High Pressure And High Temperature Study In The MgO-FeO And Fe-Ni-S Systems And Their Geophysical Implications

MgSiO₃ perovskite and ferropericlase (Mg,Fe)O are generally considered as the most dominant components in the Earth's lower mantle. Experimental measurements of P-V-T properties of Earth-related phases are crucial for developing accurate mineralogical and compositional models of the Earth's interior. Two stage gas-gun and multi-anvil apparatus are used to simulate high pressure and high temperature condition. This study focuses on the P-V-T equation of state and phase transition of (Mg,Fe)O at high pressure and high temperature. We also examine the phase relations of the MgO-FeO and Fe-Ni-S system at high pressure and high temperature and their implications in the composition of the Earth's interior. Our study improves our understanding mineralogical and compositional models of the Earth's interior, and also provides the explanations for the scattering of seismic waves and change in velocity gradient found in the lowermost mantle.The main achievements in this study are as followings:(1) We introduce the experimental methods to synthesize large bulk MgSiO₃ perovskite and ferropericlase (Mg,Fe)O using Piston-cylinder and Mutli-anvil apparatuses, and the synthesized samples were analyzed by micro electronic probe, Raman spectrum, and X-Ray diffraction. This makes it possible to do shock wave experiments with the large bulk MgSiO₃ perovskite and ferropericlase (Mg,Fe)O as starting materials.(2) We report new shock-compression data for single-crystal MgO at 114 and 192 GPa. Our data together with the existing shock-wave data revealed a discontinuity at 170±10 GPa along the MgO Hugoniot. The estimated temperature at the discontinuity is about 3000±400 K, far too low to be melting. The discontinuity gives a volume increase of 1.9%, consistent with a phase transition from a NaCl structure (B1) to a high-temperature phase (most likely a NiAs-type hexagonal B8 phase) along the MgO Hugoniot. Our results add to fundamental understandings of the behavior of MgO, one of the most...