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Histoire thermochronologique et variations morphologiques en Himalaya du nord-ouest

Abstract : The Himalayan orogen, with a length of close to 2500 km, is the result of the col-lision of the Indian and Eurasian continents, which initiated 55 My ago. Since the onset of collision, the morphology of the Himalaya/Tibet region has not ceased to evolve, controlled by tectonics and erosion. At its north-western extremity, the Hi-malayan belt shows strongly contrasting relief, with regions of very high relief encir-cling areas characterised by high elevation and low relief. The best example of the latter areas is without doubt the Deosai Plateau. Located at ~4000 m mean eleva-tion on Kohistan/Ladakh Arc terrains, it is surrounded by strongly incised massifs such as the Karakorum and the Nanga Parbat. These two massifs contain 6 of the 14 summits with an altitude higher than 8000 m in the world.
This study presents a morphological analysis coupled with a thermochronologi-cal study of the north-west Himalaya, based on two fieldwork campaigns on and around the Deosai Plateau. This multi-method approach allows us to: (1) precise the morphological characteristics of the north-western Himalayan region and (2) highlight the formation and exhumation history of the low-relief, high-elevation ar-eas, which have been little investigated in this context.
Morphological analyses on the scale of the entire north-west Himalaya show that several zones of low relief at high elevation exist west of the Karakorum Fault, both north and south of the Indus-Tsangpo Suture Zone. The thermochronologic study allows us to present the first low-temperature thermochronology data (AFT and (U-Th)/He on apatite and zircon) from this part of the Kohistan/Ladakh Arc. Thermal history modelling using these data and their comparison with published data, sug-gest that the low-relief, high-elevation surfaces have formed since 30-40 Ma. Since this time, these surface evolved slowly, due to very low exhumation rates (~200 m.My-1), unlike the surrounding strongly incised massifs characterised by extremely high exhumation rates (several km.My-1 for the Nanga Parbat since ~10 Ma). A mor-phological study of the rivers draining the Deosai Plateau, together with thermo-kinematic modelling of the evolution of its northern border, show that erosion is localised within the major valleys and is not very efficient within the plateau. The exhumation histories and morphological characteristics of the low-relief, high-elevation regions are very similar to those from the western Tibetan Plateau, sug-gesting that in Eocene time they formed a single block. The high-elevation, low-relief areas to the west of the Karakorum Fault were individualized by localized erosion in the main river valleys, guided by the major tectonic structures.
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Contributor : Jérémie van Melle <>
Submitted on : Monday, February 2, 2009 - 5:43:17 PM
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  • HAL Id : tel-00358121, version 1



Jérémie van Melle. Histoire thermochronologique et variations morphologiques en Himalaya du nord-ouest. Sciences de la Terre. Université Joseph-Fourier - Grenoble I, 2008. Français. ⟨tel-00358121⟩



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