A SALTY COCKTAIL ON THE ROCKS. THE EFFECTS OF BRINES ON THE DISSOLUTION, FORMATION, AND PRESERVATION OF NEAR-SURFACE MINERALS ON MARS

The abundance of salts on the surface of Mars, in soils, outcrops, veins, and meteorites, points to a history of liquid water and water loss. However, salts can also facilitate liquid water stability, by lowering the freezing point and vapor pressure, as well as deliquescing water from the atmosphere. Our lab group has been working for the past decade to determine how brines affect mineral dissolution rates and influence secondary mineral formation through laboratory experiments. Our results show that chemical weathering of pyroxene, albite, and basalt can occur in both sulfate and chloride brines, despite low activities of water, forming clays and other secondary minerals. While the low activity of water slows dissolution and alteration rates, anions and cations in solution often react to form new secondary phases, including abundant clays. Similarly, while carbonates and alunite group minerals dissolve more slowly in brines than in fresh water, they often react with the solution to form additional secondary minerals, including dolomite, chuckanovite, akaganeite, and gypsum. Often, these secondary mineral products, which formed over days to months of reaction, are observable with electron microscopy and Raman analyses, but are not detectable with XRD. Current experiments focused on characterizing sulfide-brine and clay-brine interactions and products are ongoing, but preliminary results suggest that salts in brines can readily react with ions within clay interlayers to form new minerals almost instantaneously. Therefore, brines may have played a significant role in dissolving and altering primary minerals, as well as forming and preserving secondary minerals on Mars.