摘要
A group of A-type granite has been found in recent years in the middle segment of the Bangonghu-Nujiang suture.These granite bodies occur as stocks with exposed areas of less than 1 km2.Lithologically,these A-type granites include two types of biotite granite and granodiorite porphyry,which intrude into Cretaceous sedimentary rocks.Zircon U-Pb LA-ICP-MS dating for the three granite bodies indicates that they formed in the late stage of the Early Cretaceous.From their zircon U-Pb ages and post-collisional A2-type signatures,the authors infer that the Bangonghu-Nujiang middle Tethys ocean should be closed at least in the beginning of Early Cretaceous.