INTERPRETATION OF ASTER REMOTE SENSING DATA ON NORTHWEST KOHISTAN TERRANE, PAKISTANI HIMALAYAS

Remote sensing data obtained by ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) have been evaluated for lithological and structural interpretations in northwestern Kohistan terrane of the Pakistani Himalayas. Comparisons were made between inferences made from ASTER images and TM images acquired over the same area and during the same season. In the study area, three terranes are juxtaposed: the Kohistan terrane, the Karakoram terrane, and the Hindukush terrane and a compositionally diverse suite of rock units are exposed. These include clastic, carbonate and low grade metamorphic rocks of the Hindukush terrane, Karakoram Batholith, paragneiss, Triassic limestone and the young clastic sediments of the Purit Formation of the Karakoram terrane, arc volcanic and plutonic rocks of the Kohistan terrane and rocks of the Shyok Suture melange. The selected scenes were acquired in the summer season (July/August 2000) to minimize spectral interference from snow and clouds. Vegetative cover is minimal except in the valleys. The first three of the ASTER bands have a higher spatial resolution (15 m) than the Landsat TM (30 m) images and thus provide detailed topographical and geological information. The locations of the suture zones between the Kohistan terrnane, the Karakoram plate, and the Hindukush terrane are readily discernable on the ASTER data but not as well on the Landsat TM images. Similarly, faults (e.g., Reshun Fault) are also visible in ASTER data. The relatively large number of bands (14) and the longer wavelength regions (VIR 0.520-0.860, SWIR 1.600-2.430 and TIR 8.125-11.650 micrometer) covered by the ASTER data allows discrimination between a wide range of compositions that are not readily recognized from the TM data. These include carbonate, and adjoining sedimentary units, mafic and ultramafic rocks of Shyok Suture mélange, the dioritic batholiths in Kohistan and Karakoram, and the volcanic rocks of the Kohistan terrane. The latter are mafic to intermediate in compositions. ASTER data was found to be useful for lithologic and structural investigations of this highly remote and inaccessible area of northern Pakistan. Implications for similar applications elsewhere are clear.