LA-ICP-MS zircon U-Pb dating of the porphyaceous syenogranite in Niuxinshan along the central segment of North Qilian orogenic belt and its geological significance

The porphyaceous syenogranite pluton is exposed in the west of Qilian Country, Qinghai Province. The authors conduct-ed LA-ICP-MS zircon U-Pb dating of the porphyaceous syenogranite and the result shows that the age is 166.6±2.4Ma, suggesting the Middle Jurassic of Yanshanian period. Several inheritable magmatic zircons yielded the age information of the Precambrian peri-od. Geochemical data show that the porphyaceous syenogranite is silica-enriched in composition with high content of alkali, and hence it is a peraluminous granite and belongs to the high-K calc-alkaline series. It is characterized by enrichment of Rb, Th, K, de-pletion of Ba, Nb, P, Ti, and weak negative anomaly of Eu, with the average Rb/Sr ratio being 1.86, which reflects the characteris-tics of the crust source and indicates S type granite.