Yumuquan granitoid complex, located in the south margin of Altyn Tagh, northwestern China, contain many of melanocratic magmatic enclaves (MME), and its petrology and geochemical characteristics indicating the mixing between acid magma and more mafic magma in liquid phase, which belong to the corresponding period. The LA-ICP-MS zircon U-Pb isotopic dating show that the age of Yumuquan granite is 496.9±1.9Ma (MSWD=0.68), corresponding with the ages of ultrahigh-pressure metamorphic rocks (509~487 Ma )exposed at south Altyn Tagh.and the geochemical characteristics of the granitoid show high Al2O3(ave.15.88%), K2O/Na2O ratios (avg. 1.26),Sr(ave.446×10-6),（La/Yb）N ratios（24.04）and Sr/Y ratios（avg. 40）,and very lower Y(avg. 14.0 ×10-6)and Yb（avg. 1.5×10-6）, similar to high Sr and lowerY(Yb) type potash granite derived from thickened lower crust , So, The southern Altyn orogen belong to continental collision orogeny during ~500Ma, this collision rifting made the crust thickened and overlay each other. We consider that, the crustal thickening at Later Cambrain (~500Ma) in the area of south Altyn Tagh caused the lower crust part melt and product acid magma, at the same time, there are under plating of mantle-derived mafic magmas, The reason may be related to the rise of the deep hot mantle, which caused by the same period of continental deep subduction.