Thermal structure and exhumation history of the Lesser Himalaya in central Nepal

摘要

The Lesser Himalaya (LH) consists of metasedimentary rocks that have been scrapped off from the underthrusting Indian crust and accreted to the mountain range over the last ～ 20 Myr. It now forms a significant fraction of the Himalayan collisional orogen. We document the kinematics and thermal metamorphism associated with the deformation and exhumation of the LH, combining thermometric and thermochronological methods with structural geology. Peak metamorphic temperatures estimated from Raman spectroscopy of carbonaceous material decrease gradually from 520° - 550℃ below the Main Central Thrust zone down to less than 330℃. These temperatures describe structurally a 20°-50℃/km inverted apparent gradient.