwest Africa (NWA) 7635 Martian meteorite involved the entrainment of xenocrystic olivine grains into a relatively magnesian and oxidized melt, followed by a redox-dependent reaction between olivine and melt that resulted in the crystallization of orthopyroxene and magnetite. Subsequent crystallization of the melt began with augite, plagioclase, and magnetite phenocrysts, and was followed by crystallization of augite, plagioclase, magnetite, ilmenite, and pyrrhotite in the groundmass, which took place under more rapid conditions of cooling, as reflected in the groundmass grain size. The petrogenetic history of NWA 7635 is similar in many ways to that of NWA 8159; this observation, coupled with similarities in geochemical and isotopic characteristics from other studies, suggests that the parent melts of the two rocks—as represented by all minerals except the xenocrystic olivine—were one and the same. The main distinctions between the two rocks are that their parent melts entrained xenocrystic olivine of different composition, and the cooling rate of the groundmass of NWA 7635 was more rapid than that of NWA 8159. The conclusion that the redox reaction took place between olivine and melt is in contrast to other work that suggests the reaction took place in the subsolidus, and has implications for the nature of the reaction in both NWA 7635 and NWA 8159.

^1,3Ming-Chang Liu,²Marc Chaussidon,¹Nozomi Matsuda
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.12.001]
¹Department of Earth, Planetary, and Space Sciences, UCLA, Los Angeles, CA, USA
²Université de Paris Cité , Institut de Physique du Globe de Paris, CNRS, 1 rue Jussieu, Paris 75005 France
³Lawrence Livermore National Laboratory, Livermore, CA, USA
Copyright Elsevier

The origin of solar 11B/10B ratio ∼4 remains an open question. It has been thought that a significant portion of boron in the Solar System was derived from continuous spallation nucleosynthesis during interactions between Galactic Cosmic Rays and C-N-O nuclei in the interstellar medium. However, because GCR-produced boron is characterized by 11B/10B ∼2.5, an endmember with 11B/10B > 4 is required to account for the solar 11B/10B ratio. Two leading hypotheses for the sources of 11B-rich components include low energy spallation in the Sun’s parental molecular cloud and the neutrino process during the supernova explosions. In this study, lithium and boron elemental and isotopic compositions of seven porphyritic olivine chondrules and one isolated olivine crystal from four meteorites (Allende, Yamato 81020, Asuka 12236, and QUE 97008) were determined in-situ to help constrain which of the two nucleosynthetic mechanisms has most likely supplied the forming Solar System with extra 11B. Apparent isotopic variations in Li/Si, B/Si, δ7Li and δ11B were found in chondrule olivine crystals, but only three chondrules exhibit statistically resolved δ11B heterogeneities. Using these three chondrules as a basis for discussion, we evaluated the processes that could potentially cause elemental and isotopic variations of Li and B. We argue that the data can be best understood in the context of condensation of lithium-boron-rich material onto chondrule precursors in (an) initially heterogeneous gaseous reservoir(s), which could be realized if the Solar System derived 11B-rich components from a supernova or supernovae.

^1,2,3,4Sky P. Beard,^2,3Timothy D. Swindle,⁵Thomas J. Lapen,^2,3David A. Kring
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13927]
¹State Key Laboratory in Lunar and Planetary Science, Macau University of Science and Technology, Avenida Wai Long, Macau, Taipa, 999078 P.R. China
²NASA Solar System Exploration Research Virtual Institute, Moffett Field, California, 94035 USA
³Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, 85721 USA
⁴CNSA Macau Center for Space Exploration and Science, Macau, P.R. China
⁵University of Houston, Houston, Texas, 77004 USA
Published by arrangement with John Wiley & Sons

The LL5 chondrite Chelyabinsk has had numerous isotopic studies since its fall in 2013. These data have been used to suggest ~8 impact events recorded from multiple isotopic systems (e.g., Ar-Ar, U–Pb, Sm-Nd, Rb-Sr, among others). We report details of Ar-Ar and U-Pb results and re-evaluate the geochronology of Chelyabinsk. Argon has the youngest Ar-Ar age recorded in meteorites, 25 ± 11 Ma, and an older resetting event at ~2550 Ma. The U-Pb analysis has an upper concordia age of 4456 ± 23 Ma and a lower concordia age of 184 ± 200 Ma. The lower concordia intercept represents a later thermal event (e.g., an impact), the most recent time that lead loss occurred, and could represent resetting by the youngest event recorded by Ar-Ar. Combining our data with literature results, we find strong evidence of at least four impact events (~4450, 2550, 1700, 25 Ma), with some evidence for two additional impacts (~3700, 1000 Ma).

¹Lukáš Shrbený,²Agata M. Krzesińska,¹Jiří Borovička,¹Pavel Spurný,³Zbigniew Tymiński,⁴Kryspin Kmieciak
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13929]
¹Astronomical Institute of the Czech Academy of Sciences, Ondřejov, 251 65 Czech Republic
²Centre for Earth Evolution and Dynamics, Department of Geosciences, University of Oslo, Oslo, N-0371 Norway
³National Centre for Nuclear Research, POLATOM Radioisotope Centre, Otwock, 05-400 Poland
⁴Meteorite Finder
Published by arrangement with John Wiley & Sons

We present the description of an observation of a fireball recorded during the sunrise on July 15, 2021. Atmospheric trajectory, impact area, and heliocentric orbit were determined on the basis of three instrumental video records. The terminal part of the fireball was not instrumentally recorded due to clouds. Based on our computations, one meteorite was found in the predicted impact area by Polish searchers. The specimen was, soon after recovery, analyzed for the presence of short-lived radionuclides and the measurement confirms a very fresh fall, coinciding with the time of the fireball event. The recovered meteorite, Antonin, is an unbrecciated L5 chondrite with shock stage S3, weathering grade W0, and bulk density of 3.42 g cm−3. Unusual for L chondrites, it contains assemblages composed of metal and two sulfides, troilite and mackinawite. We interpret these assemblages to have been formed as products of shock metamorphism and post-shock annealing on the parent body. This suggests that the thermal and collisional history of the Antonin parent body was complex.

¹Cyril Sturtz,¹Angela Limare,¹Stephen Tait,¹Édouard Kaminski
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2021JE007020]
¹Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, Paris, F-75005 France
Published by arrangement with John Wiley & Sons

This is the second of two companion papers that present a theoretical and experimental study of the thermal history of planetesimals in which heating by short-lived radioactive isotopes generates an internal magma ocean and the subsequent cooling and crystallization thereof. We study the conditions required to form and preserve basal cumulates and flotation crusts, and the implications for the thermal evolution of planetary bodies. Our model predicts that planetesimals larger than 30km can reach 1300oC and a melt fraction of 40 vol%, producing a solid-like to liquid-like rheological transition that triggers an internal magma ocean. In the magma ocean regime core-mantle differentiation occurs very quickly and the mantle convects under a relic of chondritic material whose thickness is controlled by the temperature of rheological transition. We show that the magma ocean episode is associated with time-dependent crystal segregation and no re-entrainment. Segregation of crystals is essentially constrained by their size and by their density difference with respect to the melt, the latter being fully determined by the planetesimal’s initial composition. Olivine cumulates are likely to form at the core-mantle boundary. Under certain particular conditions, a flotation crust can also form, which reduces the efficiency of heat evacuation by convection, thereby enhancing the magma ocean’s lifetime and the efficiency of crystal segregation. Two types of large-scale mantle structure are possible outcomes: a well-mixed upper mantle above an olivine cumulate, or a more finely layered ”onion-shell” structure.

¹Suyu Fu,²Stella Chariton,²Vitali B. Prakapenka,³Andrew Chizmeshya,¹Sang-Heon Shim
American Mineralogist 107, 2307-2314 Link to Article [http://www.minsocam.org/msa/ammin/toc/2022/Abstracts/AM107P2307.pdf]
¹School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287, U.S.A.
²Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, U.S.
Copyright: The Mineralogical Society of America

Light elements alloying with metallic Fe can change the properties and therefore play a key role
in the structure and dynamics of planetary cores. Hydrogen and silicon are possible light elements in
the rocky planets’ cores. However, hydrogen storage in Fe-Si alloy systems remains unclear at high
pressures and high temperatures because of experimental difficulties. Taking advantage of pulsed laser
heating combined with high-energy synchrotron X‑ray diffraction, we studied reactions between FeSi
and H in laser-heated diamond-anvil cells (LHDACs) up to 61.9 GPa and 3500 K. We found that under
H-saturated conditions the amount of H alloying with FeSi (0.3 and <0.1 wt% for the B20 and B2 structures, respectively) is much smaller than that in pure Fe metal (>1.8 wt%). Our experiments also
suggest that H remains in the crystal structure of FeSi alloy when recovered to 1 bar. Further density
functional theory (DFT) calculations indicate that the low-H solubility likely results from the highly
distorted interstitial sites in the B20 and B2 structures, which are not favorable for H incorporation.
The recovery of H in the B20 FeSi crystal structure at ambient conditions could open up possibilities
to understand geochemical behaviors of H during core formation in future experiments. The low-H
content in FeSi alloys suggests that if a planetary core is Si-rich, Si can limit the ingassing of H into
the Fe-rich core.