On the Timescale of Magma Ocean Solidification and Its Chemical Consequences: 1. Thermodynamic Database for Liquid at High Pressures

Abstract

We present a new method to construct an internally consistent thermodynamic model using a compilation of high-pressure melting experiments. The steepest descent method and Monte Carlo sampling are combined to constrain all model parameters simultaneously instead of determining each parameter sequentially from relevant experiments. Our approach is applied to the published melting experiments on mantle materials to obtain the thermodynamic parameters of the MgO-FeO-SiO2 ternary system. Inversion with the subsets of experimental data is conducted as well to investigate the source of discrepancy among existing studies, and the key parameters are found to be the thermal expansivity of SiO2 and the excess volume of mixing between MgO and SiO2. Mixing between FeO and SiO2 is only constrained with large uncertainty, which could also imply that oxides with low concentrations have minimal effects on melting. Constraining the thermodynamics of MgO and SiO2 will be important for a better understanding of mantle melting at high pressures.