The Mesozoic gabbro, diorite, granodiorite and granite are widespread at Chahannuo area in the north margin of Qaidam terrane. LA-ICP-MS zircon dating yields Middle Triassic age of 246±0.7 Ma for the Chahannuo gabbro. The gabbros have low SiO2(50.6%~54.41%), total alkali contents(2.36%~3.72%), and low σ value caring from 0.54 to 1.12, indicating that they are belong to medium-K calc-alkaline series. They are characterized by elevated high MgO, Mg#, Cr, Ni, enriched LREE, LILEs(U, Th, K), and depleted in HREE, HFSEs(Nb, Ta, Ti). The gabbro zircons εHf(t)changed from -2.24 to +1.37. These indicated that gabbros were dominatly derived by the partial melting of enriched lithosphere which had been metasomatism the fluid from the subducted slab. The Chahannuo gabbro were contemporary with the calc-alkaline magmatism from Buerhanbuda in the East Kunlun orogen, Elashan and Tongren-Zeku area in the West Qinling orogeny. These calc-alkaline magmatism constituted a active continental margin arc formed by the northern subduction of Paleo-Tethys Ocean.