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 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. The 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 the top lower mantle dynamics and constrain pressure and temperature conditions of shocked meteorites.

Liu, Z., Liu, R., Shang, Y., Shen, F., Chen, L., Hou, X., Yao, M., Cui, T., Liu, B. and Katsura, T., Aluminum solubility in bridgmanite up to 3000 K at the top lower mantle, Geoscience Frontier, in press. doi.org/10.1016/j.gsf.2020.04.009