Impact-generated hydrothermal alteration on Early Mars in presence of CO2

Schwenzer, S. P. and Kring, D. A. (2009). Impact-generated hydrothermal alteration on Early Mars in presence of CO2. In: 72nd Annual Meteoritical Society Meeting, 13-18 Jul 2009, Nancy, France.



Impact-generated hydrothermal systems may have caused widespread alteration of the crust on early Mars. We previously explored the range of alteration products using several Martian meteorites as crustal proxies: LEW88516, Dhofar 378, Chassigny, and Nakhla. Overall, the dominating alteration phases are oxides, hydroxides, clay minerals, and other hydrous silicates. Our results match well with the hydrous silicates (nontronite, chlorite) observed by OMEGA and CRISM. The two most recent findings by CRISM are carbonates and serpentine. While the latter is formed in our calculations from all olivine-rich starting compositions (LEW88516, Chassigny), carbonates require CO2 (or HCO3-, CO32-) in the system. To evaluate the effect of CO2, we conducted new calculations with ALHA84001 and maskelynite as starting compositions by exposing them to the same brine used before and, in a second set of calculations, with the addition of 0.5 mol H2CO3. We are using ALHA84001, because its secondary carbonates provide a unique opportunity to compare model and mineralogical data. Moreover, it is the only sample of the ancient Martian crust within the suite of Martian meteorites.

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