Solubility of FeO in (Mg,Fe)SiO 3 perovskite and the post-perovskite phase transition

Abstract

Phase relations in Mg 0.5Fe 0.5SiO 3 and Mg 0.25Fe 0.75SiO 3 were investigated in a pressure range from 72 to 123 GPa on the basis of synchrotron X-ray diffraction measurements in situ at high-pressure and -temperature in a laser-heated diamond-anvil cell (LHDAC). Results demonstrate that Mg 0.5Fe 0.5SiO 3 perovskite is formed as a single phase at 85–108 GPa and 1800–2330 K, indicating a high solubility of FeO in (Mg,Fe)SiO 3 perovskite at high pressures. Post-perovskite appears coexisting with perovskite in Mg 0.5Fe 0.5SiO 3 above 106 GPa at 1410 K, the condition very close to the post-perovskite phase transition boundary in pure MgSiO 3. The coexistence of perovskite and post-perovskite was observed to 123 GPa. In addition, post-perovskite was formed coexisting with perovskite also in Mg 0.25Fe 0.75SiO 3 bulk composition at 106–123 GPa. In contrast to earlier experimental and theoretical studies, these results show that incorporation of FeO stabilizes perovskite at higher pressures. This could be due to a larger ionic radius of Fe 2+ ion, which is incompatible with a small Mg 2+ site in the post-perovskite phase.