| 24296 |
abstract |
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 CO<sub>2</sub> (or
HCO<sub>3</sub><sup>-</sup>, CO<sub>3</sub><sup>2-</sup>) in the system. To evaluate
the effect of CO<sub>2</sub>, 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 H<sub>2</sub>CO<sub>3</sub>.
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. |