Implications for the aqueous history of southwest Melas Chasma, Mars as revealed by interbedded hydrated sulfate and Fe/Mg-smectite deposits

Using visible and near infrared data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), we identified a sequence of hydrated sulfates and Fe/Mg-smectites in southwest Melas Chasma. Specifically, these hydrated sulfate and semectite deposits are interbedded and have been highly deformed. Equilibrium thermodynamic calculations of coupled basalt weathering and fluid evaporation predict that sequential formation of Fe/Mg-smectites and sulfate evaporites in similar quantities, as observed in the interbedded smectite-sulfate sequences, is chemically plausible. The Fe/Mg-smectite-sulfate deposits may have thus formed through in situ basalt weathering and fluid evaporation, although an origin involving repeated cycles of transport and deposition of detrital clays by a neutral fluid containing Mg and SO4 and subsequent evaporation cannot be ruled out. If the Fe/Mg-smectites are authigenic, the Hesperian (or younger) age Melas Chasma would have experienced prolonged periods with near-surface water, providing potentially habitable conditions.