Shock vaporization of anhydrite and global effects of the K/T bolide

Abstract

Shock vaporization experiments were carried out for 30% porous anhydrite up to 76 GPa. Shocked fully or partially vaporized samples interact with overlying LiF windows whose velocity histories are monitored using a velocity interferometer to obtain pressure bounds for incipient and complete vaporization for CaSO_4. Experimental data and thermodynamic calculations indicate that these shock pressures are 81 ± 7 and 155 ± 13 GPa for crystal anhydrite, and 27 ± 1 and 67 ± 6 GPa for porous anhydrite, respectively. A one-dimensional finite-difference code was used to simulate the measured velocity profiles. The vaporized products can be described by a simple Grüneisen thermal equation of state where the effective Grüneisen parameter varies from 1.5 to 0.73 upon release from 76 to 25 GPa. Using the above criteria, and recent lithic models of the impact site, the mass of degassed S has been estimated from the Chicxulub impact. For asteroids of 10 and 20 km in diameter impacting the Earth at 20 km/s, the mass of degassed S in SO_2 or SO_3 is found to be 0.5 × 10^(17) to 2 × 10^(17) g. Simple extrapolation of Sigurdsson's [H. Sigurdsson, Assessment of the atmospheric impact of volcanic eruptions, in: V.L. Sharpton, P.D. Ward (Eds.), Global Catastrophes in Earth History: An Interdisciplinary Conference on Impact, Volcanism, and Mass Mortality, Geol. Soc. Am. Spec. Pap. 247 (1990) 99–110.] formula yields a global cooling prediction of ≳10°C.

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