Chemistry and Mineralogy of the Regolith at the Gusev Plains

Details Chemistry and Mineralogy of the Regolith at the Gusev Plains Chemistry and Mineralogy of the Regolith at the Gusev Plains

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p21a0220w&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #P21A-0220

Mathematics

Logic

5400 Planetology: Solid Surface Planets, 3600 Mineralogy And Petrology (Replaces, 1000 Geochemistry (New Field, Replaces Rock Chemistry)

Scientific paper

During sols 91 to 158, the Spirit rover traveled 2.3 km across the plains between the Bonneville crater and the Columbia Hills at Gusev crater. A fast traverse was designed for this part of the mission, to save time and rover resources for further investigations once Spirit arrived at the Columbia Hills. Nevertheless, a set of systematic science observations was conducted by Spirit during this travel for the morphologic, chemical, and mineralogical characterization of the rocks and soils of the plains. In addition to near- and mid-field rock surveys, thermophysical property measurements of soils, and atmospheric observations, one set of rover track observations (Pancam multicolor images and MiniTES spectra) was carried out every fourth driving sol. Two trenches were dug by the right-front wheel of Spirit at sols 113 and 135. Subsurface regolith at different depths was exposed in the wheel tracks and trenches. The trenches were studied by the full Athena science instrument payload. Also, short integration Moessbauer and APXS measurements were made inside of two rover tracks in addition to standard Pancam and MiniTES observations. For the regolith within both trenches (Big Hole ~ 6 cm and Boroughs ~ 11 cm deep), compared with the surface analyses, the APXS data showed higher S, Mg, Cl, the Moessbauer and Pancam spectral analyses showed higher oxidation state, and the Microscopic Imager revealed differences in soil cementation. In the Boroughs trench, Fe2+ in olivine decreases with increasing Fe3+/Fetotal. A normative calculation using APXS data, along with Moessbauer curve-fitting results to constrain the Fe-oxides, suggests a 16-20 wt% of MgSO4 and a decrease in olivine, Ca-feldspar, and Ca-pyroxene proportions in the regolith comparing with the Gusev surface regolith. Our analysis suggests a relatively low degree of alteration of the rocks and regolith around the trench site in a probably acidic environment. During the alteration, olivine grains were partially dissolved; some Fe2+olivine may have converted into Fe-oxides; magnesium ions were released from olivine and transported by fluids, and eventually deposited as Mg-sulfate in the regolith of topographically low plains. The fluids involved in this alteration may have been short-lived, sporadic, and present only in small quantities. The vertical profiles of S, Mg, and Fe3+ in the regolith at the Boroughs may reflect the combination of fluid collection, evaporation, and mineral deposition.
Alteration of basaltic material by water is clearly indicated by the investigations at the plains during the travel from the Bonneville crater to the Columbia Hills. Based on the geology, mineralogy, and chemistry, we consider that the plains are distinct in character from the Bonneville crater ejecta, and from the Columbia Hills now under exploration.

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