Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p44a..04s&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P44A-04
Other
5220 Hydrothermal Systems And Weathering On Other Planets, 5415 Erosion And Weathering, 5464 Remote Sensing, 5470 Surface Materials And Properties, 6225 Mars
Scientific paper
CRISM spectral data collected over an unnamed 70-km-diameter impact crater in the Noachian-age southern highlands of Terra Sirenum (30°S, 158°W), Mars, indicate the presence of the acid-sulfate mineral alunite [KAl3(SO4)2(OH)6], based on diagnostic absorptions at NIR wavelengths. The USGS Tetracorder spectral shape-matching system was used to create color-coded maps of the distribution of IR-active mineral phases on the Martian surface. These maps indicate that a discontinuous, 1-km-wide, several-km-long, SE-trending band of alunite-rich material grades laterally into materials spectrally dominated by kaolinite or halloysite, and montmorillonite or partially hydrated silica. These minerals are found in layered terrain near the SW crater wall. Lava flows cover portions of the crater floor and partially embay this layered terrain. Montmorillonite or partially hydrated silica is also present in ridged material located several kilometers east of the alunite zone. Meter-scale HiRISE data indicate that the alunite occurs in a high albedo layer that is tens of meters thick and is capped in places by a spectrally neutral material. Kaolinite or halloysite occurs in polygonally cracked materials reminiscent of desiccated sediments. The observed association of minerals is consistent with advanced-argillic alteration associated with relict high-temperature hydrothermal systems, but is also compatible with the mineralogy of low- temperature, acid-saline, evaporative lacustrine deposits. Recent research indicates that alunite's NIR spectral features can be used to determine the approximate temperature at which alunite forms. CRISM alunite spectra closely match spectra of low-temp. terrestrial lacustrine alunites, based on relatively weak vibrationally-coupled absorptions at 1.43, 1.76, 2.21, and 2.32 μm. Given the observed lack of inflow channels, it is likely that the alunite was deposited in a spring-fed lake that once covered the bottom of the crater. Alunite may have formed as an alteration product of basaltic material in contact with H2SO4-rich lake water. Although oxidation of sulfides or hydrothermal H2S requires oxygen to form H2SO4, the disporportionation of SO2 that condenses in water above volcanic vents does not require an external source of oxygen and is a more likely source of aqueous sulfate for the formation of the alunite. Exploration for evidence of past aquatic life should be considered.
Clark Roger Nelson
Crowley James K.
Desborough George A.
Ehlmann Bethany L.
Gondet Brigitte
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