Metamorphism and magmatism during the Himalayan collision

Abstract

Collision of India and Eurasia occurred sometime during the Eocene following the Tethyan oceanic subduction. Post-collision metamorphic and magmatic events in Tibet and in the Himalaya are reviewed. Metamorphism is limited to the Himalaya where at least four zones may be recognized which from S to N are, (i) high-pressure metamorphism produced before, but emplaced, during obduction, (ii) a belt of low-grade metamorphism produced during the first nappe emplacement, (iii) the pre-granitic Barrovian metamorphism of the High Himalaya, and (iv) the inverted metamorphism induced during shearing along the Main Central Thrust. Magmatism in the Himalayan domain resulted in two parallel belts of granitoids that were generated in the same way but differ in their mode of emplacement. In Tibet, magmatism spread over most of the domain following collision and magma is probably present now at shallow depths. The relationship between crustal thickening, uplift and magma generation is not clear. The difference in metamorphic and magmatic characteristics in the two domains may help to trace palaeocollision zones.