Mineralogy and Geologic Context of Bedrock Exposures in Mare Serpentis, Mars

Details Mineralogy and Geologic Context of Bedrock Exposures in Mare Serpentis, Mars Mineralogy and Geologic Context of Bedrock Exposures in Mare Serpentis, Mars

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p22a..08r&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #P22A-08

Mathematics

Logic

5410 Composition (1060, 3672), 5464 Remote Sensing, 5470 Surface Materials And Properties, 6225 Mars

Scientific paper

Numerous exposures of bedrock (defined here as surfaces that exhibit thermal inertia values > 1200 J m^{- 2}K-1s^{-1/2}) have been identified on Mars from THEMIS data [e.g., 1]. Relative to surfaces dominated by sands, these sites are likely to consist of locally-derived materials (ie, true bedrock or blocks derived from the underlying rock), with little compositional contamination from mobile surface layer materials. The ability to confidently place observed compositions in their original geographic and stratigraphic context provides insight into the mineralogic heterogeneity of the crust and degree of influence from aqueous processes on the surface. In addition, characterization of these rare sites provides a link to results from previous spectroscopic studies, most of which determined compositions on a much larger scale and were limited to measurements of somewhat mobile materials. Three exposures located in the intercrater plains of Mare Serpentis, Mars (17-25°S,45-49°E) were analyzed using MGS and Mars Odyssey datasets. The bedrock regions measure ~30-700 sq km in area and are separated by ~100-300 km. Visible images from MOC and THEMIS were used to examine the contacts between bedrock and surrounding lower inertia plains. Two of the bedrock surfaces appear to consist of a darker toned, competent unit that is superposed on the surrounding plains. The third region consists of a lighter toned unit that lies below a darker, competent unit. Although brightness differences are observed, TES albedo values vary by less than .01 between the plains and bedrock surfaces. No bedforms are observed in the available THEMIS visible images of the bedrock surfaces, consistent with the extremely high thermal inertia and indicating a dominance of blocky material. TES dust cover index values are >0.97, consistent with relatively dust-free surfaces. THEMIS multispectral images and TES spectra indicate that in general, the bedrock surfaces exhibit greater abundance of olivine and pyroxene, and lower abundance of plagioclase than the surrounding lower thermal inertia areas. However, preliminary analysis of TES spectra suggests that absolute abundances of plagioclase, orthopyroxene, clinopyroxene and/or high-silica phases may vary between the bedrock regions. Comparison of bedrock and surrounding plains spectra from individual TES orbits indicate that sulfates are modeled at abundances of 10-15% (right at the TES detection limit) for the bedrock surfaces, and well below the detection limit for the surrounding plains. Further analysis using additional techniques is needed to validate these potential differences. Finally, THEMIS infrared images show that two of the bedrock regions are superposed by a ~50 m thick, lower thermal inertia layer that exhibits higher plagioclase and total pyroxene abundance, and lower high-silica phase abundance, suggesting a similar sequence of processes/events may have occurred in both regions. A synthesis of these and additional geologic and mineralogic observations and their implications will be presented. [1] Edwards, C. S. et al., Eos Trans. AGU, 86(52), Fall Meet. Suppl., Abs. P21C-0158.

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