Magnesium silicates at high dynamic loading

Research on the dynamic compression of geological materials is important for understanding composition and physical condition of the deep interior of the Earth and other planets. It also provides some data on the interaction processes related to the formation and evolution of planets. Magnesium silicates dominate in Earth's mantle and, thus, are expected to become the major phases in rocky exoplanets. In particular, enstatite Mg2[Si2O6] and forsterite Mg2SiO4 are essential constituents of Earth's mantles. Strong emphasis is put on the phase transition possibility for magnesium silicates under study. A remarkable fact is the dissociation of Mg2SiO4 into the following oxides: MgO and SiO2 (stishovite). The experiments have been carried out at a pressure value of 33 GPa, which corresponds to that in Earth's mantle at a depth of 1000 km. In this paper, the results of modeling the shock-wave loading of enstatite and forsterite as the mixtures of quartz SiO2 and periclase MgO are presented. The proposed model assumes that the components of the mixture under shock-wave loading are in thermodynamic equilibrium. The components of the material under study are considered in a phase transition region as a mixture of low- and high-pressure phases. The model is also valid for a polymorphic phase transition region. The calculations of magnesium silicates are performed with account for the polymorphic phase transition of quartz and periclase. The results are validated using the data obtained in dynamic experiments.