High-pressure phase transitions in FeCr2O4and structure analysis of new post-spinel FeCr2O4and Fe2Cr2O5phases with meteoritical and petrological implications

Takayuki Ishii, Hiroshi Kojitani, Shoichi Tsukamoto, Kiyoshi Fujino, Daisuke Mori, Yoshiyuki Inaguma, Noriyoshi Tsujino, Takashi Yoshino, Daisuke Yamazaki, Yuji Higo, Kenichi Funakoshi, Masaki Akaogi

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Abstract

We determined phase relations in FeCr2O4at 12-28 GPa and 800-1600 °C using a multi-anvil apparatus. At 12-16 GPa, FeCr2O4spinel (chromite) first dissociates into two phases: a new Fe2Cr2O5phase + Cr2O3with the corundum structure. At 17-18 GPa, the two phases combine into CaFe2O4-type and CaTi2O4-type FeCr2O4below and above 1300 °C, respectively. Structure refinements using synchrotron X-ray powder diffraction data confirmed the CaTi2O4-structured FeCr2O4(Cmcm), and indicated that the Fe2Cr2O5phase is isostructural to a modified ludwigite-type Mg2Al2O5(Pbam). In situ high-pressure high-temperature X-ray diffraction experiments showed that CaFe2O4-type FeCr2O4is unquenchable and is converted into another FeCr2O4phase on decompression. Structural analysis based on synchrotron X-ray powder diffraction data with transmission electron microscopic observation clarified that the recovered FeCr2O4phase has a new structure related to CaFe2O4-type. The high-pressure phase relations in FeCr2O4reveal that natural FeCr2O4-rich phases of CaFe2O4-and CaTi2O4-type structures found in the shocked Suizhou meteorite were formed above about 18 GPa at temperature below and above 1300 °C, respectively. The phase relations also suggest that the natural chromitites in the Luobusa ophiolite previously interpreted as formed in the deep-mantle were formed at pressure below 12-16 GPa.

Original languageEnglish
Pages (from-to)1788-1797
Number of pages10
JournalAmerican Mineralogist
Volume99
Issue number8-9
DOIs
Publication statusPublished - Aug 1 2014

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Keywords

  • FeCr2O4
  • Post-spinel
  • Rietveld analysis
  • crystal structure
  • high pressure
  • ophiolite
  • phase transition
  • shocked meteorite

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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