The Thakhola-Mustang Graben of central Nepal represents the Cenozoic extensional tectonic phase of the Tibetan Plateau and the whole Himalaya. It is located on the northern side of the Dhaulagiri and Annapurna Ranges and south of the Yarlung Tsangpo Suture Zone. The graben is an asymmetrical basin containing thick (more than 850m) continental debris. Stratigraphically, the graben sediments are divided into four formations, namely the Tetang Formation, the Thakkhola Formation, the Sammargaon Formation and the Marpha Formation. The oldest sedimentary units are the Tetang and Thakkhola formations (Miocene) while the Sammargaon and the Marpha formations lying disconformably above these formations represent younger units (Plio-Pleistocene). The Thakkhola and Tetang formations are separated by a lowangled (_5
