Geochemical and Chronological Characteristics of Early Silurian Granitic Rocks from the Upper-middle Reaches of Tataleng River in Qinghai

The granitic rocks from the Upper-middle Reaches of Tataleng River in Qinghai are mainly porphyritic monzonitic granite, monzonitic granite, granitic porphyry and porphyritic syengranite, which are syengranite, rapakiwi granite, granodiorite porphyry and quartz diorite. Geochemical study of these granitic rocks indicate that they are characterized by peraluminous (A/CNK=1.10~1.26) and high-K (K₂O > Na₂O), belonging to calc-alkaline series (σ=1.22~2.22) and S-type granite. LA-MC-ICP-MS zircon U-Pb results show that their ages are 440.4+1.4Ma. Tectonie setting discrimination diagram suggests that these granitic rocks were formed in post-collision tectonic environment. The comprenensive analysis indicates that the Early Silurian granite was formed by the partial melting of continental crust that caused by the extrusion of South Qilian block, when the South Qilian block was subducted and collided with the Quanji block in the continent-continent convergence stage.