Mineral Abundances in Weathered Rocks from the South Mountains of Arizona using Thermal Infrared Emission Spectroscopy and Spectral Mixture Analysis
Abstract
Thermal infrared emission spectroscopy has been extensively used for studying the mineralogical make up of rocks. Minerals have characteristic vibrational modes that give rise to diagnostic absorption features in their infrared spectra. It is important to study rocks on Earth by thermal infrared emission spectroscopy in order to better understand the results obtained by remote sensing infrared spectroscopy studies of other planetary surfaces (Michalski et al., 2004, JGR 109).
This study presents thermal infrared emission spectra of naturally weathered rocks collected from the Telegraph Pass and Dobbin's Lookout areas of the South Mountains in Arizona (Reynolds 1985, Arizona Geological Survey Bulletin 195). These spectra are analyzed using spectral mixture analysis (SMA) where the spectra are subjected to linear spectral deconvolution and the results are compared with an infrared spectral library of end member minerals to yield mineral abundances in the rock sample (Ramsey et al., 1998, JGR 103). Infrared emission spectra of a suite of 30 rock samples were recorded in the 400 cm -1 to 2000 cm -1 wavelength range with Nicolet Nexus 670 and Nicolet iS50 spectrometers located in the Mars Space Flight Facility at Arizona State University (Ruff et al., 1997, JGR 102). The infrared spectra are plotted as emissivity vs wavelength (in cm -1 ). The spectra show strong, diagnostic absorption features in the range of 1000 cm -1 to 1250 cm -1 corresponding to Si-O stretching modes and 350 cm -1 to 800 cm -1 corresponding to Si-O-Si bending modes. The Christiansen frequencies range from 1275 cm -1 to 1365 cm -1 . Spectral mixture analysis on the spectra was performed using different spectral libraries of minerals (Christensen, et al., 2000, JGR 105). The most abundant mineral groups contained in this suite of South Mountain rocks are quartz, plagioclase feldspar, and alkali feldspar. They contain 5-85% quartz, 0-35% plagioclase feldspar, and 0-35% alkali feldspar. Other minerals present, as identified by SMA, include clays, iron oxide, phosphates, and carbonates. Some weathered samples contain 30-50% clay and samples coated with desert varnish contain 40-50% iron oxide. We compare the mineral abundances obtained from SMA using the ASU general and igneous spectral libraries and a custom library of preselected end member minerals.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMEP0360016A
- Keywords:
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- 1813 Eco-hydrology;
- HYDROLOGY;
- 1824 Geomorphology: general;
- HYDROLOGY;
- 1825 Geomorphology: fluvial;
- HYDROLOGY;
- 1826 Geomorphology: hillslope;
- HYDROLOGY