HR: 0800h
AN: P21C-0165    [Abstracts]
TI: Constraints on the Global-scale Chemical Weathering State of Mars From TES Results Based on Spectral Analysis of Chemically Weathered Basalts
AU: * Michalski, J R
EM: michalski@asu.edu
AF: Arizona State University, Dept. of Geological Sciences Box 871404, Tempe, AZ 85287-1404 United States
AU: Kraft, M D
EM: mdkraft@asu.edu
AF: Arizona State University, Dept. of Geological Sciences Box 871404, Tempe, AZ 85287-1404 United States
AU: Sharp, T G
EM: tsharp@asu.edu
AF: Arizona State University, Dept. of Geological Sciences Box 871404, Tempe, AZ 85287-1404 United States
AU: Christensen, P R
EM: phil.christensen@asu.edu
AF: Arizona State University, Dept. of Geological Sciences Box 871404, Tempe, AZ 85287-1404 United States
AB: On Earth, subaerially exposed basaltic rocks (from arid-to-tropical regions) develop weathering rinds and rock coatings that affect spectroscopic measurements of their natural surfaces. Similarly, basaltic rocks and basaltic soil particles on Mars may have rinds and coatings that are spectroscopically observable. Thermal emission spectroscopy, because it provides information about the composition and structure of silicate and non-silicate minerals and mineraloids, provides a useful perspective on the mineralogy of weathered surfaces; reconciliation of the emission spectral features of weathered surfaces with observations from other datasets is critical to interpretations of thermal emission spectral features of Mars. In this study, we investigate the thermal emission (6-25 μm) and visible/near-infrared (VNIR) (0.4-2.5 μm) spectroscopic features of fresh and weathered surfaces of rock samples from the Columbia River Basalt Group (CRBG). VNIR spectra of weathered rock surfaces are brighter and redder than fresh rock surfaces, but contain no evidence for neoformation of clay minerals within subaerially exposed, weathered surfaces. In contrast, thermal emission spectroscopy suggests an enrichment of clay minerals in weathered surfaces. Also, thermal emission spectroscopy indicates the presence of glass-like materials in many weathered surfaces, which likely correspond to amorphous weathering products present within fractures, as coatings on minerals, or as coatings on the rocks themselves. These results have important implications for interpretation of TES and THEMIS data of Mars, including: 1) glasses and clays detected on Mars from thermal infrared spectra may correspond to poorly crystalline weathering products within chemically weathered rock surfaces, 2) chemically weathered surfaces of basalts may appear oxidized but clay-poor to VNIR datasets, and 3) the differential chemical breakdown of primary phases can affect interpretations of the remaining primary rock mineralogy from thermal infrared data; weathering serves to bias igneous interpretations toward rocks of higher silica and alkali contents. Trends observed in the spectral analysis of chemically weathered CRBG rock surfaces could explain some of the spectral trends observed at Mars, suggesting that martian dark region basalts have been chemically weathered under consistently low-water, or only episodically wet surface conditions.
DE: 5410 Composition (1060, 3672)
DE: 5464 Remote sensing
SC: Planetary Sciences [P]
MN: Fall Meeting 2005