Geochemical characteristics,zircon U-Pb age,and Hf isotopes of Yushenkala pluton in western Junggar,Xinjiang:Constraint on the closure of Paleo-Asian Ocean

The Yushenkala pluton is located in the northern part of west Junggar Basin of Xinjiang and lies along the suture zonebetween Siberia plate and Junggar plate. Petrologically, the pluton consists of gabbro, hornblende gabbro, diorite and quartz diorite which intruded in the middle Devonian Yudoukala Group. LA-ICP-MS zircon U-Pb dating shows that the age of the hornblende gabbro is 364±1Ma, which represents the formation age of the pluon. The eHf(t) values of the zircon are in the range of 4.3-11.5,with a weighted average of 9.0±1.2, suggesting that its original rock was derived from mantle materials. The one-stage Hf model ages(TDM1) are 529-827 Ma(629±95 Ma on average), indicating an original rock of Cambrian- Precambrian basement. Based on field geological and geochemical characteristics, the authors infer that the pluton formed in an island-arc environment or active epicontinental environment. In the late Devonian, the arc magmatism was well developed, and the ocean-continent subduction event basically came to an end in the northwestern part of western Junggar. These data indicate that the closing time of Paleo Asian ocean was not earlier than 364 Ma.