Mountain building in the Nepal Himalaya: Thermal and kinematic model

Abstract

We model crustal deformation and the resulting thermal structure across the Nepal Himalaya, assuming that, since 20 Ma, shortening across the range has been primarily taken up by slip along a single thrust fault, the Main Himalayan Thrust (MHT) Fault, and that the growth of the Himalayan wedge has resulted mainly from underplating and to the development of a duplex at midcrustal depth. We show that this process can account for the inverse thermal metamorphic gradient documented throughout the Lesser Himalaya (LH), the discontinuity of peak metamorphic temperatures across the MCT, as well as the distribution of age of exhumation across the range. This study suggests that the metamorphic evolution of the range over about the last 20 million years is compatible with the kinematics of recent crustal deformation deduced from morphotectonic and geodetic studies.