The Principal Hugoniot of Forsterite to 950 GPa

Forsterite (Mg2SiO4) single crystals were shock compressed to pressures between 200 and 950GPa using independent plate-impact steady shocks and laser-driven decaying shock compression experiments. Additionally, we performed density functional theory-based molecular dynamics to aid interpretation of the experimental data and to investigate possible phase transformations and phase separations along the Hugoniot. We show that the experimentally obtained Hugoniot cannot distinguish between a pure liquid Mg2SiO4 and an assemblage of solid MgO plus liquid magnesium silicate. The measured reflectivity is nonzero and increases with pressure, which implies that the liquid is a poor electrical conductor at low pressures and that the conductivity increases with pressure. Plain Language Summary Hypervelocity impacts are an important process for planetary and moon formation and evolution. These impact events generate pressures of millions of atmospheres. Forsterite (Mg2SiO4) is the magnesium end-member of the olivine series and is a major constituent of the Earth's mantle and likely other terrestrial planets including the recently discovered super-Earths. Here we used Sandia National Laboratories Z Machine and the OMEGA Laser Facility at the University of Rochester to shock compress forsterite to extreme pressures and temperatures. The experiments provide data showing the relationship between pressure, density, and temperature that can be used to construct a model of forsterite's behavior at extreme conditions. Improved knowledge of the properties of forsterite at the extreme pressures created in impacts or in the interiors of super-Earths will help us better understand the formation and interior structure of moons and planets.