HR: 15:00h
AN: P13B-06    [Abstracts]
TI: Mineral Composition and Abundance of the Rocks and Soils at Gusev and Meridiani from the Mars Exploration Rover Mini-TES Instruments: Implications for Aqueous Processes
AU: * Christensen, P
EM: phil.christensen@asu.edu
AF: Arizona State University, Dept. of Geological Sciences, Tempe, AZ 85284 United States
AB: The Mini-TES instruments on Spirit and Opportunity have studied the mineral composition and abundance of the outcrops, rocks, spherules, and soils at Gusev Crater and the Meridiani Plains. At Gusev undisturbed soil spectra closely match MGS TES bright-region dust spectra, with features interpreted to be due to minor carbonates and bound water. Dark-toned soils observed on rover-disturbed surfaces are likely derived from rocks and has a derived mineralogy, with uncertainties of 5-10 percent, of 45 percent pyroxene (20 percent Ca-rich pyroxene, 25 percent pigeonite), 40 percent sodic/intermediate plagioclase, and 15 percent olivine (Fo45 ñ~10). Rocks have complex spectra that are influenced by coatings and atmospheric downwelling radiance, as these high-thermal-inertia rocks are typically colder during the day than the atmosphere. Their Mini-TES spectra are consistent with olivine-rich basalts with varying degrees of dust and other coatings. Aeolian drift material has a unique spectral character with higher oxide abundances than disturbed soil. One (or possibly two) spectrally distinct coatings are observed on rocks, a possible indicator of the interaction of water, rock, and airfall dust. At Meridiani, the Mini-TES has identified coarse crystalline hematite and olivine basalt sands as predicted from orbital TES spectroscopy. Light-toned outcrops of aqueous origin exposed in crater walls are composed of 20 to 40 percent Mg and Ca sulfates, a high-silica component that is modeled as glass/feldspar/sheet silicates (~20-30 percent), and hematite. The Fe sulfate jarosite is not reliably identified in Mini-TES spectra. The mm-sized spherules appear from analysis of Mini-TES spectra to be dominated by hematite, with no other components detected. Basaltic materials have more plagioclase than pyroxene, contain olivine, and are similar in inferred mineral composition to basalt mapped by TES from orbit. Bounce Rock is dominated by clinopyroxene and is closer in inferred mineral composition to the basaltic SNC meteorites. Bright wind streak material downwind of Eagle crater closely matches the IR spectrum of global dust, suggesting that these materials were deposited as fallout from global dust storms as predicted by Veverka and colleagues. The occurrence of waterlain rocks covered by olivine, pyroxene, and feldspar in basaltic sands suggests a significant change from an aqueous environment at the time the rocks were deposited to one dominated by physical weathering. The occurrence of basalts and olivine basalts throughout much of the equatorial and mid-latitude regions suggests that chemical weathering may have been a relatively minor process, at least in low- to mid-latitudes, throughout much of martian history. Thus, the presence of a body of water may represent a relatively brief, localized phenomenon early in Mars history.
DE: 5410 Composition
DE: 5464 Remote sensing
DE: 5480 Volcanism (8450)
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting