Other
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p22a..07h&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P22A-07
Other
3672 Planetary Mineralogy And Petrology (5410), 5220 Hydrothermal Systems And Weathering On Other Planets, 5460 Physical Properties Of Materials, 5464 Remote Sensing, 5470 Surface Materials And Properties
Scientific paper
Thermal Emission Imaging System (THEMIS) data in Eos Chasma have revealed spatially small areas, typically mounds or knobs, with materials having significant (>~35%) fractions of silica in one or more as-of-yet unidentified phases [1]. Silica, SiO2, occurs geologically in both crystalline (e.g., quartz) and amorphous (e.g., opal, glass) forms. The identification of associated minerals and the specific silica phase(s) observed in the thermal infrared data is critical to constraining the abundance estimate further. New results from THEMIS multispectral data show that if the silica is present as quartz or one of its polymorphs (e.g., tridymite, cristobalite, coesite), it is probably equal to or less than ~35% of the modal mineralogy. If the silica is present in an amorphous form with different spectral character, such as opal, this number could increase by several tens of percent. Cherts, which are quartz in rock form, exhibit a variety of microscopic textures (e.g., microcrystalline, fibrous, and "megaquartz") [2] and contain contaminating phases that produce variations in their spectra; we have identified several chert samples that also are candidate components and could be present at abundances of several tens of percent or greater. Primary and secondary silica phases are formed by a wide array of geologic processes, many of which include interactions with ambient or hydrothermal fluids and some of which are well-known preservers of biomarkers on Earth. Thus, silica enrichments on the Martian surface are likely to be important recorders of aqueous processes, and possibly biomarkers as well. As such, an area in Eos Chasma adjacent to silica-bearing deposits has been proposed as a landing site for NASA's 2009 Mars Science Laboratory rover [3]. The majority of silica-bearing deposits are a few hundred m2 in size, and there is a paucity of high- resolution visible images with which they can be investigated. A 3-m/pixel Mars Orbiter Camera (MOC) image of a relatively large (~3 km2) silica-bearing mound reveals that it is bright-toned with numerous boulders on the summit, and has a bright-toned debris apron (including apparently bright-toned boulders) at the base of the structure. The presence of boulders suggests that the material is not friable. At the southern end of the mound, lineaments are visible, which we tentatively interpret as the surface expression of layering. The geomorphology of these materials differs from that of the regional dark-toned materials, which include primarily basaltic, and orthopyroxene- and olivine-enriched materials, according to analyses of Thermal Emission Spectrometer (TES) data [4]. This presentation will focus on updated geomorphologic and mineralogic information from analyses of MOC and THEMIS visible images and THEMIS and TES spectral data, including an exploration of the various hypotheses for the origin of the materials. [1] Hamilton, V.E. (2005), Eos Trans. AGU, 86 (52), Fall Meet. Suppl., Abstract #P24A-08. [2] Knauth, L.P. (1994), in Chert: Physical Behavior, Geochemistry, and Materials Applications, Rev. Min., 29, 233- 258. [3] Hamilton, V.E., S.L. Cady, and P.J. Boston (2006), 1st Mars Science Laboratory Landing Site Workshop, http://marsoweb.nas.nasa.gov. [3] Hamilton, V.E., et al. (2003), Meteor. Planet. Sci., 38, 871- 885.
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