Physics
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusm.p22a..02c&link_type=abstract
American Geophysical Union, Spring Meeting 2004, abstract #P22A-02
Physics
5410 Composition, 5464 Remote Sensing, 6225 Mars
Scientific paper
The Spirit rover has investigated the geochemistry and mineralogy of the Gusev crater site using in situ Alpha Proton X-Ray, Mossbauer, visible, and infrared spectroscopy. The Gusev site is covered with angular to sub-rounded rocks that are typically less than 1 m in maximum dimension. More than 90 percent of these rocks are dark-toned, with the remainder being lighter-toned rocks that may predominantly be dark rocks with a thin (10's of microns) coating of easily removed fines. APXS analysis has been obtained of a rock (Adirondack) following the removal by grinding of the surface dust and the upper few mm of the rock surface. These data give a modal mineralogy corresponding to olivine basalt. High quality Mini-TES data have not been obtained of a completely dust-free rock surface. The Mini-TES data of Adirondack do show long wavelength (15-25 microns) absorptions due to olivine of composition ~Fo60. All of the rocks observed are very compositionally homogeneous in the Mini-TES spectra. These findings are consistent with the detection of olivine-bearing basalt at this site from orbital TES infrared spectroscopy. Mossbauer spectra of Adirondack show the presence of forsteritic olivine and magnetite, with possible pyroxene. The soils at Gusev are a mixture of reddish fine-grained to sandy materials, granular-sized particles that occur in ripple forms, and minor pebbles. Mini-TES spectra of the soil show an excellent match to the TES spectra of high-albedo, fine-grained material found in regional bright regions that is interpreted to be windblown dust. This agreement suggests at least the uppermost layer of the soil at Gusev has been accumulated from airfall dust. By analogy with prior analysis of TES data these materials contain several percent carbonate, minor bound water, and a framework silicate interpreted to be either feldspar or zeolite. APXS spectra show similar oxide abundances to those determined for the Pathfinder site, except for higher MgO, and lower total iron. The preliminary potassium abundances are lower than predicted from orbital GRS data. The material that fills small hollows is finer-grained than the surrounding soils based on temperatures from Mini-TES, and may be predominantly airfall dust. To date there is no evidence from the mineralogy and geochemistry of the materials at Gusev to support the hypothesis that the surface materials being sampled were deposited in a lacustrine or evaporite environment. The data are consistent with materials formed by volcanic processes similar to those found throughout much of the equatorial and mid-latitudes, and locally redistributed by impact and aeolian processes.
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