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Dome formation and extension in the Tethyan Himalaya, Leo Pargil, northwest India

Rasmus C. Thiede^,1, J. Ramón Arrowsmith^,2, Bodo Bookhagen^,3, Michael McWilliams^#,4, Edward R. Sobel^,5 and Manfred R. Strecker^,5

¹ Institut für Geowissenschaften, Universität Potsdam, Postfach 601553, Potsdam 14415, Germany
² Department of Geological Sciences, Arizona State University, Tempe, Arizona 85287-1404, USA
³ Institut für Geowissenschaften, Universität Potsdam, Postfach 601553, Potsdam 14415, Germany
⁴ Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115, USA
⁵ Institut für Geowissenschaften, Universität Potsdam, Postfach 601553, Potsdam 14415, Germany

Metamorphicdomecomplexesoccurwithin the internal structures of the northern Himalaya and southern Tibet. Their origin, deformation, and fault displacement patterns are poorly constrained. We report new field mapping, structural data, and cooling ages from the western flank of the Leo Pargil dome in the northwestern Himalaya in an attempt to characterize its post–middle Miocene structural development. The western flank of the dome is characterized by shallow, west-dipping pervasive foliation and WNW-ESE mineral lineation. Shear-sense indicators demonstrate that it is affected by east-west normal faulting that facilitated exhumation of high-grade metamorphic rocks in a contractional setting. Sustained top-to-northwest normal faulting during exhumation is observed in a progressive transition from ductile to brittle deformation. Garnet and kyanite indicate that the Leo Pargil dome was exhumed from the mid-crust.

⁴⁰Ar/³⁹Ar mica and apatite fission track (AFT) ages constrain cooling and exhumation pathways from 350 to 60 °C and suggest that the dome cooled in three stages since the middle Miocene. ⁴⁰Ar/³⁹Ar white mica ages of 16–14 Ma suggest a first phase of rapid cooling and provide minimum estimates for the onset of dome exhumation. AFT ages between 10 and 8 Ma suggest that ductile fault displacement had ceased by then, and AFT track-length data from high-elevation samples indicate that the rate of cooling had decreased significantly. We interpret this to indicate decreased fault displacement along the Leo Pargil shear zone and possibly a transition to the Kaurik-Chango normal fault system between 10 and 6 Ma. AFT ages from lower elevations indicate accelerated cooling since the Pliocene that cannot be related to pure fault displacement, and therefore may reflect more pronounced regionally distributed and erosion-driven exhumation.

Key Words: Himalaya • Tibet • extension • dome • geochronology • exhumation

This article has been cited by other articles:

				J. E. Saylor, J. Quade, D. L. Dettman, P. G. DeCelles, P. A. Kapp, and L. Ding The late Miocene through present paleoelevation history of southwestern Tibet Am J Sci, January 1, 2009; 309(1): 1 - 42. [Abstract] [Full Text] [PDF]