Fluid-Evaporation Records Preserved in Meridiani Rocks

We have shown earlier that the high SO3/Cl ratios found in secondary mineral assemblages in shergottite GRIM glasses (Gas-Rich Impact-Melt) likely resulted from interactions of regolith materials with sulfate-rich (and Cl-poor) solutions. The low SO3/Cl ratios determined in secondary salts in nakhalite fracture-fillings presumably formed by rock interactions with chloride-rich (and SO4-poor) solutions near Mars surface. The SO3 and Cl abundances determined by APXS in abraded rocks (RAT) from Endurance, Fram and Eagle craters indicate that these salt assemblages likely formed by evaporative concentration of brine fluids at Meridiani. The SO3/Cl ratios in the abraded rocks are examined here, instead of their absolute abundances, because the abundance ratios might provide better guide-lines for tracking the evolution of evaporating fluids at Meridiani. The SO3/Cl ratios in these samples, in turn, might provide clues for the mobile element ratios of the altering fluids that infiltrated into the Meridiani rocks.