Aluminum solubility in bridgmanite up to 3000 K at the top lower mantle

The temperature dependence of the Al₂O₃ solubility in bridgmanite has been determined in the system MgSiO₃-Al₂O₃ at temperatures of 2750-3000 K under a constant pressure of 27 GPa using a multi-anvil apparatus. Bridgmanite becomes more aluminous with increasing temperatures. A LiNbO₃-type phase with a pyrope composition (Mg₃Al₂Si₃O₁₂) forms at 2850 K, which is regarded as to be transformed from bridgmanite upon decompression. This phase contains 30 mol% Al₂O₃ at 3000 K. The MgSiO₃ solubility in corundum also increases with temperatures, reaching 52 mol% at 3000 K. Molar volumes of the hypothetical Al₂O₃ bridgmanite and MgSiO₃ corundum are constrained to be 25.95±0.05 and 26.24±0.06 cm³/mol, respectively, and interaction parameters of non-ideality for these two phases are 5.6±0.5 and 2.2±0.5 KJ/mol, respectively. The increases in Al₂O₃ and MgSiO₃ contents, respectively, in bridgmanite and corundum are caused by a larger entropy of Al₂O₃ bridgmanite plus MgSiO₃ corundum than that of MgSiO₃ bridgmanite plus Al₂O₃ corundum with temperature, in addition to the configuration entropy. Our study may help explain dynamics of the top lower mantle and constrain pressure and temperature conditions of shocked meteorites.