HR: 08:30h
AN: T21E-03    [Abstracts]
TI: Miocene-Pliocene range growth and basin evolution in NE Tibet, Laji-Jishi Shan and surrounding basins.
AU: * Lease, R O
EM: rlease@crustal.ucsb.edu
AF: Department of Earth Science, University of California, Santa Barbara, CA 93106, United States
AU: Burbank, D W
EM: burbank@crustal.ucsb.edu
AF: Department of Earth Science, University of California, Santa Barbara, CA 93106, United States
AU: Zhang, H
EM: beijingzhhuiping@163.com
AF: Institute of Geology, China Earthquake Administration P.O.Box 9803, Beijing, 100029, China
AU: Farley, K A
EM: farley@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, California Institute of Technology 1200 E. California Blvd., Pasadena, CA 91125, United States
AU: Daoyang, Y
EM: yuandaoyang@163.com
AF: Institute of Geology, China Earthquake Administration P.O.Box 9803, Beijing, 100029, China
AB: The lateral expansion and upward growth of the Tibetan Plateau remains enigmatic, despite its relevance for exploring both the geodynamics responsible for the world's largest topographic perturbation and its climatic consequences. Here we apply (U-Th)/He thermochronology, detrital zircon provenance, and magnetostratigraphy to constrain the timing and nature of uplift, erosion, and deposition along a transect that crosses the plateau's NE margin in the vicinity of the Laji-Jishi Shan. The Hualong basin has a 1.5-km-thick, coarsening-upward fluviolacustrine stratigraphic succession. High-resolution magnetostratigraphy (500 sites) yields a reasonable correlation to the magnetic timescale between 2.1 Ma - ~10.7 Ma. (Notably, this section records several short- lived geomagnetic excursions.) Hualong basin experienced a striking, 2.5-fold increase in sediment accumulation after ~8.5 Ma, presumably due to accelerated exhumation of the adjacent Laji-Jishi Shan. However, this increase could also reflect erosion of the West Qinling to the south. Given the distinctive detrital zircon U/Pb age signature of sediment derived from each range, we are using the U/Pb provenance tool to determine the relative influences of the contrasting sediment sources and their evolution. This will help discern whether the sustained increase in sedimentation is primarily due to tectonic forcing (erosion of one range) or whether intensification of the monsoon is responsible for an enhanced sediment supply regionally (erosion of multiple ranges). Additionally, new (U-Th)/He ages from the Laji-Jishi Shan exhibit two clusters: one in the early Miocene and one in the late Miocene. This may reflect two episodes of rapid cooling restricted to localized portions of the range. Erosion during the late Miocene event is a likely cause of the coeval, 2.5-fold increase in sedimentation rates. Cross-sections of the region indicate <25% Cenozoic shortening.
DE: 1140 Thermochronology
DE: 1520 Magnetostratigraphy
DE: 8108 Continental tectonics: compressional
DE: 8169 Sedimentary basin processes
DE: 8177 Tectonics and climatic interactions
SC: Tectonophysics [T]
MN: 2007 Fall Meeting