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


Abstract

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.


The Al2O3 and MgSiO3 contents, respectively, in bridgmanite and corundum as a function of temperature. Dashed lines are thermodynamics calculation results.


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Liu et al. Gerscience Frontiers 2020 Jou
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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