The geology of Nepal is dominated by the Himalaya, the highest, youngest and a very highly active mountain range. Himalaya is a type locality for the study of on-going continent-continent collision tectonics. The Himalayan arc extends about 2,400 km (1,500 mi) from Nanga Parbat (8,138 m (26,699 ft)) by the Indus River in northern Pakistan eastward to Namche Barwa (7,756 m (25,446 ft)) by the gorge of the Tsangpo-Brahmaputra in eastern Tibet.[1] About 800 km (500 mi) of this extent is in Nepal; the remainder includes Bhutan and parts of Pakistan, India, and China.
Since 55 Ma the Himalayan orogeny beginning with the collision of Indian subcontinent and Eurasia at the Paleocene/Eocene epoch,[2] has thickened the Indian crust to its present thickness of 70 km (43 mi).[3] The northwest tip of India after colliding with Asia seems to have met along the full length of the suture by about 40 Ma.[4]
Immediately prior to the onset of the Indo-Asian collision, the northern boundary of the Indian shield was likely a thinned continental margin on which Proterozoic clastic sediments and the Cambrian ±Eocene Tethyan shelf sequence were deposited.[1]