Huangl shan area is located in the western part of the orogenic belt of the northern margin of the Qaidam Basin.Granite is widely distributed in the area.It is relatively deficient in isotope research results and geological records of magmatic activity and metamorphism.Methods: In this paper,we carried out some researches of the oligoclase granite porphyry intrusion by petrography,geochronology,geochemistry and whole-rock Sr-Nd isotopes,and explores its genetic type and source area, and discuss its geodynamic significance on this basis.Results: The result of LA-ICP-MS zircon U-Pb dating indicate that the crystallization age of the Huangl shan oligoclase granite porphyry is 466± 3 Ma,which is the product of the Caledonian Middle Ordovician.The samples have the characteristics of high SiO2,Na2O and low K2O.On the SiO2—K2O diagram,except for one sample falling into the calc—alkaline region,the rest of the samples fall into the tholeiitic series.The results show enrichment in right-leaning rare earth elements,and ((La/Yb)N range between 4.41 ~ 10.01).The samples have a low 10000Ga/Al(< 2.6) and a very low P2O5(average 0.06 %),indicating that the Huangl shan oligoclase granite porphyry is type I granite.Conclusions: Combined with Nd two-stage Nd model ages (1.03~1.21 Ga) of the Mesoproterozoic,the Huangl shan oligoclase granite porphyry is considered to be the product of the partial melting of the lower crust during the Mesoproterozoic reactivation.In the granite structure diagram,the samples fall into the VAG area,which indicate that formation of these granites is closely related to the subduction of oceanic crust.Combined with its associated relationship with the Ordovician Tanjianshan Group and the characteristics of Himalayan type granite,this paper suggests that the Huangl shan oligoclase granite porphyry be occurred in the back-arc basin environment related to oceanic crust subduction.The existence of back- arc basin implies that the subduction of oceanic crust was not over,and the terrane collision did not began.Therefore,the oceanic basin in the northern margin of Qaidam Basin was not closed at least 466 Ma.