HR: 1340h
AN: T23C-0569 [Abstracts]
TI: Fluvial Incision and Exhumation Along the Eastern Margin of the
Tibetan Plateau
AU: * Godard, V
EM: godard@geologie.ens.fr
AF: Laboratoire de Géologie, Ecole Normale Supérieure, 24, rue Lhomond, Paris, 75005
France
AU: Lavé, J
EM: jlave@ujf-grenoble.fr
AF: Laboratoire de Géologie des Chaînes Alpines, CNRS, 1381, rue de la Piscine, Saint Martin d'Heres,
38400
France
AU: Cattin, R
EM: cattin@geologie.ens.fr
AF: Laboratoire de Géologie, Ecole Normale Supérieure, 24, rue Lhomond, Paris, 75005
France
AU: de Sigoyer, J
EM: sigoyer@geologie.ens.fr
AF: Laboratoire de Géologie, Ecole Normale Supérieure, 24, rue Lhomond, Paris, 75005
France
AU: Pubellier, M
EM: manupub@geologie.ens.fr
AF: Laboratoire de Géologie, Ecole Normale Supérieure, 24, rue Lhomond, Paris, 75005
France
AU: Pik, R
EM: rpik@crpg.cnrs-nancy.fr
AF: Centre de Recherche Pétrographiques et Géochimiques, CNRS, 15, rue Notre Dame des Pauvres, Nancy,
54501
France
AU: Zhu, L
EM: zld@cdut.edu.cn
AF: Chengdu University of Technology, Erxlanqiao Donglu 3, Chengdu, 610000
China
AB:
The Longmen Shan Belt along the eastern edge of the Tibetan Plateau, marks a sharp topographic transition between the low
elevated Sichuan Basin and the Plateau (~ 3500 m gain of
elevation in 75 km of horizontal distance).
Despite this high topographic gradient, no significant quaternary deformation has been inferred from available geodetic or
geomorphic data. As the Longmen Shan are a place of active erosion driven by fluvial incision and massive landslides, this
raises the question of how this topographic scarp is maintained and evolves at geological
time scales.
We've quantified fluvial incision by the survey of incised
fluvial strath terraces along the rivers draining the frontal part of the range. Surveyed Late Pleistocene terraces have
generally been uplifted by 20 to 100 meters and seem to attest for frontal fold and fault activity here. Starting from those
local incision rates we calibrate an erodibility coefficient of a detachment limited incision law [Lavé and Avouac, 2001],
accounting for climatic/lithologic/sediments local conditions, and then derive continuous incision rate profiles along these
rivers. Our preliminary results suggest that the incision in the frontal part of the Longmen Shan is in the 1-2
mm.yr-1 range, with a sligth increase in the vicinity of the Penguan massif.
In addition we present new thermochonological data ((U-Th)/He in zircons) in order to obtain a more detailed picture of the
exhumation pattern in our area of interest. Our first results suggest that the exhumation history of the Longmen Shan
displays a transition at ~ 8 Myr between a period of subdued denudation (< 0.1 mm.yr-1) and a
period characterized by higher (0.5-1 mm.yr-1) exhumation rates until today, as observed from the Late
Pleistocene fluvial terraces. This exhumation increase might correspond to some uplifting of the Plateau in this area at the
end of the middle Miocene.
DE: 1815 Erosion
DE: 8107 Continental neotectonics (8002)
DE: 8175 Tectonics and landscape evolution
DE: 9320 Asia
DE: 9604 Cenozoic
SC: Tectonophysics [T]
MN: Fall Meeting 2005