MULTISPECTRAL THERMAL INFRARED ANALYSIS OF MAFIC VOLCANIC ROCKS NEAR GILA BEND, ARIZONA

Mapping the variability of rocks on the surface of Mars provides one means of studying the geologic history of the planet. The igneous rock types identified on Mars using the Thermal Emission Spectrometer (TES) include basaltic to andesitic compositions. These rock types are distinguishable in the thermal infrared using spectral resolutions afforded by spectrometers such as TES, but they have not been well characterized using multispectral instruments such as the Thermal Emission Imaging System (THEMIS). The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Thermal Infrared Multispectral Scanner (TIMS) offer an opportunity to study terrestrial mafic rock compositions with multispectral instruments where there is the opportunity to compare results to field based studies and laboratory analysis of collected samples. Both the TIMS and ASTER instruments have coarser spectral resolution than THEMIS. TIMS provides 6 bands and ASTER provides 5, in contrast to the 9 unique bands for THEMIS. However, if these rock types are distinguishable at lower spectral resolutions in field conditions on Earth, THEMIS is likely to exceed their abilities at Mars.

Basaltic to dacitic rock units ranging in age from Tertiary (~20 Ma) to Quaternary (3 Ma) in the Painted Rocks Mountains of southwestern Arizona are analyzed using ASTER and TIMS remote sensing data. The multispectral remote sensing data are deconvolved using laboratory mineral and rock spectra resampled to the ASTER and TIMS instrument spectral resolutions. Comparison to laboratory and portable spectrometer data, as well as thin section analysis, provides the means to determine the accuracy of the deconvolution method. Since these rocks differ in age, they exhibit variable amounts of weathering and rock varnish. These variable properties can be used to determine the proportion of the spectral signature that is due to coatings and weathering rinds versus host rock composition.