When did the metamorphic nappe cover the Lesser Himalayan authochton? An approach from study on thermal history of Proterozoic granitic rocks and Miocene fluvial sediments

Abstract

The timing of exhumation of the Higher Himalaya Crystalline (HHC) is well dated in the Nepal Himalaya by dating of various metamorphic minerals of the MCT zone and the Higher Himalayan Crystalline. Previous studies indicate that rapid exhumation of the HHC occurred at around 25 to 13 Ma, and reactivation of the MCT occurred in Pliocene at 6 to 3 Ma. Exhumation of the HHC gave rise to southward advancement of crystalline nappe (Lesser Himalayan Crystalline: LHC) which tectonically covered the Lesser Himalayan authochthon over 100 km. However, it is not well understood when and how did the metamorphic nappe cover the authochton and when did the metamorphic nappe reach southern margin of the Lesser Himalaya just to the north of the Main Boundary Thrust (MBT). In order to solve these problems, we have started investigation of thermal history of the Lesser Himalayan autochthon and overlying low-grade metamorphic nappe in western and eastern Nepal Himalaya. This is the first report on the 40