^1,2Guy Libourel,¹Clément Ganino,¹Marco Delbo,³Mathieu Niezgoda,⁴Benjamin Remy,⁵Lionel Aranda,¹Patrick Michel
Monthly Notices of the Royal Astronomical Society 500, 1905–1920 Link to Article [https://doi.org/10.1093/mnras/staa3183]
¹Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Université Côte d’Azur, UMR 7293, Boulevard de l’Observatoire, CS 34229, F-06304 Nice Cedex 4, France
²School of Ocean, Earth Science and Technology, Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI 96821, USA
³Commissariat à l’Energie Atomique et aux Energies Alternatives, CEA/DES/ISAS/DM2S/STMF/LMEC, PC 47, F-91191 Gif-sur-Yvette cedex, France
⁴Université de Lorraine, Laboratoire d’Energétique et de Mécanique Théorique Appliquée, CNRS, UMR 7563, 2 avenue de la Forêt de Haye, TSA 60604, F-54518 Vandoeuvre-les-Nancy Cedex, France
⁵Département Chimie et Physique des Solides et des Surfaces, Institut Jean Lamour, Université de Lorraine, UMR 7198, F-54000 Nancy, France

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^1,2Yohei Igami,¹Shunsuke Muto,³Aki Takigawa,¹Masahiro Ohtsuka,²Akira Miyake,⁴Kohtaku Suzuki,⁵Keisuke Yasuda,^6,7,8Akira Tsuchiyama
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.09.031]
¹Institute of Materials and Systems for Sustainability, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
²Division of Earth and Planetary Sciences, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan
³Department of Earth and Planetary Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
⁴The Wakasa Wan Energy Research Center, Tsuruga, Fukui 914-0192, Japan
⁵Graduate School of Life and Environmental Science, Kyoto Prefectural University, Shimogamo-Hangicho, Sakyo-ku, Kyoto 606-8522, Japan
⁶Research Organization of Science and Technology, Ritsumeikan University, Kusatsu 525-8577, Japan
⁷CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China
⁸CAS Center for Excellence in Deep Earth Science, Guangzhou 510640, China
Copyright Elsevier

Minerals on airless bodies exhibit characteristic spectral features such as darkening and reddening. Such space weathering is mainly due to hydrogen-ion irradiation by the solar wind and to micrometeorite impacts. Because of the reactivity of hydrogen, the associated H-implantation into O-bearing minerals can lead to the formation of new chemical bonds and may contribute to formation of water. However, laboratory studies still conflict about production efficiency of water and relevant H-bearing molecules such as OH formed by the H-ion irradiation. The production efficiency of the molecules within minerals may be influenced by short-range structural order of the host minerals. It is thus important to clarify how the implanted H interacts with various irradiation defects produced by H-ion bombardment. Here, we investigated H-ion-irradiated alumina (Al₂O₃), one of the most basic oxides, using scanning/transmission electron microscopy (S/TEM) and electron energy-loss spectroscopy (EELS). The TEM images revealed dense dislocations, nanoscale voids and nanoscale cracks—instead of amorphization—in the region subject to high energy deposition. Our analyses by STEM–EELS hyperspectral imaging (HSI) isolated a few essential spectral components, suggesting that chemical interactions between the implanted H and the host alumina resulted in local generation of OH species rather than amorphization. We also found a spectral feature which may be explained by H₂ gas, presumably remaining in the nanovoids, most of which escaped through fractures formed by the coalescence of the high-pressure H₂ nanobubbles. Such fractures/crack surfaces can act as additional reactive sites for the formation of the OH species. The present results strongly imply that H⁺ irradiation can be a source of water in minerals in various astrophysical conditions. The present methodology can be applied to a wide range of extraterrestrial materials, such as regolith grains, interplanetary-dust particles, and/or presolar grains in primitive meteorites.

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.