A Re-look at the Himalayan metamorphism

Abstract

Regional metamorphic rocks preserve records of geodynamic evolution of orogenic belts. The Himalaya represents an evolving mountain belt with a complex geological history and is considered here as a composite of Trans-Himalaya and the Himalaya per se and the intervening Indus-Tsangpo Suture Zone. Each of these three tectonic domains is evaluated in the context of their metamorphic evolution. An episodic evolution is inferred and described. The beginning of the Himalayan orogeny is ascribed to the Cretaceous initiation of the suturing of the 'island arc' rocks with the Asian block, followed by underthrusting of the Indian block ~57Ma ago. Differences in metamorphism of underthrust and overthrust blocks are reflected in their P-T-t evolution. The exhumation along the strike length was unequal with significantly higher exhumation rates along the syntaxes. The anatectic melt produced at the time of the Tertiary age Himalayan metamorphism got emplaced within the Himalaya as well as within the Trans-Himalaya, possibly through crustal-scale faults such as the Karakoram fault.