Relative shock effects in mixed powders of calcite, gypsum, and quartz; a calibration scheme from shock experiments

A systematic experimental shock study of calcite, gypsum, and quartz powders mixed 1:1:1 was carried out in order to calibrate shock pressures in naturally shocked carbonates and sulfates to shock effects in quartz. Shock recovery experiments were performed by the multiple reverberation technique at pressures between 9.9 and 47.1 GPa. Shock effects were analyzed petrographically and by electron microprobe analysis. Gypsum is rapidly and efficiently disaggregated at modest pressures (approximately 24.3 GPa). Calcite is surprisingly stable and retains its characteristic high birefringence at pressures as high as 47 GPa. Modest evidence for melting is observed in the sulfate-dominated matrix of the 24.3 GPa sample and at higher pressures. However, no substantial compositional gradients associated with specific clasts were observed that would be suggestive of S-depletion (thus partial loss of SO (sub 2) ) of specific gypsum grains or of Ca-enrichment (thus partial loss of CO (sub 2) ) associated with carbonate grains. Deformation effects observed in these shock experiments on calcite and gypsum are solid-state reactions and, by comparison to solid-state shock effects in quartz from the same experiments, provide a calibration scheme for shock effects in naturally shocked rocks. However, the effects will only be observable if those effects have not been overprinted by subsequent processes such as thermal annealing or alteration.