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 language | English |
---|---|
Pages (from-to) | 1788-1797 |
Number of pages | 10 |
Journal | American Mineralogist |
Volume | 99 |
Issue number | 8-9 |
DOIs | |
Publication status | Published - Aug 1 2014 |
Keywords
- FeCr2O4
- Post-spinel
- Rietveld analysis
- crystal structure
- high pressure
- ophiolite
- phase transition
- shocked meteorite
ASJC Scopus subject areas
- Geophysics
- Geochemistry and Petrology