Mapping granite and gneiss in domes along the North Himalayan antiform with ASTER SWIR band ratios

Abstract

A series of five gneiss domes that are exposed along the axis of the North Himalayan antiform 50 km south of the Indus-Tsangpo suture, southern Tibet, are characterized by cores of Cambrian gneiss and Neoproterozoic-Paleozoic schists and migmatites, often intruded by Tertiary granites and mantled by metamorphosed equivalents of Tethyan sedimentary successions. Images from the SWIR (short wave infrared) bands recorded by the ASTER (Advanced Spaceborn Thermal Emission and Reflection Radiometer) sensor on the Earth Observation System Terra satellite reveal with unprecedented clarity the nature of the cores of the domes and the extent of the surrounding mantles of metamorphic rock. Using band ratio methods, we distinguish Tertiary granite from Cambrian gneiss on the basis of the presence of 5%–10% muscovite in the granite. This methodology is ideally suited to the mapping of a relatively inaccessible area with excellent exposure but limited ground truth. With the exception of the well-studied Kangmar dome, our images of the cores of the domes and their associated mantles bear little resemblance to the published geological maps of the region and reveal hitherto unrecognized exposures of granites. The true disposition of the domes within the North Himalayan antiform have now been established, revealing a systematic westward increase in the granite component of Himalayan age within the domes across the study area.