Re-interpretation of progressive metamorphism, facies series, P-T-t path and exhumation model for the collisional orogenic belts

Recent discovery of ultra-high pressure (UHP) mineralogy, and descriptions of geology, petrology, geochronology and geochemistry of the Phanerozoic collisional orogens have changed the basic concepts of metamorphic facies series, P-Ttime path, progressive metamorphism, Barrovian-type metamorphism and tectonic model. The Himalayan orogen has served as a world standard for the collisional orogenic belt for a long time, characterized by Barrovian-type metamorphism (intermediate-P type metamorphism within the stability field of plagioclase), tectonic overlapping of double-continental crust, and thermal relaxation with buoyant unroofing (England and Thompson 1984). Recent discovery of coesite-bearing eclogite in the western Himalaya and eclogites from the central to eastern Himalaya can not be explained by the previous models. In the followings, summarizing the new constraints on orogenic process, I try to explain the collision orogeny including Himalaya.