Phase relations in the system MgO-FeO-SiO2 to 50 GPa and 2000°C: An application of experimental techniques using multianvil apparatus with sintered diamond anvils

摘要

Phase relations in the system MgO-FeO-SiO2 were investigated between 22 and 47 GPa at 1500°C and 2000°C using multianvil apparatus with sintered diamond anvils. Synthesized samples were analyzed with electron microprobe, analytic transmission electron microscopy, and X-ray diffraction using synchrotron radiation. Univariant compositions of (Mg,Fe)SiO3 perovskite and (Mg,Fe)O magnesiowiistite coexisting with SiO2 stishovite were determined as functions of pressure and temperature. The maximum iron solubility in perovskite corresponding to the univariant composition gradually increases with increasing pressure and temperature to be more than 30 mol % at 2000°C and pressures above 40 GPa, and a significant pressure effect was found in Fe-Mg partitioning between perovskite and magnesiowiistite in pressures between 22 and 3.5 GPa. The iron content of magnesiowiistite dramatically increases from 50 to greater than 90 mol % with increasing pressure, and the Fe-Mg distribution coefficients between perovskite and magnesiowiistite, KD = (^le/^Mg)/C^eW/^g), decrease to less than 0.05., This significant pressure effect in Fe-Mg partitioning causes strong concentration of ferrous iron in magnesiowiistite with increasing depth in the lower mantle.