Shock temperatures in anorthite glass

Summary. Temperatures of CaA12Si208 janorthite glass) shocked to pressures between 48 and I17GPa have been measured in the range from 2500 to 5600 K, using optical pyrometry techniques. The pressure dependence of the shock temperatures deviates significantly from predictions based on a single high-pressure phase. Either a variable specific heat, or the existence of three phase transitions, at pressures of about 55, 85 and l00GPa and with transi-tion energies of about 0.5 MJ kg- ' each (- 1.5 MJ kg- ' total) can explain the shock-temperature data. The proposed phase transition at 100 GPa can possibly be identified with the stishovite melting transition. Theoretical models of the time dependence of the thermal radiation from the shocked anorthite based on the geometry of the experiment and the absorptive pro-perties of the shocked material yield good agreement with observations, indicating that it is not necessary to invoke intrinsic time dependences to explain the data in many cases. Observed time dependences were used to calculate absorption coefficients of the shocked material of from about 2 mm- ' to greater than 24mm- '- an increasing function of shock pressure. The assumption that the shocked material radiates as a black body is sup-ported by the theoretical model, and by the close agreement between measured and calculated black body spectral radiance as a function of wavelength