The 1.0 Ga S–type granite in the East Kunlun Orogen, Northern Tibetan Plateau: Implications for the Meso– to Neoproterozoic tectonic evolution

Abstract

The East Kunlun Orogen (EKO) is characterized by widely distributed granitoids with different ages, which are keys to understanding the tectonic evolution of the Central China Orogenic Belt. Zircon U–Pb ages and Hf isotopic compositions, as well as the whole rock geochemistry of the gneissic granite from the basement rock, are carried out to elucidate the Meso– to Neoproterozoic tectonics of the EKO. The Al–rich minerals, including muscovite and tourmaline, and the A/CNK ratios (1.07–1.18) indicate S–type affinity of the granite. The granite displays high SiO2 and K2O contents, and slightly enrichment in LREE in chondrite normalized REE distribution pattern with strong negative Eu anomalies (δEu=0.10–0.15). The samples exhibit positive anomalies of Rb, Th, U and Pb, and depletion of Ba, Nb, Ta, Sr and Ti. Meanwhile, the high Rb/Ba and Rb/Sr ratios and low (CaO+FeO+MgO+TiO2) contents indicate that they were derived from pelitic material. Together with the negative εHf(t) values ranging from −5.97 to −2.34 and two–stage Hf model ages varying from 1968 to 1786Ma, the gneissic granite is suggested being originally derived from partial melting of the metasedimentary rocks of the Paleoproterozoic Jinshuikou Group in the central EKO due to the crust thickening. Most zircon grains from the gneissic granite show typical magmatic zircon morphology, and yield an U–Pb upper intercept age of 1006±20Ma (MSWD=1.5), representing the crystallization age. Integrated with the regional geology, our results suggest that the EKO has been probably involved into a Meso– to Neoproterozoic plate collisional event related to the assembly of the Rodinia supercontinent.