Computer simulation of the phase diagram for the MgO-SiO2 system at P - T parameters of the mantle transition zone

The paper reports an attempt to study the topologies of the phase diagram for the MgO-SiO₂ system at high pressure and temperature using computer simulation. Phase equilibria at MgSiO₃ stoichiometry is investigated, demonstrating that the invariant point Gr+Ilm+Pv is stable at 21.6 GPa and 2270 K. A thermodynamic data base for minerals in the MgO-SiO₂ system is established by supplementing the calorimetric data for low pressure phases and equations of state for low and high pressure phases with data calculated from high pressure synthesis experiments. A refined set of standard free energies of formation and phase transformations in the MgO-SiO₂ system is presented. The proposed phase diagram covers a wide range of pressure (up to 25 GPa) and temperature (up to 2500 K) and forms the basis for a geochemical interpretation of the nature of seismic discontinuites in the mantle.