¹Leanne G.Staddon,¹James R.Darling,²Winfried H.Schwarz,³Natasha R.Stephen,¹Sheila Schuindt,¹Joseph Dunlop,⁴Kimberly T.Tait
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.09.034]
¹School of the Environment, Geography and Geoscience, University of Portsmouth, Portsmouth, PO1 3QL, United Kingdom
²Institute of Earth Sciences, Heidelberg Ion Probe, Heidelberg University, 69120 Heidelberg, Germany
³Plymouth Electron Microscopy Centre, University of Plymouth, Plymouth, PL4 8AA, United Kingdom
⁴Department of Natural History, Royal Ontario Museum, Toronto, ON, M5S 2C6, Canada
Copyright Elsevier

Baddeleyite (monoclinic; m-ZrO2) is a widespread accessory phase within shergottites. However, the effects of shock loading on baddeleyite U-Pb isotopic systematics, and therefore its reliability as a geochronometer within highly shocked lithologies, are less well constrained. To investigate the effects of shock metamorphism on baddeleyite U-Pb chronology, we have conducted high-resolution microstructural analysis and in-situ U-Pb isotopic measurements for baddeleyite within enriched basaltic shergottites Northwest Africa (NWA) 7257, NWA 8679 and Zagami. Electron backscatter diffraction (EBSD) analyses of baddeleyite reveal significant microstructural heterogeneity within individual thin sections, recording widespread partial to complete reversion from high-pressure (≥ 3.3 GPa) orthorhombic zirconia polymorphs. We define a continuum of baddeleyite microstructures into four groupings on the basis of microstructural characteristics, including rare grains that retain magmatic twin relationships. Uncorrected U-Pb isotopic measurements form Tera-Wasserburg discordia, yielding new 238U-206Pb discordia ages of 195 ± 15 Ma (n = 17) for NWA 7257 and 220 ± 23 Ma (n = 10) for NWA 8679. Critically, there is no resolvable link between baddeleyite microstructure and U-Pb isotope systematics, indicating negligible open-system behaviour of U-Pb during zirconia phase transformations. Instead, we confirm that high post-shock temperatures exert the greatest control on Pb mobility within shocked baddeleyite; in the absence of high post-shock temperatures, baddeleyite yield robust U-Pb isotope systematics and date the age of magmatic crystallization. Low bulk post-shock temperatures recorded within Zagami (≤ 220 °C), and suggested within NWA 7257 and NWA 8679 by baddeleyite microstructure and other petrological constraints, confirm that the previously derived baddeleyite age of Zagami records magmatic crystallization, and provide greater age diversity to 225 Ma to 160 Ma enriched shergottites. While our data yield no resolvable link between microstructure and U-Pb isotopic composition, we strongly recommend that microstructural analyses should represent an essential step of baddeleyite U-Pb chronology within planetary (e.g., martian, lunar, asteroidal) and shocked terrestrial samples, allowing full contextualisation prior to destructive isotopic techniques. Microstructurally constrained in-situ U-Pb analyses of baddeleyite thus define new opportunities for the absolute chronology of martian meteorites and, more broadly, shocked planetary materials.

^1,2Paula Izquierdo,³Odette Toloza,^3,4Boris T Gänsicke,^1,2Pablo Rodríguez-Gil,⁵Jay Farihi,⁶Detlev Koester,⁵Jincheng Guo,⁷Seth Redfield
Monthly Notices of the Royal Astronomical Society  501, 4276–4288, Link to Article [https://doi.org/10.1093/mnras/staa3987]
¹Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain
²Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
³Department of Physics, University of Warwick, Coventry CV4 7AL, UK
⁴Center for Exoplanets and Habitability, University of Warwick, Coventry CV4 7AL, UK
⁵Department of Physics and Astronomy, University College London, London WC1E 6BT, UK
⁶Institut für Theoretische Physik und Astrophysik, Universität Kiel, D-24098 Kiel, Germany
⁷Department of Astronomy and Van Vleck Observatory, Wesleyan University, Middletown, CT 06459, USA

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^1,2Vladimir V Busarev,³Elena V Petrova,¹Marina P Shcherbina,¹Natalia P Ikonnikova,¹Marina A Burlak,¹Alexander A Belinski
Monthly Notices of the Royal Astronomical Society 502, 1882-1894 Link to Article [https://doi.org/10.1093/mnras/staa4022]
¹Lomonosov Moscow State University, Sternberg Astronomical Institute (SAI MSU), Universitetskii 13, Moscow 119992, Russia
²Institute of Astronomy, Russian Academy of Science, Pyatnitskaya 48, Moscow 109017, Russia
³Space Research Institute, Russian Academy of Sciences (IKI RAS), Profsoyuznaya 84/32, Moscow 117997, Russia

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¹David W. Mittlefehldt,²Richard C. Greenwood,³Eve L. Berger,⁴Loan Le,⁴Zhan X. Peng,^4,5D. Kent Ross
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13730]

¹Mail code XI3, Astromaterials Research Office, NASA/Johnson Space Center, Houston, Texas, 77058 USA
²Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA UK
³Texas State University—Jacobs JETS Contract, NASA Johnson Space Center, Houston, Texas, 77058 USA
⁴Jacobs JETS-NASA Johnson Space Center, Houston, Texas, 77058 USA
⁵UTEP-CASSMAR, El Paso, Texas, 79968 USA
Published by arrangement with John Wiley & Sons

We report petrologic studies and oxygen isotope analyses of normal and anomalous eucrites, termed eucrite-type achondrites. Petrologically anomalous eucrite-type achondrites can have normal oxygen isotope compositions, and vice versa. Two basaltic eucrites with normal oxygen isotope compositions contain pyroxenes with anomalous Fe/Mn engendered by parent body processes acting on normal eucrites: solid-state reduction by S gas in EET 87542, and reduction during crystallization by magmatic S in QUE 94484. Cataclastic basaltic breccias PCA 82502 and PCA 91007 are paired (petrology, anomalous oxygen). Although isotopically like Pasamonte, they are petrologically distinct. We confirm the petrological and isotopic anomalies of cumulate gabbro EET 92023; likely formed by impact melting of mixed cumulate and basaltic materials. Many main group eucrites include plagioclases that retain near-liquidus compositions despite metamorphic overprinting. Stannern group eucrites contain more sodic plagioclase, which is consistent with the melt hybridization hypothesis for Stannern group magma formation. The lack of more calcic plagioclase suggests reactive exchange of the anorthite component of the primary melt with the albitic component of the crust. Asteroids that are modestly different in composition can produce virtually indistinguishable basalts, providing a ready explanation for the eucrite-type achondrite suite. Small stochastic variations in petrologic evolution can cause substantial differences in rocks produced on an asteroid.

¹Y Ellinger,¹M Lattelais,¹F Pauzat,²J-C Guillemin,³B Zanda
Monthly Notices of the Royal Astronomical Society 502, 4064–4073 Link to Article [https://doi.org/10.1093/mnras/stab217]
¹Sorbonne Université, CNRS – UMR7616, LCT, 4 Place Jussieu, F-75005 Paris, France
²Univ Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, ISCR UMR6226, F-35000 Rennes, France
³Sorbonne Université, CNRS – UMR7202, MNHN, 61 rue Buffon, F-75005 Paris, France

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^1,2,3Jarmo Moilanen,^1,2,3,4Maria Gritsevich,³Esko Lyytinen
Monthly Notices of the Royal Astronomical Society 503, 3337–3350 Link to Article [https://doi.org/10.1093/mnras/stab586]
¹Finnish Geospatial Research Institute (FGI), Geodeetinrinne 2, FI-02430 Masala, Finland
²University of Helsinki, Faculty of Science, Gustaf Hällsrömin katu 2, FI-00014 Helsinki, Finland
³Finnish Fireball Network, Ursa Astronomical Association, Kopernikuksentie 1, FI-00130 Helsinki, Finland
⁴Institute of Physics and Technology, Ural Federal University, Ekaterinburg 620002, Russia

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¹Sujoy Ghosh¹Kishan Tiwari,²Masaaki Miyahara,³Arno Rohrbach,³Christian Vollmer,⁴Vincenzo Stagno,⁵Eiji Ohtani,⁶Dwijesh Ray
Proceedings of the National Academy of the United States of America (in press) Link to Article [https://doi.org/10.1073/pnas.2108736118]
¹Department of Geology and Geophysics, Indian Institute of Technology Kharagpur, Kharagpur 721302, India;
²Graduate School of Advanced Science and Engineering, Hiroshima University, Hiroshima 739-8526, Japan;
³Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany;
⁴Department of Earth Sciences, Sapienza University of Rome, Rome 00185, Italy;
⁵Department of Earth and Planetary Materials Science, Graduate School of Sciences, Tohoku University, Sendai 980-8578, Japan;
⁶Planetary Sciences Division, Physical Research Laboratory, Ahmedabad 380009, India

Bridgmanite, the most abundant mineral of the Earth’s lower mantle, has been reported in only a few shocked chondritic meteorites; however, the compositions of these instances differ from that expected in the terrestrial bridgmanite. Here, we report the first natural occurrence of Fe-bearing aluminous bridgmanite in shock-induced melt veins within the Katol L6 chondrite with a composition that closely matches those synthesized in high-pressure and temperature experiments over the last three decades. The Katol bridgmanite coexists with majorite and metal-sulfide intergrowths. We found that the natural Fe-bearing aluminous bridgmanite in the Katol L6 chondrite has a significantly higher Fe³⁺/ΣFe ratio (0.69 ± 0.08) than coexisting majorite (0.37 ± 0.10), which agrees with experimental studies. The Katol bridgmanite is arguably the closest natural analog for the bridgmanite composition expected to be present in the Earth’s lower mantle. Textural observations and comparison with laboratory experiments suggest that the Katol bridgmanite formed at pressures of ∼23 to 25 gigapascals directly from the chondritic melt generated by the shock event. Thus, the Katol L6 sample may also serve as a unique analog for crystallization of bridgmanite during the final stages of magma ocean crystallization during Earth’s formation.