See more from this Division: Topical Sessions
See more from this Session: Modes of Lithospheric Extension: Oceanic and Continental Core Complexes
Sunday, 5 October 2008: 11:00 AM
George R. Brown Convention Center, 332CF
Abstract:
The Himalayan orogen can be roughly divided into regions of crustal extension within the Tibetan Plateau and crustal shortening across the range front. In between lies a transition zone where exhumation rates are high and the potential relationships between tectonically- and climatically-driven processes can be tested. In the Mount Everest area, the east-west striking South Tibetan detachment system accommodated south-directed mid-crustal flow until the middle Miocene. Since then, deformation has been partitioned into north-south striking extensional faults and shear zones. The trans-Himalayan Ama Drime Massif (ADM) is bounded by oppositely dipping normal-sense shear zones that are kinematically linked to brittle faults that offset Quaternary deposits. Consistency in shear sense indicators in rocks that deformed at a range in temperatures suggest that normal-sense displacement was maintained during exhumation. U(-Th-)Pb geochronology conducted on rocks within the core of the ADM demonstrate that they reached granulite facies at ~12 Ma. Geochemical data from hot springs along the western shear zone indicate devolatilization of crustal rocks and potentially active metamorphism and/or melting beneath the ADM. The ADM coincides with the Xainza-Dinggye rifts system that extends into the Tibetan Plateau. Previous geomorphological investigations defined the Arun River gorge, located within the southern end of the ADM, as a candidate for climate-tectonic coupling. New (U-Th)/He apatite ages from the footwall block of the ADM yield a minimum exhumation rate of ~1 mm/yr between ~1.5 and 3.0 Ma. We propose that the deep crustal level exposed within the ADM was exhumed during orogen-parallel extension along the southern margin of the Tibetan Plateau. Focused surface denudation in the Arun River gorge interacted with tectonically-driven extension resulting in enhanced exhumation rates. These data begin to quantify the timing of mid-crustal flow and exhumation and provide insights into the dynamic interactions between climate and tectonic processes during orogen-parallel extension.
See more from this Division: Topical Sessions
See more from this Session: Modes of Lithospheric Extension: Oceanic and Continental Core Complexes