HR: 0800h
AN: P21A-0210    [Abstracts]
TI: Mineralogy of Natural Basalt Weathering Rinds With Application to Thermal Emission Spectra of Mars
AU: * Kraft, M D
EM: mdkraft@asu.edu
AF: Arizona State University, Department of Geological Sciences, Box 871404, Tempe, AZ 85287-1404 United States
AU: Michalski, J R
EM: michalski@asu.edu
AF: Arizona State University, Department of Geological Sciences, Box 871404, Tempe, AZ 85287-1404 United States
AU: Sharp, T G
EM: tsharp@asu.edu
AF: Arizona State University, Department of Geological Sciences, Box 871404, Tempe, AZ 85287-1404 United States
AU: Christensen, P R
EM: phil.christensen@asu.edu
AF: Arizona State University, Department of Geological Sciences, Box 871404, Tempe, AZ 85287-1404 United States
AB: Mineralogy of Natural Basalt Weathering Rinds With Application to Thermal Emission Spectra of Mars M.D. Kraft, J.R. Michalski, T.G. Sharp, (and P.R. Christensen?) Chemically weathered rocks have been suggested to cover a significant portion of the Martian surface based on orbiter observations, and rocks investigated by the Mars Exploration Rover at the Gusev landing site show evidence of chemical alteration and weathering rinds. To understand remote mineralogical and chemical measurements of altered rock surfaces, whether in situ or from orbit, it is important to understand the general characteristics of weathering rinds (e.g., secondary mineralogy and microstructure in rinds) and how these characteristics affect remote observations. We are investigating a suite of weathered rocks of the Columbia River Basalt Group (CRBG) to identify chemical, mineralogical, and micro-structural changes associated with weathering and determine how these changes influence thermal emission measurements. Preliminary work shows that thermal emission spectra of weathered surfaces can vary substantially from spectra of fresh rocks despite rather low degrees of alteration in weathered surfaces. In rocks studied thus far, the predominant difference between the unweathered rock and weathering rind is an increase in porosity in the rind due to dissolution and/or volume expansion, causing a substantial increase in the volume density of micron-scale cracks. Mineralogical differences are imparted in the rind by the (partial) infilling of cracks by secondary materials that are Si, Al, and Fe-rich. A previous investigation by Colman (1982) showed that secondary silicates in basalt weathering rinds were dominantly X-ray amorphous. High-resolution secondary electron imaging of crack-filling products reveals spheroid-shaped materials, 10s of nm in diameter, which are consistent with short-range order allophane. We are currently performing additional analyses using XRD and TEM to constrain the mineralogy of secondary phases in CRGB weathering rinds, including the crystallinity of secondary silicates. Assessing chemical weathering on Mars may rely largely on the ability to detect and constrain the mineralogy of short-range order silicates, which may be the dominant Martian weathering products. Thermal emission spectroscopic data of Mars, with the detailed understanding that we intend to provide with this study, provides a unique and excellent means of constraining the nature of silicate weathering on Mars.
DE: 5410 Composition
DE: 5415 Erosion and weathering
DE: 5464 Remote sensing
DE: 5470 Surface materials and properties
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting