Melting of CaO and CaSiO3 at Deep Mantle Condition Using First Principles Simulations

Abstract:

Accurate prediction of melting temperatures of major mantle minerals at high pressures is important to understand the Hadean Earth as well as to explain the observed seismic anomalies at ultra-low velocity zone (ULVZ). To further investigate the geophysical implications of our recent first principles study of molten CaO and CaSiO^­₃, we calculated the melting temperatures of the corresponding solid phases by integrating the Clausius-Clapeyron equation. The melting behavior of their high-pressure phases can constrain the lower mantle solidus. Our calculations show melting temperature of 5700 ± 500 kelvins for CaSiO₃ and 7800 ± 600 kelvins for CaO at the base of the lower mantle (136 GPa). The bulk sound velocities of CaO and CaSiO₃ liquids at the core-mantle boundary are found to be 40 % lower than P-wave seismic velocity and 22 % lower than that of MgSiO₃ liquid. With substantial decrease of melting temperature by freezing point depression and iron partitioning, the partial melting of multi-component silicate and its gravitational buoyancy at ULVZ cannot be ruled out.