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

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 degrees C. Pure perovskites with 10 and 15 mol % FeSiO3 can only be synthesized above 1525 degrees C and 2072 degrees 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 Mossbauer spectroscopic and X my diffraction studies revealed that laser-heated samples with more than 10 mol % FeSiO3 invariably contained magnesiowustite. The coexistence of magnesiowustite 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.