HR: 1340h
AN: T23D-1650    [Abstracts]
TI: Can we Detect Recent Activation of the Main Central Thrust Zone from Apatite Fission Track Data and Numerical Modelling?
AU: * Robert, X
EM: xavier.robert@ujf-grenoble.fr
AF: LGCA - Universite Joseph Fourier, BP 53, Grenoble, 38000, France
AU: van der Beek, P
EM: pvdbeek@ujf-grenoble.fr
AF: LGCA - Universite Joseph Fourier, BP 53, Grenoble, 38000, France
AU: Braun, J
EM: Jean.Braun@univ-rennes1.fr
AF: Geosciences Rennes, Universite de Rennes1 Batiment 15 Campus de Beaulieu CS 74205, Rennes, 35042, France
AU: Mugnier, J
EM: Jean-Louis.Mugnier@univ-savoie.fr
AF: LGCA - Universite Joseph Fourier, BP 53, Grenoble, 38000, France
AU: Muceku, B
EM: Bardhyl.Muceku@ujf-grenoble.fr
AF: LGCA - Universite Joseph Fourier, BP 53, Grenoble, 38000, France
AB: We study the recent dynamics of the Himalayan orogen in central Nepal with the specific goal of quantifying the onset of activity and the deformation history recorded by the different major thrusts. Here, we focus on the possible reactivation of the footwall of the MCT, which is marked by a strong topographic transition in the Nepal Himalaya. This transition is too sharp to be interpreted as a simple consequence of erosion and tectonic mechanisms, such as out of sequence thrusting (Hodges et al., 2004) or underplating over a major crustal ramp (Bollinger et al., 2006) have been suggested. We report 14 new apatite fission-track (AFT) ages collected along a north - south transect from Langtang in the High Himalaya to the Terai Plain. AFT ages are consistently young (< 3 My) all along the N-S transect in the MCT zone and older (4 to 6 My) in the southern part of the Lesser Himalaya. The topographic transition does not correspond to a sharp AFT age transition. We perform numerical thermal-kinematic modelling, using a modified version of the PECUBE code (e.g. Braun, 2002), to quantify the respective roles of underplating and out-of-sequence thrusting in the shortening of this part of the Himalayan range. In these initial models, we assume steady state between tectonic accretion and surface erosion. The current dataset cannot discriminate the two models: although out-of-sequence thrusting and reactivation of the MCT shear zone are consistent with the data, they do not require such a mechanism. The presence of a crustal ramp below the topographic transition exerts the primary control on age patterns. Therefore, the question of possible out-of-sequence reactivation appears secondary in face of the current data set.
DE: 1140 Thermochronology
DE: 8038 Regional crustal structure
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: 2007 Fall Meeting