Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p43b1400e&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P43B-1400
Other
1011 Thermodynamics (0766, 3611, 8411), 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 4470 Renormalization Group Methods, 5220 Hydrothermal Systems And Weathering On Other Planets, 6225 Mars
Scientific paper
Particle lifetime calculations utilizing olivine (Olsen and Rimstidt, 2007; Stopar et al., 2006) and jarosite (Elwood Madden et al. 2008) dissolution rates have been used to constrain the duration of aqueous environments on the surface of Mars. Previous rate experiments have shown that jarosite dissolves relatively quickly in dilute aqueous solutions leading to short particle lifetimes. However, mineralogy and bulk chemistry of outcrops containing jarosite at Meridiani Planum suggest high salinity fluids were active in the region. The goal of this study is to determine the effects of high salinity (low activity of water) on jarosite dissolution rates. K-jarosite was synthesized using the methods of Baron and Palmer (1996) and characterized using powder X-ray diffraction, BET surface area analysis, transmission electron microscopy, and atomic force microcopy. Dissolution experiments were conducted by adding 0.5 g K- jarosite to 500 g ultrapure water at 293K. Samples were collected from the continuously-stirred batch reaction at predetermined intervals and filtered using 0.2 micron filters. K+ concentrations in the resulting supernatants were measured using atomic adsorption spectroscopy to determine the rate of jarosite dissolution. Jarosite dissolution experiments in halite saturated brine result in dissolution rates over one order of magnitude slower than similar experiments conducted in dilute solutions. Dissolution in ultrapure water proceeds at log k= -8.5. Jarosite dissolution in halite saturated brine is significantly slower: log k = -10. Using a shrinking sphere model to calculate particle lifetimes, the lifetime of a 10 micron diameter jarosite particle is extended from 1-2 years in dilute solutions to 100 years in high salinity brine. This suggests that while jarosite is an ephemeral phase in dilute solutions, it may persist for significantly longer time periods in high salinity waters, such as those interpreted at Meridiani Planum based on bulk chemistry and evaporite minerals present within the outcrops. However, even in high salinity fluids, jarosite would not be preserved in aqueous systems lasting thousands to millions of years.
Elwood Madden Megan E.
Madden Andrew S.
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