Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p12a..08b&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P12A-08
Physics
[5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
Evaporitic processes have been responsible for at least some of the sulfates and carbonates seen on the Martian surface (e.g. [Clark et al., 2005; McLennan et al., 2005; Squyres & Knoll, 2005]). Subsurface water charged with ions due to the dissolution of basalt and interaction with atmospheric CO2 and sulfur gases would have had the necessary chemistry to produce large quantities of evaporitic salts (e.g.[Bullock & Moore, 2004; Bullock et al., 2004; Tosca et al., 2005]). In the present work, we numerically modeled the formation of evaporites on Mars, using relevant laboratory work to constrain the calculations. Previously, we produced Mars-analog evaporites in the laboratory by desiccating brines formed under simulated Mars surface conditions [Moore et al., 2009]. The evaporites were created under two different conditions: Evaporation of brines at 3°C and 10 mbar of CO2, and evaporation of brines at 3°C and 10 mbar of CO2 with added acidic gases (100 ppm SO2, 10 ppm NO2, and 10 ppm HCl) to simulate an atmosphere rich in volcanic volatiles. We analyzed these evaporite products using IR spectroscopy and SEM microprobe. In general, Ca-sulfates dominated the precipitate mineralogy from the present-day Mars simulations, and for more acidic conditions, Mg-sulfates dominated, although both phases were observed in the precipitated products. In order to illuminate the actual formation processes of evaporites on Mars, we modeled the evaporation and the freezing/sublimation of brines under a wider range of conditions appropriate to Mars. Thermodynamic calculations using standard packages such as PHREEQ and Geochemist’s Workbench usually produce a large number of spurious species that are kinetically inhibited in natural settings. Therefore, using laboratory-derived results to realistically constrain precipitation products is essential for understanding the formation of evaporites on Mars. Our modeling results are quantitatively compared with the sulfates characterized at the Meridiani outcrops by MER Opportunity [Clark et al., 2005], just beneath the surface in the Columbia Hills by MER Spirit [Haskin et al., 2005], in the interior layered deposits of Valles Marineris [Bibring et al., 2005] and in the north polar dune fields by MEX OMEGA [Langevin et al., 2005]. Starting with brines at higher pH (6-8), we also compare model results with the carbonates seen in Nili Fossae by MRO CRISM [Ehlmann et al., 2008] and the CaCO3 seen by the Phoenix Lander [Boynton et al., 2009]. This work was supported by NASA MFRP grant NNX07AR68G to MAB, and a NASA PG&G grant to JMM. Bibring, J.-P., et al., Science 307, 1576-1581, 2005. Boynton, W. V., et al., Science 325, 61-64, 2009. Bullock, M. A., & J. M. Moore, GRL, 31, 2004 Bullock, M. A., et al., Icarus, 170, 404-423, 2004. Clark, B. C., et al., EPSL, 240, 73-94, 2005. Ehlmann, B. L., et al., Science, 322, 1828-1832, 2008. Haskin, L. A., et al., Nature, 436, 66-69, 2005. Langevin, Y., et al., Science, 307, 1584-1586, 2005. McLennan, et al., EPSL, 240, 95-121, 2005. Moore, J. M., et al., submitted to JGR, 2009. Squyres, S. W., & A. H. Knoll, EPSL, 240, 1-10, 2005. Tosca, N. J., et al., EPSL, 240, 122-148, 2005.
Bullock Mark Alan
Moore Jeffery M.
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