Tectono-magmatic evolution from accretion to collision in the southern margin of the Central Asian Orogenic Belt

The global orogenic belts have undergone accretionary and collisional orogenic processes to varying degrees. Then, how accretion evolves into the collision is a frontier scientific question for plate tectonics and continental dynamics. The Central Asian Orogenic Belt (CAOB) is the largest Phanerozoic accretionary orogenic belt by the long-term subduction-accretionary evolution related to the Paleo-Asian Ocean. Its late evolution stage is relatively short of collision-related tectonic and metamorphic records. So, whether a collision-related magmatic record develops is still an open question. The magmas in the southeastern margin of the CAOB were characterized by calc-alkaline and alkali-calc and migrated from the northwest to the southeast. These magmas are also indicated by evolution from the Permian arc magma to the Early-Middle Triassic collision-related high Sr/Y magma derived from the old crust and A type granites associated with the Late Triassic post-orogenic extension. This study provides critical magmatic evidence for the evolution of subduction-accretion to collisional orogenesis. Combined with the regional geology, we have determined that the signature magma associated with the last collision of the CAOB is the high Sr/Y granite derived from the thickened lower crust and scattered linearly along the suture zone. A three-stage tectonic-magmatic evolution model from discrete bidirectional subduction-accretion to accretionary wedge-accretionary wedge-collision and post-orogenic extension was proposed in the southern margin of the CAOB. The collision-related magmatic records are distributed laterally from Beishan of Gansu Province to the central part of Jilin Province, indicating that the collision-related magmatism has good generality in the southern margin of the CAOB. The clarification of the magmatic evolution records from accretion to collision during the late CAOB evolution reveals that the largest Phanerozoic accretionary orogenic belt experienced different tectonic deformation of compress, strike-slip and extension at the end of its evolution. The development of collision-related magmatic records showing discernible linear distribution is of great significance for further exploration of the signature magmas at the end of accretionary orogenic evolution.