GEOLOGIC MAPPING OF THE SIERRA SAN JOSÉ MOUNTAIN RANGE, MEXICO USING ADVANCED SPACEBORNE THERMAL EMISSION AND REFLECTION RADIOMETER (ASTER) DATA: A REMOTE SENSING TOOL TO ASSIST GEOLOGIC MAPPING IN THE FIELD

Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data was used to map the Sierra San José, a 10-km by 15-km mountain range that has not been previously geologically mapped. Located near the Mexico - United States border, the Sierra San José lies at the southern edge of the basin and range province. ASTER data consists of three 15-m, six 30-m, and five 90-m resolution bands in the 0.52 to 0.86 mm, 1.65 to 2.43 mm, and 8.13 to 11.65 mm region, respectively. Nine ASTER bands in the 0.52 to 2.43 mm region were converted from radiance to reflectance data using atmospheric removal software. The ASTER dataset extended from the study area to the American side of the border where lithologic information provided by geologic maps confirmed the reflectance data calibration.

Relative band depth absorption analysis (RBD) was used to identify pixels with strong 2.20 mm, and 2.33 mm absorption features, which indicate exposures of clay minerals, and carbonate and/or Mg-OH minerals, respectively. In addition, combination RBD images and a false color composite map of ASTER bands 3 (red), 2 (green) and 1 (blue) identified pixels that had featureless spectra with high reflectance values, typical of rocks containing high percentages of quartz and/or feldspar. Image spectra of the pixels with strong 2.20 mm, and 2.33 mm absorption features and featureless image spectrum were used as reference spectra in match filter processing. Match filter images were thresholded and combined to produce a match filter map and a false color composite image. Lithologic units were also mapped using a false color composite image of three minimum noise transformation bands.

Field studies indicate that carbonates (band 8 - 2.33 mm absorption feature), altered volcanic rocks (band 6 - 2.20 mm absorption feature), and quartzites (high reflectance values and 2.20 mm absorption feature) were mapped using ASTER data. Granites with high reflectance values and moderate 2.20 mm absorption features were also mapped using ASTER data. Altered rocks defined by a strong 2.20 mm absorption feature helped delineate several intrusive rock units. Lithologic units were not successfully mapped in heavily forested areas at the top of the mountain range. Thus, field mapping was focused on vegetated areas and lithologic units of interest defined by the ASTER images and map.