The quartz diorite on the northwestern margin of Qaidam basin is characterized by high Al₂O₃,low Alk and Na₂O>K₂O,with alumina saturation index A/CNK being 0.87~0.91. These features suggest that this quartz diorite belongs to calc-alkaline peraluminous and metaluminous rocks. The chondrite-normalized REE show right-inclined patterns with slightly negative Eu anomaly,and the primitive mantle normalized trace element spidergrams are characterized by enriched LILE(such as Rb, Th and U), depleted HFSE(such as Nb, Ta, P and Ti), low Nb/La and Rb/Nb ratios, which are comparable with the characteristics of I-type granites. High CaO/Na₂O(2.32~2.64)ratios and diagrams show that the pluton was derived from remelting of the meta_morphic basalt in the lower crust. The initial temperature of magma was >768℃ by using whole rock Zr thermometer. Rock geochemical characteristics indicate that the pressure of the source region was probably>1.5 Ga, and the residual facies was correspondingly garnet+amphibole+rutil. Combined with the cathodoluminescence (CL) images and element features of zircon,this study yielded an age of 252±1 Ma for pluton using LA-ICP-MS zircon U-Pb dating. On the basis of regional geological evolution, the authors hold that Zongwulong oceanic crust subducted toward Oulongbuluke block in Late Permian.