HR: 10:50h
AN: T12D-03    [Abstracts]
TI: Recent Evolution of the Central Longmen Shan (Eastern Tibet) documented by denudation processes
AU: * Godard, V
EM: Vincent.Godard@ens-lyon.fr
AF: CEREGE, Europôle Méditerranéen de l'Arbois, Aix en Provence, 13545, France
AU: Cattin, R
AF: ENS Paris, 24 rue Lhomond, Paris, 75005, France
AU: Lavé, J
AF: CRPG, 15 rue Notre Dame des Pauvres, Vandoeuvre les Nancy, 54501, France
AU: Pik, R
AF: CRPG, 15 rue Notre Dame des Pauvres, Vandoeuvre les Nancy, 54501, France
AU: Carcaillet, J
AF: LGCA, 1381 rue de la Piscine, Saint-Martin d'Heres, 38400, France
AU: de Sigoyer, J
AF: ENS Paris, 24 rue Lhomond, Paris, 75005, France
AU: Pubellier, M
AF: ENS Paris, 24 rue Lhomond, Paris, 75005, France
AU: Bourlès, D
AF: CEREGE, Europôle Méditerranéen de l'Arbois, Aix en Provence, 13545, France
AB: Located west of the Sichuan Basin, the Longmen Shan range constitutes the eastern border of the Tibetan Plateau. It presents a steep regional topographic gradient, comparable with what is observed in the Himalayas. Nevertheless, despite this important topographic step, no significant active convergence can be detected across that border of the Plateau.
Based on those observations several authors have proposed alternative explanations for topography building and sustainment in this area. The most widely advocated model propose the existence of crustal channel flow of low viscosity material from the Plateau interior toward the Sichuan Basin (e.g. Clark et al, [2005]). This flow is supposed to be deviated by the cold rigid Yangtze Craton under the Sichuan Basin, which induces surface uplift in the Longmen Shan and would explain the existence of high topography in this area.
We present a new set of data combining (U-Th)/He thermochronometry, CRN measurements in alluvial sands, and quantitative geomorphology. Our data indicate that, (1) maximum denudation is not coincident with the high topographic front, but is located behind this area, and (2) the intensity of erosion decreases with time. From those observations we propose that the temporal and spatial evolution of denudation processes for the last 10 Myr can be associated with the propagation of a regressive erosion wave on a tectonically passive inherited topography, and that channel flow is not necessarily a prevailing mechanism for the evolution of this region.
The global implications of this scenario are evaluated using finite element thermo-mechanical modelling. We test the response to erosional unloading of a topographic step, without tectonic forcing. the output of those modellings are consistent with available data (heat flow, geodetic velocities, erosion pattern), and it appears that the action of erosion on the Plateau margin induces large scale deformation, inside the Tibetan crust.
DE: 8110 Continental tectonics: general (0905)
DE: 8159 Rheology: crust and lithosphere (8031)
DE: 8175 Tectonics and landscape evolution
DE: 9320 Asia
SC: Tectonophysics [T]
MN: 2007 Fall Meeting