Back-transformation mechanisms of ringwoodite and majorite in an ordinary chondrite

Kanta Fukimoto, Masaaki Miyahara, Takeshi Sakai, Hiroaki Ohfuji, Naotaka Tomioka, Yu Kodama, Eiji Otani, Akira Yamaguchi

Research output: Contribution to journalArticlepeer-review

Abstract

We investigated the back-transformation mechanisms of ringwoodite and majorite occurring in a shock-melt vein (SMV) of the Yamato 75267 H6 ordinary chondrite during atmospheric entry heating. Ringwoodite and majorite in the shock melt near the fusion crust have back-transformed into olivine and enstatite, respectively. Ringwoodite (Fa~18) occurs in the SMV as a fine-grained polycrystalline assemblage. Approaching the fusion crust, fine-grained polycrystalline olivine becomes dominant instead of ringwoodite. The back-transformation from ringwoodite to olivine proceeds by incoherent nucleation and by an interface-controlled growth mechanism: nucleation occurs on the grain boundaries of ringwoodite, and subsequently olivine grains grow. Majorite (Fs16–17En82–83Wo1) occurs in the SMV as a fine-grained polycrystalline assemblage. Approaching the fusion crust, the majorite grains become vitrified. Approaching the fusion crust even more, clino/orthoenstatite grains occur in the vitrified majorite. The back-transformation from majorite to enstatite is initiated by the vitrification, and growth continues by the subsequent nucleation in the vitrified majorite.

Original languageEnglish
Pages (from-to)1749-1763
Number of pages15
JournalMeteoritics and Planetary Science
Volume55
Issue number8
DOIs
Publication statusPublished - 2020 Aug 1
Externally publishedYes

ASJC Scopus subject areas

  • Geophysics
  • Space and Planetary Science

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