The gneissic quartz diorite in northern Lenghu of Qinghai，is characterized by low SiO2，high Na2O，Al2O3 and MgO，with alumina saturation index A/CNK of 0.66~0.70. These features suggest that the gneissic quartz diorite belongs to the high-K calci-alkaline peraluminous rocks and metaluminous rocks. The chondrite-normalized REE shows rightinclined patterns with slightly negative Eu abnormity. The primitive mantle normalized trace element spidergrams are characterized by enriched LILE（such as Rb, Ba and Sr ） and depleted HFSE （such as Nb，Ta, Zr and Hf），as well as evidently high contents of Th and U，which are compatible with the characteristics of orogenic magmatic rocks. The rocks probably from volcanic arc tectonic setting，associated with subduction. Moreover，the gneissic quartz diorite are rich in Na2O and A12O3，high Sr, Sr/ Y（27.31~32.43）, CaO/Na2O and LREE，low Rb/ Sr（< 0. 1）, these believe that these rocks in northern Lenghu of Qinghai formed by the melting of middle—high K metabasaltic rocks with amphibole as a residual phase. With the U-Pb isotopic age of 430.7±0.8 Ma，we believe that when the oblique intracontinental subdction—collision was started between Qaidam and Tarim block，the movement of asthenosphere led to the lithospheric detached，simultaneously，the low density Qaidam quickly exhumated under the condition of buoyancy. With increasing temperature and decreasing pressuer , middle—high K metabasaltic rocks were melted, the gneissic quartz diorite was the record of exhumation for Qidam Ultra-Pressure Metamorphic Belt.