Abstract:The BangonghuNujiang suture zone in Tibet of China. has been is an important porphyry copper gold metallogenic belt,with superior geological condition of mineralization, The Duolong oreconcentrated deposit, the first superlarge epithermal porphyry CuAu deposit discovered in the western BangonghuNujiang suture zone, is widely covered with plenty of effusive volcanic rocks. However, the petrogenesis, magma source and geodynamic setting of the granitoids are still constrained loosely. In this paper, LAICPMS zircon date yields UPb age of 108.2±2.6Ma(MSWD=0.39) for the dacite,regarding to the similar geochronological data of 109.3±2.2Ma(MSWD=1.70) for the rhyolite. The dacite and rhyolite are characterized by high silica(SiO2=60.89%~72.00%),potassiumrich(K2O =3.08%~5.53%),alkalirich (K2O+Na2O=6.88%~8.96%),peralkaline to peraluminous (A/CNK= 0.92~1.28) and High calcalkaline to shoshonitic. The rocks are systematically more enriched in largeion lithophile elements (LILE: Th、U、K、Pb and Rb) and LREE, relatively deplted in high strength elements (HFSE:Ta、Nb、Ti and Zr) and HREE. Total Coneentartion of REE range from 141.52×10-6 ~ 236.05×10-6, with LREE/HREE of 8.54~9.30, LaN/YbNof 10.42~11.05 and middle negative Eu anomalies(δEu=0.65~0.80).Besides, trace elements compositions indicate that the magma is contaminated by crustal mantle when it rise and The isotopes of these rocks are characterized by high(87Sr/86Sr)i(from 0.7050 to 0.7053), low (143Nd/144Nd)i(from 0.5124 to 0.5126,low εNd(t)(from -1.51 to 1.29). The positive εHf(t) values of zircons from rhyolite whose second stage Hf mode mean ages are 288.0Ma vary from +11.6 to +15.5, contrasted with εHf(t)values of +3.4~+8.0 from dacite whose second stage Hf mode mean ages are 8131Ma. Based on the above discussions, we proposed that the geochemical characteristics of these volcanic rocks are consistent with those of arctype magmas worldwide and the arc volcanic rocks magma were all generated by partial melting of mantle wedges replaced by the fluid which is formed the dehydration of the oceanic crust subduction plate, and its rockforming resulted from the mixing between the juvenile lower crustderived melts and mantlederived mafic melts under the background of BangonghuNujiang Tethys subducting northward to Qiangtang massif. In addition, the volcanic activity suggests BangonghuNujiang ocean was subducting at least during approximate 108~109Ma, and the closure time of this ocean should be later than early Cretaceous(108~109Ma), which is different from early recognition of closure time of late Jurassic to earlyCretaceous.