Vaporization of Major Mantle Silicates: Vapor Curves for Olivine and Bronzite

Giant impacts between protoplanets during accretion exert pressures of 100’s of GPa on planetary materials, leading to melting and vaporization. Bronzite, (Mg,Fe)₂Si₂O₆, an iron-bearing pyroxene found in the upper mantle, is chemically similar to bridgmanite (silicate with perovskite structure) which makes up approximately 70% of Earth’s volume. Olivine (Mg_0.9Fe_0.1)₂SiO₄ is a major upper-mantle silicate. These two iron-bearing silicates are commonly used to represent the bulk mantle composition in planetary impact studies. We have performed shock-release and shock-stagnation experiments on the Sandia Z-Machine to measure the vapor dome and constrain the critical points for Tanzanian bronzite and San Carlos olivine. The initial shock pressures range from around 350 GPa to 700 GPa. Stagnation experiments allow the material to expand and boil before reverse-impacting a downrange window. The stagnation velocity and induced shock in the downrange window are used to determine the density of the liquid branch of the vapor dome. Defining vapor curve and critical point is essential to modeling the aftermath of giant impacts, including applications to planet formation and the origin of the Moon. We will present shock-and-release temperatures combined with our stagnation data to define the vapor dome in the equation of state.