HR: 0800h
AN: P21A-0228    [Abstracts]
TI: Effects of Chemical Weathering on TIR-Derived Bulk Compositions From Deconvolution Models of Mineral Mixtures
AU: * Rampe, E B
EM: Liz.Rampe@asu.edu
AF: Arizona State University, School of Earth and Space Exploration, P.O. Box 871404, Tempe, AZ 85287, United States
AU: Kraft, M D
EM: mdkraft@asu.edu
AF: Arizona State University, School of Earth and Space Exploration, P.O. Box 871404, Tempe, AZ 85287, United States
AU: Sharp, T G
EM: Tom.Sharp@asu.edu
AF: Arizona State University, School of Earth and Space Exploration, P.O. Box 871404, Tempe, AZ 85287, United States
AU: Rogers, A D
EM: adrogers@notes.cc.sunysb.edu
AF: Stony Brook University, Department of Geosciences, 255 Earth and Space Sciences Building, Stony Brook, NY 11794, United States
AB: The Martian surface may be chemically altered on regional scales. Thermal infrared (TIR) spectroscopy and spectral deconvolution are commonly used to determine mineral abundances of the surface. Chemically weathered surfaces tend to be intimate mixtures of igneous minerals and fine-grained alteration products. To understand how alteration products affect deconvolution models of TIR spectra and model-derived bulk compositions, we measured TIR spectra of physical mineral mixtures, composed of an igneous component (augite, andesine, or 50-50 weight percent augite-andesine) and an alteration phase (montmorillonite clay or synthetic amorphous silica). Weathering products can cause significant differences between the actual and the modeled primary igneous mineral abundances and cause the false identification of significant amounts of volcanic glass in deconvolution models (Rampe et al., 2007). We calculated the bulk oxide compositions (Hamilton et al., 2000) from spectral model results of our physical mixtures and compared them to the actual bulk compositions of the mixtures. Previous studies have shown that bulk chemical compositions can be derived from TIR spectral model results (Hamilton et al., 2001; Wyatt et al., 2001), and bulk oxide data of the Martian surface are commonly derived from spectral models of data from the Thermal Emission Spectrometer (TES) (Hamilton et al., 2001; Hurowitz et al., 2007). In alkali-vs.-SiO₂ plots, model-derived compositions for clay- bearing mixtures were similar to the actual compositions of the mixtures; however, model-derived compositions for silica-bearing mixtures varied significantly from the actual values of the mixtures. In Al₂O₃-vs.- (CaO+Na₂O+K₂O)-vs.-(FeO+MgO) ternary plots, the model-derived compositions of clay-bearing mixtures followed trends typical of terrestrial basalt weathering, whereas the model-derived compositions for silica-bearing mixtures followed trends seen in compositional data derived from TES spectra from Mars (Hurowitz et al., 2007). Our data show that chemical weathering and precipitation of amorphous silica may account for some of the chemical variations of rocks on Mars as derived from TES spectral data.
DE: 5410 Composition (1060, 3672)
DE: 5415 Erosion and weathering
DE: 5464 Remote sensing
DE: 5470 Surface materials and properties
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting