High‐pressure polymorphs in Yamato‐790729 L6 chondrite and their significance for collisional conditions

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  • Yukako Kato
    Department of Earth and Planetary Systems Science Graduate School of Science Hiroshima University Higashi‐Hiroshima 739‐8526 Japan
  • Toshimori Sekine
    Department of Earth and Planetary Systems Science Graduate School of Science Hiroshima University Higashi‐Hiroshima 739‐8526 Japan
  • Masahiko Kayama
    Department of Earth and Planetary Systems Science Graduate School of Science Hiroshima University Higashi‐Hiroshima 739‐8526 Japan
  • Masaaki Miyahara
    Department of Earth and Planetary Systems Science Graduate School of Science Hiroshima University Higashi‐Hiroshima 739‐8526 Japan
  • Akira Yamaguchi
    National Institute of Polar Research Tokyo 190‐8518 Japan

書誌事項

公開日
2017-09-25
権利情報
  • http://onlinelibrary.wiley.com/termsAndConditions#vor
DOI
  • 10.1111/maps.12957
公開者
Wiley

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<jats:title>Abstract</jats:title><jats:p>Shock pressure recorded in Yamato (Y)‐790729, classified as L6 type ordinary chondrite, was evaluated based on high‐pressure polymorph assemblages and cathodoluminescence (<jats:styled-content style="fixed-case">CL</jats:styled-content>) spectra of maskelynite. The host‐rock of Y‐790729 consists mainly of olivine, low‐Ca pyroxene, plagioclase, metallic Fe‐Ni, and iron‐sulfide with minor amounts of phosphate and chromite. A shock‐melt vein was observed in the hostrock. Ringwoodite, majorite, akimotoite, lingunite, tuite, and xieite occurred in and around the shock‐melt vein. The shock pressure in the shock‐melt vein is about 14–23 GPa based on the phase equilibrium diagrams of high‐pressure polymorphs. Some plagioclase portions in the host‐rock occurred as maskelynite. Sixteen different <jats:styled-content style="fixed-case">CL</jats:styled-content> spectra of maskelynite portions were deconvolved using three assigned emission components (centered at 2.95, 3.26, and 3.88 eV). The intensity of emission component at 2.95 eV was selected as a calibrated barometer to estimate shock pressure, and the results indicate pressures of about 11–19 GPa. The difference in pressure between the shock‐melt vein and host‐rock might suggest heterogeneous shock conditions. Assuming an average shock pressure of 18 GPa, the impact velocity of the parent‐body of Y‐790729 is calculated to be ~1.90 km s<jats:sup>−1</jats:sup>. The parent‐body would be at least ~10 km in size based on the incoherent formation mechanism of ringwoodite in Y‐790729.</jats:p>

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