Investigation of Syncollisional Extension and Basin Development in the High Himalaya (NSF EAR-0438115; 01/01/05-12/31/07; DeCelles, Kapp & Quade; Michael Murphy, U. Houston)

Although synorogenic extension has been recognized in the hinterlands of many convergent orogens worldwide (e.g. Dewey, 1988), its dynamic cause, kinematic role in orogenic development, and potential influence on thrust-belt architecture and evolution are currently being debated. Two unresolved issues regarding extension in the Himalayan thrust belt are: 1) geodynamic significance of arc-parallel extension, and 2) the persistence of arc-normal extension facilitating crustal channel flow since the Early Miocene. Although these two issues are often addressed independently, the temporal persistence of the second challenges mechanisms proposed to drive the first. Inherent in all models that describe syncollisional extension are predictions about the timing and nature of contraction, extension, basin subsidence, and paleoelevation. Remarkably, almost no data from extensional basins in the high Himalaya and their bounding faults have been collected to address such hypotheses. In this proposal we identify a region in the western Himalaya that provides a rare opportunity to address the relationships between contraction, extension, basin evolution, and paleoelevation. The Zada basin is the largest late Tertiary basin in the Himalaya and is broadly constrained to be Late Miocene to Pleistocene in age. The basin fill and its underlying basement are spectacularly exposed owing to incision by the Sutlej River, a major southward-flowing trans-Himalayan drainage. The basin currently lies at ~3500 m elevation in the hinterland of the Himalayan thrust belt and developed on top of a regionally extensive Early to Middle Miocene thrust system. The thrust system flanks a second major basin, the Kailas basin, which is considered to have developed during mid-Tertiary time, but remains poorly dated. Together, the Zada and Kailas basins archive the transition of this region from extreme elevation (>5 km) to a topographic low capable of accumulating and storing a thick succession of sediments in only a few million years. We have designed an international collaborative study that brings together scientists to study the sedimentology and paleoaltimetry of the basin fills, and the structural geology, thermobarometry, and thermochronology of flanking areas. The resulting data will provide tests of models for Himalayan orogenesis and syncollisional extension.