HR: 1340h
AN: T23C-1540    [Abstracts]
TI: Spatial and Temporal Evolution of Erosion in the Bhutanese Himalaya. What can we Learn by Combining Several Proxies?
AU: * Coutand, I
EM: icoutand@stanford.edu
AF: Universite de Lille 1, UMR-CNRS 8110 Processus et Bilan des Domaines Sedimentaires Cite scientifique Batiment SN5, Villeneuve d'Ascq, 59655, France
AU: Bookhagen, B
AF: Stanford University, Geological and Environmental Sciences Braun Hall 118, Stanford, CA 94305, United States
AU: Bernet, M
AF: Universite Joseph Fourier Observatoire des Sciences de l'Univers de Grenoble, BP53, Grenoble, 38400, France
AU: Grujic, D
AF: Dalhousie University, Department of Earth Sciences, Halifax, NS B3H 4J1, Canada
AU: Garzanti, E
AF: Universita' di Milano-Bicocca, Dipartimento di Scienze Geologiche e Geotecnologie Piazza della Scienza 4, Milano, 20126, Italy
AU: Ghalley, S K
AF: Department of Geology and Mines of Bhutan, Ministry of Trade and Industry, Thimphu, 000, Bhutan
AB: Surface erosion in the Himalaya is mostly controlled by rainfall during the Indian Summer Monsoon (ISM) season. While the ISM is a complex atmospheric phenomenon, rainfall in the Himalaya is controlled by orographic barriers with a 10-fold south to north gradient. The Kingdom of Bhutan in the eastern Himalaya is characterized by different distributions of topographic barriers that result in varying rainfall patterns. Furthermore, the Shillong Plateau ~250 km to the south of the Himalayan front imposes a significant moisture barrier for rainfall reaching eastern Bhutan. In order to investigate the different spatial distribution of erosion, we have undertaken an extensive study of 16 modern river sands collected during autumn 2004 in sandbars of the main streams. We adopted a multi chronometer approach involving cosmogenic nuclides dating, detrital apatite and zircon fission track analyzes combined with petrographic and mineralogical data in order to: 1) assess the fidelity of the detrital signal by directly comparing detrital apatite and zircon fission-track grain age distributions from a river sample collected at the outlet of a spatially restricted test catchment (Singhe Dzong valley, NE Bhutan) to modern bedrock cooling ages obtained across this catchment, 2) examine downstream development of detrital cooling ages with the changing contributing areas along the Kuri- and Koma Chhu, Mo- Po- and Puna Tsang Chhu and Thimphu- Paro- and Wang Chhu river systems (eastern, central and western Bhutan, respectively), 3) quantify the spatial distribution of erosion in the different catchments drained by these major rivers using multiple geochronometers and methods characteristic for surface processes acting at different timescales. Ultimately, our large dataset will be appropriate to test different existing models predicting the distribution, in modern landscapes, of bedrock cooling and cosmogenic nuclides ages from modern sands.
DE: 1140 Thermochronology
DE: 8175 Tectonics and landscape evolution
DE: 9320 Asia
SC: Tectonophysics [T]
MN: 2007 Fall Meeting