Compositional variations revealed by ASTER image analysis of the Viedma Volcano, southern Andes Volcanic Zone.

Abstract

We conducted a lithological mapping of the Viedma volcano, one of five volcanoes in the Andean Austral Volcanic Zone (AVZ), using remote sensing techniques. We used data of the Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) sensor which is highly effective in geological research, to understand build-up processes and to deduce compositional variation of the Viedma volcano emerging from the South Patagonian ice field. The volcanic edifice was divided into bright parts that mainly compose the eastern flank of the volcano and dark parts at the central crater area based on the observation in visible and near infrared ranges. The SiO2 concentration was calculated using the bands in the visible and thermal infrared regions. The dark part and the bright part have approximately 51 wt% and 63 wt% average SiO2 content respectively, indicating that the exposures of the Viedma volcano have a wide variation in SiO2 concentration. Although, according to other authors, ejecta from the Viedma volcano have 64-66 wt% SiO2 and other AVZ volcanoes are essentially monolithologic dacite/andesite volcanoes, the edifice of the Viedma volcano appears to be composed mostly of basalts or older rocks/basement with low silica contents.