Identification of A-type granite in the southeastern Kunlun Orogen, Qinghai Province, China: implications for the tectonic framework of the Eastern Kunlun Orogen

The Dalijigetang syenogranite in the eastern section of the Eastern Kunlun Orogen (EKO), China, is rich in SiO2 and alkali elements, has high FeOT/MgO ratios and is strongly depleted in CaO and MgO. Chondrite-normalized REE patterns show light REEs enrichment, heavy REEs depletion and negative Eu anomalies (delta Eu = 0.43-0.53). The 10(4)Ga/Al values range from 2.69 to 10.31. The combined total concentrations of Zr, Nb, Ce and Y (mean = 420.04 ppm) indicate that the Dalijigetang syenogranite is an A-type granite. The zircon epsilon(Hf)(t) values relatively are all moderately negative (-6.1 to -10.7), and the model ages (t(DM2)) range from 1666 to 1960Ma (mean = 1801 Ma), which is much older than zircon U-Pb ages (259 Ma). Based on integrated isotopic and geochemical data, we infer that the syenogranite formed by the partial melting of lower crustal material under low-pressure and high-temperature conditions. Based on the above data, combined with the regional geological background, we conclude that the Dalijigetang A-type syenogranite formed during an end-early Permian period of extension between two episodic subduction events within the EKO. This suggests that the onset of northward subduction of the Palaeo-Tethyan Ocean plate might have commenced as early as the early Permian. Copyright (C) 2016 John Wiley & Sons, Ltd.