SHOCK INDUCED VAPORIZATION OF ANHYDRITE CaS04 AND CALCITE CaCO3

Discovery of abundant anhydrite (CaS04) and gypsum (CaS0+2HzO) in the otherwise carbonate sediments comprising the upper portion of the rocks contained within the Chicxulub impact crater has prompted research on the shock-induced vaporization of these minerals. We use a vaporization criterion determined by shock-induced entropy. We reanalyze the shock wave experiments of Yang [ 11. He shocked 30% porous anhydrite and 46% porous calcite. Post-shock adiabatic expansion of the sample across a 5 mm-thick gap and then impact upon an aluminum witness plate backed by LiF window that is monitored with a VISAR. Reanalysis uses Herrman’s P-a model [2] for porous materials, and a realistic interpolation gas equation-of-state for vaporization products. Derived values of the entropies for incipient and complete vaporization for anhydrite are 1.65&O. 12 and 3.17&O. 12 kJ(kg.K)-‘, and for calcite these are 0.99+0.11 and 1.93f0.11 kJ(kg.K)-i. Corresponding pressures for incipient and complete vaporization along the Hugoniot of non-porous anhydrite are 32.5 a.5 and 122+13 GPa and for non-porous calcite are 17.8 +2.9 and 54.M.3 GPa, respectively. These pressures are a factor of 2-3 lower than reported earlier by Yang.