Zircon U–Pb geochronology and Hf isotopic constraints on the petrogenesis of Early Triassic granites in the Wulonggou area of the Eastern Kunlun Orogen, Northwest China

Abstract

AbstractWidespread granitic intrusions in the northeast part of the Wulonggou area were previously thought to be emplaced into the Palaeoproterozoic Jinshuikou Group during the Neoproterozoic. This contribution presents detailed LA-ICP-MS zircon U–Pb geochronology, major and trace element geochemistry, and zircon Hf isotope systematic on the Wulonggou Granodiorite and Xiaoyakou Granite from the Wulonggou area. Three granodiorite samples yielded U–Pb zircon ages of 247 ± 2, 248 ± 1, and 249 ± 1 Ma, and one granite sample yielded U–Pb zircon age of 246 ± 3 Ma. The granodiorite samples are metaluminous with an alumina saturation index of 0.90–0.96, as well as intermediate- to high-alkali contents of 5.49–6.14 wt.%, and low Zr+Nb+Ce+Y contents, and low Fe2O3T/MgO ratios, which suggest an I-type classical island arc magmatic source. The granite samples are peraluminous with an alumina saturation index of 1.02–1.03, Sr content of 305.00–374.00 ppm, Sr/Y ratios of between 17.68 and 28.77, (La/Yb)N values of 16.98–25.07, low HREEs (Yb = 1.10–2.00 ppm), and low Y (13.00–21.10 ppm), which suggest adakite-like rocks. All granodiorite samples have zircons εHf(t) values ranging from −2.9 to +3.9, and granite samples have zircon εHf(t) values ranging from −7.8 to +3.2. These Hf isotopic data suggest that the Early Triassic granites were derived from the partial melting of a mafic Mesoproterozoic lower crust, although the degree of ancient crustal assimilation may be higher for the Xiaoyakou Granite. It is suggested here that the ca. 246–248 Ma magma was generated during the northward subduction of the Palaeo-Tethys oceanic plate.Keywords: Early Triassic granitic rockszircon U–Pb geochronologyzircon Hf isotopepetrogenesisWulonggou areaEastern Kunlun Orogen AcknowledgementsThanks are due to the Fifth Geological Prospecting Institute in Qinghai Province, and First Institute of Qinghai Geology Survey, China. We are grateful to Dr Hou Minglan, Lin Peijun at the Analysis Centre in the Shandong Bureau of China Metallurgical Geology Bureau and Dr Yang Tao from the State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, in Nanjing University for their great help with the lab work of LA-ICP-MS zircon dating and the LA-MC-ICP-MS in situ Hf isotopic analyses, etc. We also want to thank Mr Li Shijin, Deng Yuanliang, and Zhang Yanlin et al. for their assistance during fieldwork, and Dr Leon Bagas at the University of Western Australia for his linguistic assistance and some valuable suggestions. We thank the Editor-in-Chief and two anonymous reviewers for their thoughtful reviews. Their constructive, stimulating, and valuable comments and suggestions helped improve the manuscript significantly.ORCIDQing-Feng Ding http://orcid.org/0000-0001-8355-417XAdditional informationFundingThis work was supported by China Natural Sciences Foundation [grant number 40802021]; Fundamental Research Funds for the Central Universities in China [grant number JCKY-QKJC34]; and Postdoctoral Research Grant of Nanjing University [grant number 17–1112–4].