Petrological, petrofabric, and oxygen isotopic study of five ungrouped meteorites related to brachinites

1Hikari Hasegawa,1,2Takashi Mikouchi,3,4Akira Yamaguchi,5Masahiro Yasutake,6Richard C. Greenwood,6Ian A. Franchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13249]
1Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, , Tokyo, 113‐0033 Japan
2The University Museum, The University of Tokyo, , Tokyo, 113‐0033 Japan
3Antarctic Meteorite Research Center, National Institute of Polar Research, Tachikawa, Tokyo, 190‐8518 Japan
4Department of Polar Science, School of Multidisciplinary Science, Graduate University for Advanced Sciences, Tachikawa, Tokyo, 190‐8518 Japan
5Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kyoto, 606‐8502 Japan
6 and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA UK
Published by arrangement with John Wiley & Sons

Northwest Africa (NWA) 6112, Miller Range (MIL) 090206 (plus its pairs: MIL 090340 and MIL 090405), and Divnoe are olivine‐rich ungrouped achondrites. We investigated and compared their petrography, mineralogy, and olivine fabrics. We additionally measured the oxygen isotopic compositions of NWA 6112. They show similar petrography, mineralogy, and oxygen isotopic compositions and we concluded that these five meteorites are brachinite clan meteorites. We found that NWA 6112 and Divnoe had a c axis concentration pattern of olivine fabrics using electron backscattered diffraction (EBSD). NWA 6112 and Divnoe are suggested to have been exposed to magmatic melt flows during their crystallization on their parent body. On the other hand, the three MIL meteorites have b axis concentration patterns of olivine fabrics. This indicates that the three MIL meteorites may be cumulates where compaction of olivine grains was dominant. Alternatively, they formed as residues and were exposed to olivine compaction. The presence of two different olivine fabric patterns implies that the parent body(s) of brachinite clan meteorites experienced diverse igneous processes.

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