Shock-enhanced dissolution of silicate minerals and chemical weathering on planetary surfaces

This paper reports on shock-recovery experiments performed on samples of bytownite, oligoclase, and hornblende in order to assess the interrelationships between shock-activation and chemical weathering of natural materials. The three silicate minerals were recovered from peak pressures of 7.5, 16, and 22 GPa, and were subjected to analysis by optical microscopy, scanning electron microscopy (SEM), x-ray diffraction, and BET gas adsorption. The dissolution response of three major elements (silicon, aluminum, and calcium) into a pH-buffered aqueous solution was examined for the shocked and unshocked samples. The rate of mass-normalized silicon release increased for all three minerals and, in some cases, was enhanced by a factor of more than 20. Only part of this behavior was due to increased surface area; all three minerals demonstrated an enhancement in surface-area-normalized dissolution of silicon, with two- to seven-fold increases of the rate. The results imply that shock-activation may play a significant role in the chemical weathering of planetary surfaces (e.g., Mars) where impact-cratering and rock-water interactions are both important processes. Estimates of volume amounts of material shocked by impacts onto Mars suggest that the unmelted fraction of ejecta can play an important role in soil formation