Thermophysical properties and phase diagrams in the system MgO–SiO2–FeO at lower mantle conditions derived from a multiple-Einstein method

Abstract

In a previous paper we showed that the multiple Einstein method is suitable to determine consistency of data on thermophysical properties and phase diagrams in the system MgO–FeO–SiO2 for upper mantle and transition zone conditions in the Earth. Here we extend this work to conditions covering the lower mantle, in the temperature range between 0 and 3000 K and pressure range between 20 and 140 GPa, with the goal to determine which data are consistent with each other. The resulting database is used to study the effect of the spin transition in ferropericlase on thermophysical properties and phase diagrams. Although trade-off is present in the model parameters due to the lack of experimental data, we show that models, reduced in complexity, can be used to study the effect of Fe3+ on these properties and phase equilibria. We show that the effect of the miscibility gap in ferropericlase, its spin transition and the valence state of Fe does not have a significant visibility in seismic density and velocities isentropes. We demonstrate that the overall composition derived by Chust et al. (J Geophys Res Solid Earth 122:9881–9920, 2018) is suitable to represent PREM and AK135 seismic data to within experimental uncertainty.