Timing of synorogenic granitoids in the south qinling,central China:constraints on the evolution of the qinling-dabie orogenic belt

摘要

The ca.400-km-long graintoid belt in the South Qinling is believed to be a synorogenic product of the collision between the North and South China Blocks along the Qinling-Dabie orogenic belt in central China.Single and multigrain zircon U-Pb dating of six of these granitoid bodies indicate that the granitoids wee formed between 220+-1 and 205+-1 Ma,supporting the idea that the collision between the North and South China Blocks happened in the Triassic.The formation of these synorogenic granitoids in the South Qinling is simila rin time but slightly later than the rapid exhumationof the ultrahigh-pressure metamorphic rocks and their country rocks in the eastern part of the Winling-Dabie orogen,suggesting a close relationship between the rapid exhumation of the ultrahigh-ressure metamorphic rocks in the Dabie Montains and the formation of the South Qinling granitoids.According to regional geology,the breakoff of a subducted slab,if there was any,should have occurred at a shallower depth in the South Qinling compared with that in the Dabie Mountains and Sulu terrane.This shallow breakoff is likely to have disturbed the asthenosphere seriously,leading to the melting of the overlaying lithosphere as well as the formationof the granitoid belt.