Shock temperature measurements in Mg2SiO4 and SiO2 at high pressures

Temperatures in the high pressure shock state have been determined by measurement of optical radiation from pure samples of forsteritc (Mg2 SiOn), a-quartz, and fused silica. Shock waves of known amplitude were produced by tantalum flyer impact using a two-stage light gas gun. Shock pressures in the ranges 150-175 GPa and 70-115 GPa for Mg: SiOn and SiO2 respectively were achieved, and temperatures in the range 4500-6800 K were measured. The observed temperatures in Mg: SiOn are consistent with the occurrence of a shock-induced phase transition with a transition energy of • 1.5 MJ/kg, Measured Hugoniot temperatures versus pressure in both fused and crystalline SiO: shocked to the stishovite regime suggest the occurrence ofa previously unknown transition, beginning at pressures of approximately 107 GPa and 70 GPa for a-quartz and fused quartz, respectively. The energies and temperatures appear to be consistent with the onset of melting of stishovite under shock loading.