Other
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p11c0706m&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P11C-0706
Other
1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 3616 Hydrothermal Systems (0450, 1034, 3017, 4832, 8135, 8424), 5415 Erosion And Weathering, 6225 Mars
Scientific paper
The detection of ferric sulfates and silica-rich deposits with the Mars Exploration Rovers is consistent with mineral deposition in acid aqueous environments. By analogy with terrestrial volcanic settings (e.g. Yellowstone National Park), oxidation of dissolved H2S on Mars should have led to the production of sulfuric acid. Speciation models for martian volcanic gases reveal elevated H2S abundances in reduced mantle-derived emanations; and experimental data show efficient H2S oxidation by dissolved O2. On Mars, volcanic and impact-generated H2S could have been dissolved in cold/hot subsurface and spring waters, in atmospheric aerosols, and in surface water reservoirs away from volcanic/impact events. H2S could then be oxidized by O2 that forms rapidly in atmospheric photochemical processes and in strong impacts. We used kinetic-thermodynamic models to evaluate rates and chemical/mineralogical pathways of aqueous H2S oxidation on ancient Mars. The models consider dissolution rates of primary (basaltic) and secondary minerals, mineral grain sizes, supply of H2S and O2, kinetics of H2S oxidation [ Millero and Hershey, 1987], and mineral precipitation at variable water/rock ratios and atmospheric O2 pressures [cf. Zolotov and Mironenko, 2007, JGR-Planets, E07006]. The models were applied for volcanic springs, non-volcanic lakes, and atmospheric aerosols. Results show rapid sulfuric acid production even at the current O2 pressure and temperature of 273 K. Typically, H2S-bearing fluids oxidize faster than solution neutralizes through mineral dissolution. Although oxidation rate depends on several parameters, major oxidation occurs within a year. A continuous supply of H2S into near-surface fluids causes pervasive acid alteration of basalts. High water/rock ratios (e.g., due to discharge of solutions from springs) favor leaching of elements and cause deposition of relatively insoluble amorphous silica and Ti oxide. Subsequent freezing and/or evaporation of acid or neutralized spring fluids leads to deposition of sulfates. Degassing and oxidation of H2S could explain net addition of S to martian basaltic materials, and the formation of ferric sulfates and silica-rich deposits.
Mironenko Mikhail V.
Zolotov Mikhail Yu.
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