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 (sub 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 + or - 500 kelvins for CaSiO (sub 3) and 7800 + or - 600 kelvins for CaO at the base of the lower mantle (136 GPa). The bulk sound velocities of CaO and CaSiO (sub 3) liquids at the core-mantle boundary are found to be 40 % lower than P-wave seismic velocity and 22 % lower than that of MgSiO (sub 3) 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.