Fine‐structures of planar deformation features in shocked olivine: A comparison between Martian meteorites and experimentally shocked basalts as an indicator for shock pressure

1,2Atsushi Takenouchi,3Takashi Mikouchi,4Takamichi Kobayashi,5,6Toshimori Sekine,1,7Akira Yamaguchi,8Haruka Ono
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13367]
1National Institute of Polar Research (NIPR), 10‐3 Midori‐cho, Tachikawa, Tokyo, 190‐8518 Japan
2Department of Basic Science, The University of Tokyo, 3‐8‐1 Komaba, Meguro‐ku, Tokyo, 153‐8902 Japan
3The University Museum, The University of Tokyo, 7‐3‐1 Hongo, Bunkyo‐ku, Tokyo, 113‐0033 Japan
4National Institute for Materials Science (NIMS), 1‐1 Namiki, Tsukuba, Ibaraki, 305‐0044 Japan
5Center for High Pressure Science and Technology Advanced Research (HPSTAR), 1690 Cailun Rd, Pudong, Shanghai, 201203 P.R. China
6Graduate School of Engineering, Osaka University, 2‐1 Yamadaoka, Suita, Osaka, 565‐0871 Japan
7Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tachikawa, Tokyo, 190‐8518 Japan
8Department of Earth and Planetary Science, The University of Tokyo, 7‐3‐1 Hongo, Bunkyo‐ku, Tokyo, 113‐0033 Japan
Published by arrangement with John Wiley & Sons

We performed shock recovery experiments on an olivine‐phyric basalt at shock pressures of 22.2–48.5 GPa to compare with shock features in Martian meteorites (RBT 04261 and NWA 1950). Highly shocked olivine in the recovered basalt at 39.5 and 48.5 GPa shows shock‐induced planar deformation features (PDFs) composed of abundant streaks of defects. Similar PDFs were observed in olivine in RBT 04261 and NWA 1950 while those in NWA 1950 were composed of amorphous lamellae. Based on the present results and previous studies, the width and the abundance of lamellar fine‐structures increased with raising shock pressure. Therefore, these features could be used as shock pressure indicators while the estimated pressures may be lower limits due to no information of temperature dependence. For Martian meteorites that experienced heavy shocks, the minimum peak shock pressures of RBT 04261 and NWA 1950 are estimated to be 39.5–48.5 GPa and 48.5–56 GPa, respectively, which are found consistent with those estimated by postshock temperatures expected by the presence of brown olivine. We also investigated shock‐recovered basalts preheated at 750 and 800 °C in order to check the temperature effects on shock features. The results indicate a reduction in vitrifying pressure of plagioclase and a pressure increase for PDFs formation in olivine. Further temperature‐controlled shock recovery experiments will provide us better constraints to understand and to characterize various features found in natural shock events.

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