title: Erosion in southern Tibet shut down at ∼10 Ma due to enhanced rock uplift within the Himalaya.
abstract: Exhumation of the southern Tibetan plateau margin reflects interplay between surface and lithospheric dynamics within the Himalaya-Tibet orogen. We report thermochronometric data from a 1.2-km elevation transect within granitoids of the eastern Lhasa terrane, southern Tibet, which indicate rapid exhumation exceeding 1 km/Ma from 17-16 to 12-11 Ma followed by very slow exhumation to the present. We hypothesize that these changes in exhumation occurred in response to changes in the loci and rate of rock uplift and the resulting southward shift of the main topographic and drainage divides from within the Lhasa terrane to their current positions within the Himalaya. At ∼17 Ma, steep erosive drainage networks would have flowed across the Himalaya and greater amounts of moisture would have advected into the Lhasa terrane to drive large-scale erosional exhumation. As convergence thickened and widened the Himalaya, the orographic barrier to precipitation in southern Tibet terrane would have strengthened. Previously documented midcrustal duplexing around 10 Ma generated a zone of high rock uplift within the Himalaya. We use numerical simulations as a conceptual tool to highlight how a zone of high rock uplift could have defeated transverse drainage networks, resulting in substantial drainage reorganization. When combined with a strengthening orographic barrier to precipitation, this drainage reorganization would have driven the sharp reduction in exhumation rate we observe in southern Tibet.
authors.affiliation: Department of Earth and Planetary Science, University of California, Berkeley, CA 94720; Berkeley Geochronology Center, Berkeley, CA 94709; mtremblay@berkeley.edu tmark.harrison@gmail.com.
authors.forename: Marissa M
authors.initials: MM
authors.lastname: Tremblay
authors.affiliation: Department of Earth and Planetary Science, University of California, Berkeley, CA 94720; Berkeley Geochronology Center, Berkeley, CA 94709;
authors.forename: Matthew
authors.initials: M
authors.lastname: Fox
authors.affiliation: Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, PA 18015;
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Schmidt
authors.affiliation: Department of Earth and Planetary Science, University of California, Berkeley, CA 94720; Berkeley Geochronology Center, Berkeley, CA 94709;
authors.forename: Alka
authors.initials: A
authors.lastname: Tripathy-Lang
authors.affiliation: Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA 90095.
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Wielicki
authors.affiliation: Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA 90095 mtremblay@berkeley.edu tmark.harrison@gmail.com.
authors.forename: T Mark
authors.initials: TM
authors.lastname: Harrison
authors.affiliation: Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, PA 18015;
authors.forename: Peter K
authors.initials: PK
authors.lastname: Zeitler
authors.affiliation: Department of Earth and Planetary Science, University of California, Berkeley, CA 94720; Berkeley Geochronology Center, Berkeley, CA 94709;
authors.forename: David L
authors.initials: DL
authors.lastname: Shuster
keywords: Tibet–Himalaya; landscape evolution; thermochronometry