U-Pb chronology, geochemical characteristics and petrogenesis of the Chelugou pluton in the western part of North Qilian orogenic belt

Located at the westernmost end of the North Qilian orogenic belt, the Chelugou pluton consists predominantly of quartz diorite porphyry and diorite porphyry. Zircon LA-ICP-MS U-Pb dating of the Chelugou quartz diorite porphyry yielded an age of (462.1±3.8) Ma. Rocks from the Chelugou pluton show intermediate-felsic, metaluminous and low calc-alkaline features, with relatively low SiO₂ (61.44%-67.63%), Al₂O₃ (15.09%-16.7%) and A/CNK values (0.90-1.00), and high Na₂O/K₂O ratios (7.47-9.96). They have relatively low rare earth element content (33.40×10^-6-39.27×10^-6) and are characterized by positive Eu anomaly and high LREE/HREE ratios (3.95-6.51), similar to features of typical adakites. All of the rocks are also enriched in Ba, Sr and depleted in HFSEs (e.g., Nb, Ti and Yb). By comprehensively synthesizing geochemical compositions and geological setting for magma rocks within the study area, the authors hold that the Chelugou granitoids were derived from partial melting of subducted oceanic plate related to the northward subduction of the Qilian Ocean underneath the North China Block in Ordovician.