¹Hideyuki Hayashi,²Takashi Mikouchi,³Nak Kyu Kim,³Changkun Park,^4,5Yuji Sano,^6,7Atsushi Takenouchi,⁶Akira Yamaguchi,⁸Hiroyuki Kagi,⁹Martin Bizzarro
Meteoritics & Planetary Science (in Press) Link to Article [https://onlinelibrary.wiley.com/doi/10.1111/maps.13776]
¹Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
²The University Museum, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
³Division of Earth Sciences, Korea Polar Research Institute (KOPRI), 26 Songdomirae-ro, Yeonsu-gu, Incheon, 21990 Korea
⁴Atmosphere and Ocean Research Institute (AORI), The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba, 277-8564 Japan
⁵Center for Advanced Marine Core Research, Kochi University, Monobe, Nankoku, Kochi, B200 783-8502 Japan
⁶Antarctic Meteorite Research Center, National Institute of Polar Research (NIPR), 10-3 Midori-cho, Tachikawa, Tokyo, 190-8518 Japan
⁷The Kyoto University Museum, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto, 606-8501 Japan
⁸Geochemical Research Center, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
⁹Centre for Stars and Planet Formation, Globe Institute, University of Copenhagen, ØsterVoldgade 5-7, Copenhagen, DK-1350 Denmark
Published by arrangement with John Wiley & Sons

Northwest Africa (NWA) 7203 is a quenched angrite, showing mineralogical features typically not present in other quenched angrites. NWA 7203 exhibits textures whose grain size varies from fine grains (<10 μm) to coarse grains (~3 mm), while other quenched angrites show only single-sized textures. Fine-grained and coarse-grained lithologies have nearly the same bulk compositions. Cooling rates were estimated to be ~80 °C h⁻¹ for fine-grained lithologies and ~1 °C h⁻¹ for coarse-grained lithologies. Mg-rich olivines (~Fo₆₄) were found only in fine-grained lithologies. Crystallization of NWA 7203 started in the fine-grained lithologies with Mg-rich olivine grains acting as seeds for crystallization. Coarse-grained lithologies were subsequently formed under conditions of slower cooling. NWA 7203 shows clear shock metamorphic textures unlike other quenched angrites except for NWA 1670. We confirm that the oxygen isotopic ratios of NWA 7203 plot on the angrite fractionation line within uncertainty. However, the obtained Pb-Pb age of NWA 7203 is 4543 ± 19 Ma, younger than the ages of other quenched angrites, which might be a result of disturbance by shock metamorphism. The finding of shock metamorphism of NWA 7203 suggests that some angrites might be derived from asteroids that remained large (>10 km in diameter) during the late heavy bombardment.