Abstract: The Zhanarigen rock masses in Zhidoi, Qinghai consist of early biotite quartz diorite and late granodiorite. The granodiorite gives U-Pb zircon ages ranging between 216 ±2 Ma and 217 ±7 Ma (Late Triassic). The Zhanarigen rock masses are enriched in alkali and depleted in Ti, suggesting the calc-alkaline series. They also exhibit the enrichment of the macro-ion lithophile elements K, Ba and Rb, and high field strength elements Th, while slight depletion in Sr, Nb and Ta, marked depletion in Ti and P relative to their adjacent elements. The initial ⁸⁷Sr/⁸⁶Sr ratios vary from 0.70403 to 0.70463, and the ε_Nd(t) values from 2.7 to 3.4. Judged from the trace element discrimination diagrams, the Zhanarigen rock masses should be assigned to the volcanic arc granites derived from the mixed crust-mantle products.