MAPPING THE PIUTE MOUNTAINS, CALIFORNIA, WITH THERMAL INFRARED MULTISPECTRAL SCANNER (TIMS) IMAGES

Thermal infrared multispectral scanner (TIMS) data were acquired in 19 90 over the Piute Mountains, California, to evaluate their usefulness for lithologic mapping in an area of metamorphosed, structurally compl ex, igneous and sedimentary rocks. The data were calibrated and atmosp herically corrected, and emissivity variations in the form of alpha re siduals were extracted from which color composite images were made. Th ere was an excellent visual correlation between the units revealed in the color composite image and the lithologic units mapped in the easte rn side of the area. It was also possible to correct, improve, and ext end the recent map. For example, several areas mapped as granodioritic gneiss had TIMS alpha residual spectra consistent with mafic rocks an d were subsequently mapped as amphibolite. The presence of a swarm of mafic dikes, of which only a few had previously been identified, was a lso revealed. The images also showed color variations in granitoid plu tons that correlated with compositional variations previously determin ed by extensive field and geochemical work, The western Piute Mountain s is an area that has proven to be especially difficult to map with fi eld and air photographic methods, due to heterogeneous nature of certa in units and various levels of desert varnish. The images permitted th e extremely heterogeneous Proterozoic schists, gneisses, and granites to be easily mapped because the small-scale compositional variability was averaged to the TIMS pixel size (12 m x 12 m square). Areal measur ements from the images show that the Proterozoic rocks in the Piute Mo untains consist of granitoids (approximately 50%), biotite gneiss (app roximately 15%), pelitic gneiss (approximately 15%), quartzite (approx imately 10%), and amphibolite (approximately 10%). TIMS data can drama tically increase the efficiency and the quality of geologic mapping in well-exposed heterogeneous areas with minimal vegetation cover where detailed mapping of lithologic contacts by traditional methods is unus ually difficult.