Natural dissociation of olivine to (Mg,Fe)SiO3 perovskite and magnesiowüstite in a shocked Martian meteorite

Masaaki Miyahara, Eiji Ohtani, Shin Ozawa, Makoto Kimura, Ahmed El Goresy, Takeshi Sakai, Toshiro Nagase, Kenji Hiraga, Naohisa Hirao, Yasuo Ohishig

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34 Citations (Scopus)

Abstract

We report evidence for the natural dissociation of olivine in a shergottite at high-pressure and high-temperature conditions induced by a dynamic event on Mars. Olivine (Fa34-41) adjacent to or entrained in the shock melt vein and melt pockets of Martian meteorite olivine-phyric shergottite Dar al Gani 735 dissociated into (Mg,Fe)SiO3 perovskite (Pv)+magnesiowüstite (Mw), whereby perovskite partially vitrified during decompression. Transmission electron microscopy observations reveal that microtexture of olivine dissociation products evolves from lamellar to equigranular with increasing temperature at the same pressure condition. This is in accord with the observations of synthetic samples recovered from high-pressure and high-temperature experiments. Equigranular (Mg,Fe)SiO 3 Pv and Mw have 50-100 nm in diameter, and lamellar (Mg,Fe)SiO 3 Pv and Mw have approximately 20 and approximately 10 nm in thickness, respectively. Partitioning coefficient, KPv-Mw=[FeO-MgO]/ FeO-MgO]Mw, between (Mg,Fe)SiO3 Pv and Mw in equigranular and lamellar textures are approximately 0.15 and approximately 0.78, respectively. The dissociation of olivine implies that the pressure and temperature conditions recorded in the shock melt vein and melt pockets during the dynamic event were approximately 25 GPa but 700 °C at least.

Original languageEnglish
Pages (from-to)5999-6003
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume108
Issue number15
DOIs
Publication statusPublished - 2011 Apr 12

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