Geologists at home and abroad have done a lot of research on the evolution of the Paleo-Tethyan ocean in the Changning—Menglian suture zone,but there is still a lack of precise chronological constraints on the end time of post collisional orogeny after its closure.We study the emplacement age,genetic type and material source of Qingtoushan granite,located in the northern part of Lincang magmatic arc,in Fengqing area,western Yunnan Province,so as to constrain the post collisional orogeny after the closure of Changning—Menglian ocean basin.Methods: Combined with the results of 1∶50000 and 1∶250000 Regional Geological and Mineral Survey Projects in recent years,we studied the petrology,geochemistry and LA-ICP-MS zircon U-Pb dating of mylonitized biotite monzogranite exposed in the Qingtoushan area,providing evidence for the structural evolution of the Changning—Menglian suture zone.Results: The LA-ICP-MS zircon U-Pb dating of the Qingtoushan granite yielded a magma crystallization age of 213 ± 5 Ma (mswd = 3.4,n= 14),which is attribute to characteristics of typical oscillatory zoning,and Th / U ratios greater than 0.2.The granite belong to peraluminous high-K calc-alkaline series,with low Na2O / K2O ratio,rich in Al2O3,and the average Al saturation index A / NCK is 1.18.The REE distribution curves have the characteristics of right deviation LREE enrichment,weak depletion on HREE,and obviously negative anomacies of Eu (δEu = 0.36～0.50). The granites enriched lithophile elements Rb,K and the high field strength elements such as Zr depleted.In the Rb—(Y+Nb) discrimination diagrams of trace elements, the projection points fall into the post-COLG,which have the characteristics of obviously transformed to intraplate granite.Conclusions: The crystallization age of 213±5 Ma indicates that the Qingtoushan granite was formed in the Late Triassic rather than the Permian.It is the youngest acid magma with the dual properties of post collisional granite and intraplate granite discovered in the Lincang magmatic arc so far,suggesting that the Changning—Menglian suture zone has entered the intracontinental extension stage,and the tectonic environment at that time has changed from compressional collision to extensional one.This age may provide constraints on the end of post collisional orogeny after the closure of Changning—Menglian Paleo-Tethys ocean.