Age Constraints for the Zhada Basin, SW Tibet Based on Cosmogenic Radio-Nuclides

Joel Saylor
Department of Geosciences University of Arizona Tucson, Arizona; [email protected]

The Zhada Basin is a late-Cenozoic sedimentary basin in the largely unstudied southwestern Tibetan Plateau. The basin lies between the South Tibetan detachment system to the southwest, the Indus Suture to the northeast, and the Leo Pargil and Gurla Mandhata gneiss domes to the northwest and southeast, respectively. Normal faulting on the South Tibetan detachment system likely predates 12 Ma (Murphy and Yin, 2003). Normal faulting adjacent to the gneiss domes initiated in the mid-late Miocene (Murphy et. al., 2002; Thiede et. al., 2006) and is ongoing today. The basin fill, consisting of >800 m of fluvial, lacustrine, eolian and alluvial fan deposits, is undisturbed and lies in angular unconformity above the Tethyan fold-and-thrust belt. After deposition, the basin was incised to basement by the Sutlej River.

The top surface of the basin sediments is a paleo-depositional plain. We collected surface and shielded samples for cosmogenic radio-nuclide exposure dating from this surface. We also collected magnetostratigraphic samples from two complete stratigraphic sections. Initial results of cosmogenic radio-nuclide dating indicate that the paleo-depositional plain has an age of ~50 ka. Coupled with magnetostratigraphy this indicates that basin filling occurred between 9.2 – 0.05 Ma. These results provide important constraints on 1) the transition from arc-normal compression to arc-parallel extension recorded in the Zhada Formation, 2) dating of the vertebrate and invertebrate fossils in the basin, 3) the onset of incision linked to integration of the modern Sutlej River system and 4) establishing a high-resolution climate record based on the Zhada Formation.

AAPG Search and Discovery Article #90083 © 2008 AAPG Foundation Grants in Aid