HR: 0800h
AN: T41A-1279    [Abstracts]
TI: Extreme Exhumation Within the Sichuan Basin - Late Cenozoic Erosion, Sedimentation and Tectonics at the Eastern Margin of the Tibetan Plateau Based on Apatite Fission Track Thermochronology.
AU: * RICHARDSON, N
EM: nick@erdw.ethz.ch
AF: ETH Zurich (Swiss Federal Institute of Technology), Geological Institute, Department of Earth Sciences, Sonneggstrasse 5, ETH Zentrum, Zurich, CH-8092 Switzerland
AU: Densmore, A L
EM: alexander.densmore@erdw.ethz.ch
AF: ETH Zurich (Swiss Federal Institute of Technology), Geological Institute, Department of Earth Sciences, Sonneggstrasse 5, ETH Zentrum, Zurich, CH-8092 Switzerland
AU: Seward, D
EM: diane.seward@erdw.ethz.ch
AF: ETH Zurich (Swiss Federal Institute of Technology), Geological Institute, Department of Earth Sciences, Sonneggstrasse 5, ETH Zentrum, Zurich, CH-8092 Switzerland
AU: Yong, L
EM: liy@cdut.edu.cn
AF: Chengdu University of Technology, National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Sichuan, Chengdu, 610059 China
AB: The Tibetan Plateau represents the most impressive geomorphic expression of the effects of continental collision on the Earth's surface. Despite being the focus of much research over the last decades, there are still numerous outstanding questions regarding the mechanisms and timing of plateau formation, and regional lithospheric structure. The eastern margin of the plateau is a particularly key location for the assessment of these issues. This margin, commonly referred to as the Longmenshan, presents a formidable topographic front, yet appears not to have experienced significant shortening since the Triassic, and is not accompanied by major Cenozoic thrusting and associated foreland basin deposits within the adjacent Sichuan Basin. The means by which such extreme relief is produced and maintained are therefore somewhat enigmatic. Previous studies have suggested that focused late Cenozoic exhumation took place along the eastern margin of the Tibetan Plateau, but in this study, we demonstrate that significant exhumation also took place within the adjacent Sichuan Basin. Using new apatite fission track thermochronological data and compilations of vitrinite reflectance data, we place constraints on the magnitude and timing of Cenozoic exhumation, and of post-exhumation deformation, adjacent to the eastern Tibetan Plateau. We calculate that between 2 and 4 km of sedimentary basin fill was removed during the late Tertiary across the entire Sichuan Basin. This event is marked by a widespread regional unconformity between Cretaceous to Eocene fine-grained clastic rocks and late Neogene conglomerate within the western Sichuan Basin. Determination of the location of the base of the apatite partial annealing zone allows us to establish exhumation patterns across the Tibetan Plateau margin and into the Sichuan Basin. Field observations, heavy minerals and clast compositional analyses of late Neogene sediments within the basin also permit us to constrain the timing of the latest deformational phase along the margin, and allow us to reconstruct major drainage pattern reorganization that has taken place between the late Neogene and Recent. Clearly, the rapid removal of such large quantities of material from the Sichuan Basin has important implications for the surrounding lithosphere, and for our understanding of the tectonic and sedimentary history of this margin of the Tibetan Plateau. We close by speculating on the erosional mechanisms involved in such large-scale basin evacuation.
DE: 1140 Thermochronology
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 8110 Continental tectonics: general (0905)
DE: 8169 Sedimentary basin processes
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: Fall Meeting 2005