Lower Mantle Melting: Experiments and Thermodynamic Modeling in the System MgO‐SiO2

Abstract

AbstractCharacterizing and modeling melting relations in the system MgO‐SiO2 at lower mantle pressures rely on the location of the eutectic points for MgO‐MgSiO3 and MgSiO3‐SiO2. While at an uppermost lower mantle pressure there is general consensus on the eutectic composition in the former, large discrepancies exist for MgSiO3‐SiO2 from experiments in the diamond anvil cell, ab‐initio simulations and models built on them. In order to address this discrepancy, we have performed multi‐anvil press experiments at GPa for Mg4Si6O16 and Mg3Si7O17 at temperatures of K and K. In the experiments at K, we observe the presence of partial melt. The recovered Mg4Si6O16 sample shows SiO2 stishovite as the liquidus phase, and electron microprobe analysis of the quenched melt determines as the eutectic composition. We fit a thermodynamic model to describe the melting relations in the MgO‐SiO2 system, and extrapolate to core‐mantle boundary pressure. At 136 GPa, we predict that the eutectic points have moved further away from enstatite composition, and solidus temperatures remain similar for MgO‐MgSiO3 and MgSiO3‐SiO2.