Maximum solubility of FeO in (Mg, Fe)SiO3‐perovskite as a function of temperature at 26 GPa: Implication for FeO content in the lower mantle

Abstract

We have explored phase relations in the fundamental ternary system MgO‐FeO‐SiO2 at lower mantle pressure (26 GPa) via synthesis experiments on the join MgSiO3‐FeSiO3. The maximum solubility of FeO in (Mg,Fe)SiO3 perovskite as a function of temperature has been determined in the multianvil apparatus in the temperature range of 1150–1740°C. Pure perovskites with 10 and 15 mol % FeSiO3 can only be synthesized above 1525°C and 2072°C, respectively, at 26 GPa. Synthesis experiments were also conducted in a laser‐heated diamond anvil cell to resolve a previous discrepancy concerning the maximum solubility of FeO in (Mg,Fe)SiO3 perovskite determined by different high‐pressure apparatus. Both Mössbauer spectroscopic and X ray diffraction studies revealed that laser‐heated samples with more than 10 mol % FeSiO3 invariably contained magnesiowüstite. The coexistence of magnesiowüstite with relatively lower FeO content perovskite results from chemical disequilibrium process caused by the large temperature gradient in the laser‐heated samples. Finally, we conclude that the maximum FeO content at the top of the lower mantle is about 12 mol % for a perovskite‐dominated lower mantle, along a 2000‐K lower mantle geotherm.