Retrograde metamorphism and tectonic emplacement of high pressure metamorphic belt in central Qiangtang Tibet

The high pressure metamorphic belt, located in central Qiangtang Tibet, is mainly composed of eclogite, garnet-phengite schist and blueschist. They underwent the exhumation after high pressure metamorphism and tectonically emplaced into the Late Paleozoic epimetamorphic rocks. The high pressure metamorphic belt contacts with epimetamorphic rocks by a ductile deformed zone. In this paper, based on studies of both the eclogite and the ductile deformed zone, exhumation age and retrograde metamorphic characteristics are discussed. It is proved that the eclogite underwent retrograde metamorphic evolution after peak metamorphism, from eclogite facies, blueschist facies to epidote-amphibolite facies. Ar- Ar dating of muscovite from muscovite-quartz schist, in the ductile deformed zone, obtains the plateau age of 219±2Ma, which represents the emplacing age of the high pressure metamorphic belt into the strata of Zhanjin Formation. Moreover, they were uplifted toward surface before 214Ma ago.