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The Kumaun and Garwhal Lesser Himalaya, India: Part 2. Thermal and deformation histories

Célérier, Julien and Harrison, T. Mark and Beyssac, Olivier and Herman, Frédéric and Dunlap, William J. and Webb, A. Alexander G. (2009) The Kumaun and Garwhal Lesser Himalaya, India: Part 2. Thermal and deformation histories. Geological Society of America Bulletin, 121 (9-10). pp. 1281-1297. ISSN 0016-7606.

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An integrated petrologic, thermochronologic, and numerical modeling study constrains the thermal evolution of the Lesser Himalayan Sequence in the Kumaun and Garwhal regions of India. South of the Tons thrust, peak metamorphic temperatures do not exceed 330 °C. On the northern side, a transition toward higher temperatures adjacent to the Main Central thrust hanging wall is documented. In the immediate footwall of the Main Central thrust, peak temperatures average ~550 °C. An inverted thermal field gradient of ~30 °C/km beneath the Vaikrita thrust is calculated. An inverted thermal field gradient of ~20 °C/km is also documented beneath a klippe of the Main Central thrust hanging wall ~25 km south of the Vaikrita thrust, and a peak footwall temperature of 530 °C is recorded close to the shear zone at the base of the klippe. The mechanism for thermal metamorphism in the Lesser Himalayan Sequence is interpreted to be conduction of heat from the Main Central thrust fault and/or hanging wall to the footwall. A localized thermal field gradient is also associated with the Tons thrust. The ^(40)Ar/^(39)Ar thermochronology reveals that the exposed rock in the Kumaun and Garwhal Lesser Himalaya underwent cooling below the closure temperature (Tc) for white mica at different times in the late Tertiary. The proximal footwall of the Munsiari thrust experienced cooling below the white mica Tc at ca. 8.5 Ma. South of the Munsiari thrust, in the proximal footwalls of the Chaukori and Askot klippen, muscovites ages are ca. 11.5 Ma, ~3 Ma older than samples to the north. The age differences in samples from northern and southern exposures are interpreted to document cooling related to thermal relaxation following passage of the Main Central thrust hanging wall atop the Lesser Himalayan Sequence. Results of thermal modeling achieve good fits to the data when scenarios involve an early Miocene phase of overthrusting of a hot hanging wall over a downgoing footwall, followed by the initiation of a duplex within Lesser Himalayan Sequence rocks.

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Additional Information:Copyright © 2009 by Geological Society of America. RECEIVED FOR PUBLICATION October 15, 2007. REVISED MANUSCRIPT RECEIVED November 29, 2008. MANUSCRIPT ACCEPTED December 8, 2008. This version was published on September 1, 2009. We thank Kurt Stüwe, an anonymous reviewer, and Associate Editor Matt Kohn for constructive reviews. An Yin is thanked for allowing us to publish Figure 1. Discussions with Amos Aikman and Jean-Philippe Avouac were central to the development of themes presented here. Dr. Chandra Dubey and Kuldeep Chaudhary of the University of Delhi are thanked for field support. This work was supported by Australian Research Council Discovery grant DP0343646: Tectonic Reconstruction of the Evolution of the Alpine-Himalayan Orogenic Chain. Funding by Institut National des Sciences de l'Univers, Dynamique et Evolution de la Terre interne and Agence National de la Recherche, jeune chercheur GeoCarbons to Olivier Beyssac is acknowledged. GSA Data Repository item 2009074, data tables presenting results of the Raman Spectroscopy of Carbonaeous Material and ^(40)Ar/^(39)Ar dating and details of the analytical methods used to generate Geochemical data, is available at or by request to
Group:Caltech Tectonics Observatory
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Australian Research CouncilDP0343646
Institut National des Sciences de l'UniversUNSPECIFIED
Agence National de la RechercheUNSPECIFIED
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Caltech Tectonics Observatory120
Issue or Number:9-10
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15121
Deposited By: George Porter
Deposited On:08 Sep 2009 16:43
Last Modified:03 Oct 2019 00:55

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