Abstract

Valence, spin states, and crystallographic sites of Fe in (Mg,Fe)SiO3 perovskite were investigated using energy-domain 57Fe-synchrotron Mössbauer spectroscopy and powder X-ray diffraction up to 86 GPa. The volumes of Fe3+-bearing perovskite in this study are slightly smaller than those of Mg end-member perovskite. Our Mössbauer data suggest that Fe3+ prefers A sites coupled with Mg vacancies, which is consistent with previous data at ambient conditions. Fe3+ in the A site remains in a high-spin state up to 86 GPa, and some fraction of the A site is occupied by Fe2+ at pressures above 30 GPa. Fe2+ in the A sites is also in a high-spin state up to 86 GPa. The coupled substitution from Mg2+ to a high-spin state of Fe3+ and Mg2+ vacancy would make the volume of perovskite smaller than that of Mg end-member perovskite. If the lower mantle is saturated in silica, perovskite containing high-spin Fe3+ in A site has a higher density. Such silica oversaturated regions could sink by the density difference.

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