Investigation of Shocked Basalts from Vargeão Dome and Vista Alegre: Implications for the Search for Life on Mars

Impact craters represent excellent astrobiological targets for planetary exploration missions to Mars. The impact of an asteroid or comet into a crystalline, H2O-bearing target may result in development of a hydrothermal system and increase the habitability of the substrate for the colonization of endolithic microorganisms. Given that Mars’ surface is covered by cratered basaltic rock, this study investigated target rocks and impact breccias from Vargeão Dome and Vista Alegre impact structures that formed in basalt in the Paraná Basin of Brazil. Utilizing petrography and micro-X-ray diffraction (μXRD), the degree of shock metamorphism in plagioclase was quantitively determined. Measuring the full-width-at-half-maximum of diffraction peaks reveals increased strain-related mosaicity. This is correlated with increased optical evidence of deformation. Density and porosity results reveal trends that support conclusions from previous work on different rock types, whereby, increased shock level appears to result in greater porosity. Optical microscopy, electron microprobe analysis, and μXRD were used to investigate hydrothermal alteration in the Vista Alegre crater and differentiate between pre- and post-impact hydrothermalism. We confidently verify that shocked samples within the Vista Alegre impact structure are altered by impact-induced hydrothermal activity. This alteration is distinct from that occurring outside the impact structure