HR: 1340h
AN: T23D-1643    [Abstracts]
TI: Slow steady exhumation of the high elevation Deosai Plateau (Northern Pakistan Himalaya) since 40 Ma
AU: * Van Melle, J
EM: jeremie.van-melle@ujf-grenoble.fr
AF: LGCA, Universite Joseph Fourier, BP 53, Grenoble, 38400, France
AU: van der Beek, P
EM: pvdbeek@ujf-grenoble.fr
AF: LGCA, Universite Joseph Fourier, BP 53, Grenoble, 38400, France
AU: Guillot, S
EM: sguillot@ujf-grenoble.fr
AF: LGCA, Universite Joseph Fourier, BP 53, Grenoble, 38400, France
AU: Pecher, A
EM: Arnaud.Pecher@ujf-grenoble.fr
AF: LGCA, Universite Joseph Fourier, BP 53, Grenoble, 38400, France
AU: Latif, M
EM: gspisd@yahoo.com
AF: Geological Survey of Pakistan, Plot 84, Street 3, Islamabad, H-8/1, Pakistan
AB: Mountain ranges of the north-western Himalaya in Pakistan show strongly contrasting relief, opposing steep, deeply incised topography with extremely high peaks such as the Karakorum Range and Nanga Parbat Haramosh Massif (NPHM), to high-altitude, low-relief areas such as the Deosai Plateau located between the Karakorum and NPHM and the Tso-Morari Massif in Eastern Ladakh. In contrast, mean elevations of the different mountain ranges are comparable, the Deosai Plateau being on average even slightly higher than the adjacent NPHM. The aim of this study is to quantify the exhumation history the Deosai Plateau, in order to understand how to build such a high-altitude, low-relief plateau and how to preserve it over million-year timescales. Here, we report the first low-temperature thermochronologic data from the Deosai Plateau, to compare its exhumation history to that of the surrounding massifs. Apatite Fission Track (AFT) ages reported in the literature from the NPHM and Karakorum are extremely young (<1 Ma for the NPHM and between <1 and 7 Ma in Karakorum) implying exhumation rates >1 km/Ma. In contrast, our AFT ages from the Deosai Plateau are 15-27 Ma; an order of magnitude older than those of the surrounding massifs. Zircon and apatite (U-Th)/He ages (measured at U of Arizona, HeDWaAZ program) range from 23-45 Ma, and 12-15 Ma, respectively. Modeling the combined AFT and He ages requires continuous and very slow long term cooling rates (around 4 ° C/Ma), consistent with an exhumation rate of about 0.15 km/Ma for typical geothermal gradients. Our data thus suggest steady slow unroofing of the Deosai Plateau since at least 40 Ma. A clear link between cooling age patterns and the geomorphology is also evident, with strongly incised, high-relief massifs showing exhumation at rates an order of magnitude faster than the low-relief plateau. AFT and ZFT ages similar to our data have been reported from the Tso Morari massif further east, characterised by similar high-elevation low-relief morphology. These morphologic zones cross the Indus and Shyok Suture zones and are apparently independent of these structures. We suggest that these isolated plateau remnants can be considered as pieces of an early, highly elevated south Tibet Plateau that were isolated from it by more recent Karakorum fault movement and associated exhumation.
DE: 1140 Thermochronology
DE: 1824 Geomorphology: general (1625)
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: 2007 Fall Meeting