Characterization of Natural Mixed-Layer Illite/Smectite and Physical Mixtures of Illite and Smectite Using TIR and VNIR Spectroscopy: Are Mixed-Layer Clays on Mars?

Details Characterization of Natural Mixed-Layer Illite/Smectite and Physical Mixtures of Illite and Smectite Using TIR and VNIR Spectroscopy: Are Mixed-Layer Clays on Mars? Characterization of Natural Mixed-Layer Illite/Smectite and Physical Mixtures of Illite and Smectite Using TIR and VNIR Spectroscopy: Are Mixed-Layer Clays on Mars?

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p53b1444r&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #P53B-1444

Other

1039 Alteration And Weathering Processes (3617), 3665 Mineral Occurrences And Deposits, 5410 Composition (1060, 3672), 5464 Remote Sensing, 5494 Instruments And Techniques

Scientific paper

Interpretations of visible/near-infrared (VNIR) spectral data from OMEGA and CRISM identify a variety of phyllosilicate minerals in Noachian terrains on Mars, including Fe/Mg smectites, montmorillonite, kaolinite, muscovite or illite, and chlorite [Bibring et al., 2005 and 2006, Poulet et al., 2006, Wray et al., 2008, Mustard et al., 2008, and Ehlmann et al., 2008]. In many areas, different phyllosilicates are found in close proximity to one another. For example, OMEGA and CRISM data from Mawrth Vallis provide evidence for the presence of extensive outcrops rich in Fe/Mg smectites and montmorillonite, while CRISM data from Nili Fossae provide evidence for the presence of limited outcrops rich in high-Fe chlorite, kaolinite, and muscovite/illite [Mustard et al., 2008]. The identification of multiple types of clay minerals in close proximity introduces the question: Could any of these outcrops contain mixed-layer clay minerals? Mixed-layer clays form as a result of chemical weathering or low-temperature hydrothermal alteration in volcanic environments or due to low-grade metamorphism [Srodon, 1999]. It is important to be able to identify mixed-layer clays through remote sensing measurements for two reasons. Evidence for hydrothermal alteration (silica-enriched deposits in Gusev crater [Squyres et al., 2008]) and chemical weathering (global iron oxidation and the enrichment of a high-silica phase in northern mid to high latitudes [Kraft et al., 2007]) suggests that mixed-layer clays are likely on Mars. Secondly, the ratios of the individual clay components formed from hydrothermal alteration can act as a geothermometer and constrain the temperature of the environment of formation [Srodon, 1999]. In this study, we compare VNIR and thermal IR spectral data from natural mixed-layer illite-smectite samples to physical mixtures of illite and smectite in similar ratios to determine how to recognize mixed-layer clays and distinguish them from mixtures of individual clays. This study will provide the basis needed to further interpret martian VNIR spectra of clay-rich regions and investigate the presence of mixed-layer clays.

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