U-Pb Ages and Geochemistry of Maozangsi Granodiorite in North Qilian Mountains, China

This paper reports a detailed study of petrology, U-Pb zircon dating and geochemical characteristic for Maozangsi granodiorite in North Qilian Mountains. The Maozangsi pluton is mainly consisted of granodiorite, and the SHRIMP U-Pb zircon dating yield a magma crystallization age of (456±3)Ma for this pluton. The Maozangsi granodiorite has high SiO₂ (65.1%~73.0%) and low Mg^# (18~32) values, its K₂O/Na₂O ratio is 0.82~1.37 while its A/NKC ratio is 0.9~1.1, belonging to high K calc-alkaline granite. It is rich in LILE and depleted in HFSE. The REE data shows strongly frantionated REE patterns, with (La/Yb)_N ratio of 11.1~34.1 and δEu value of 0.6~0.8. The geochemical characteristics and evolutionary history of granitoids in North Qilian orogen belt indicate that the magma of the granodiorite was derived from partial melting of basaltic rock in lower crust and formed in collisional tectonic setting.