20-EPN-046: iVOL – Impact-induced volatile release from calcium sulphates anhydrite and gypsum re-investigated in an open system by two-stage light-gas gun impact experiments
Virtual visit by Christopher Hamann and Robert Luther of Museum für Naturkunde Berlin (Germany), to TA2.7 Light Gas Gun Laboratory, University of Kent (UK)
Dates of visit: 01 September 2021 – 01 May 2022
Clarifying the response of volatile-bearing materials such as sulphates and carbonates to hypervelocity impacts is important, as it relates to the potential modification of planetary atmospheres by release of volatiles. However, most previous studies aimed at delineating the shock behaviour of sulphates and carbonates were done using confined or ‘closed’ setups (e.g., shock-recovery experiments) that hampered formation and escape of volatile species resulting from shock compression and subsequent release. Here, we focus on calcium sulphates, which are abundant on Earth and Mars and are likely targets of hypervelocity impacts.
By using the two-stage light-gas gun at the University of Kent Light Gas Gun Laboratory, we investigated the response of gypsum (CaSO4⋅2H2O) and anhydrite (CaSO4) to hypervelocity impacts in a fully unconfined or ‘open’ system that allowed impact-induced formation and escape of volatiles such as H2O and SO2/SO3 as well as recovery of shocked materials. By petrographic investigation of shocked, solid ejecta and materials lining the impact craters, we find that dehydration of gypsum to anhydrite proceeds via bassanite (CaSO4⋅0.5H2O) and results in distinct changes of microtextures (e.g., dehydration cracks) and Raman spectra (e.g., weakening of water Raman bands). In addition, further devolatilization of sulphur-bearing species from anhydrite or solid dehydration products as well as melting is suggested from a distinct Ca-enrichment in µXRF element distribution maps and certain microtextures (e.g., spherical objects resembling melt spherules) observed under the SEM, respectively. These characteristics may be used to identify shocked calcium sulphates among terrestrial or extraterrestrial (e.g., future Martian) samples.
