Characteristics and tectonic significance of the Zhanarigen rock masses in Zhidoi, Qinghai

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.