Ocean−Continent Transition Process and Magmatism in Orogenic Belts: A Case Study of Paleozoic Granites in the Dulan Area of East Kunlun

The subduction−collision (accretion)−post−collision stages in the ocean−continent transition process have different magmatisms, among which the slab subduction and lithosphere delamination−thinning mechanisms have received special attention. The East Kunlun orogenic belt is located in the northern part of the Qinghai−Tibet Plateau, and is an important part of the Qin−Qi−Kun central orogenic belt, which has experienced the transformation process of the Proto−Tethys Ocean and Continent in the Early Paleozoic. Based on the geochronology, whole−rock geochemistry and Sr−Nd−Hf isotope studies of the Paleozoic granites in the Dulan area, eastern Kunlun, this paper suggests that the Langmuri Middle Silurian (429±4 Ma) granites were formed in the subduction stage of the oceanic crust. It has the property of adakitic island arc magma, which is related to the partial melting of oceanic crust under the mechanism of thermal subduction. The Xiwanggou and Harizha Early Devonian (416 ~ 403 Ma) granites were formed in the post−collision stage, showing the characteristics of I−type and A−type granites, respectively, which are related to the partial melting of the young lower crust and thinning of the lithosphere. The comprehensive regional Paleozoic granite geochemical data indicate that the difference of magmatic rocks in the east and west of East Kunlun may be caused by ocean ridge subduction.