Martian surface mineralogy and geochemistry as indicators of past environmental, geochemical, and aqueous conditions

The geochemistry of the martian surface is being studied in-situ using the Curiosity rover, and the Perseverance rover is currently caching martian surface samples with the goal of returning them to Earth for laboratory analyses. The goal of this dissertation was to (1) Understand martian surface mineralogy and geochemistry using in-situ evolved gas data from the Sample Analysis at Mars (SAM) instrument on the Curiosity rover, and (2) Prepare for analyses of future martian returned samples by studying the morphology and isotopic composition of silica precipitated in the laboratory from Mars-relevant low-temperature brine solutions. In chapters 2 and 3, perchlorates, chlorides, and mixtures of these salts in Mars-analog phases were analyzed for their oxygen and hydrogen chloride (HCl) gas releases on a SAM-analog laboratory instrument in order to constrain which Cl-bearing salts are present in Gale crater. Results demonstrated that SAM HCl evolutions may be caused by chlorides (original or from oxychlorine decomposition) reacting with water-evolving phases or hydrated sulfates. Chapters 4 and 5 investigate the morphology and oxygen isotopic composition of low-temperature silica. Amorphous silica is abundant on the martian surface and surface temperatures are below 0 °C, therefore it is essential to prepare to analyze these types of martian samples for when they are returned to Earth. Cryogenic opal-A (COA), which forms in fluid veins in ice, was synthesized in the laboratory using different solution chemistries and freezing temperatures. Results demonstrated that the morphology of COA depended on the freezing temperature and solution chemistry. Martian returned samples containing COA could elucidate past climate and the chemical composition of precursor fluids. Silica will be precipitated from <0 °C brine solutions and the products will be analyzed for their triple-oxygen isotopic composition. This study was delayed due to lab closures during the Covid-19 pandemic. The purpose of this study is to determine if current paleotemperature equations apply to silica samples that form under martian conditions (i.e., <0 °C). These projects further our understanding of past martian geochemical and environmental conditions using data collected in-situ by the Curiosity rover and prepare future investigators for analyses of returned samples.