Thermodynamics of shock vaporization/devolatilization of volatile-bearing rocks and its experimental investigation

In this article we first review the roles of hypervelocity impacts in volatile partitioning on planetary surfaces and thermodynamics of shock vaporization/devolatilization of geologic materials. Impact experiment in an open system is essential to accurately estimate the shock pressure required for incipient vaporization/devolatilization, and we introduce a newly-developed open system experimental technique applied to two-stage light gas guns. This experimental apparatus allows us to measure impact-generated gases with a mass spectrometer at the same geometry of natural impacts with a limited risk of chemical contamination from the gun operation. The threshold pressures of vaporization/devolatilization for halite and gypsum were measured to be 1831 GPa and ＜11 GPa, respectively. The new open system method is expected to serve as a powerful tool to explore the nature of shock vaporization/devolatilization of geologic materials. ［hypervelocity impacts, celestial collisions, shock vaporization, shock devolatilization, two-stage light gas gun, mass spectrometry]