Study On The Petrogenesis, Tectonic And Ore-controlling Significance Of Caledonian And Indosinian Granite From Wulonggou Area In The Eastern Kunlun, Qinghai Province

The EKO is divided into the fault-bound North Kunlun belt, Middle Kunlun belt, and South Kunlun belt. The Wulonggou area is located in the central part of Middle Kunlun belt. Two ophiolite belts lay along the Middle Kunlun Fault and South Kunlun–Aryan Maqin Fault, which represent suture zones of the Proto-Tethys and Palaeo-Tethys oceans, respectively. Widespread granitic rocks were emplaced in Wulonggou area, and orogenic gold deposits, and skarn-type Cu-Pb-Zn mineralization are present in Wulonggou area.The detailed LA-ICP-MS zircon U-Pb dating and geochemical researches of Wulonggou Granodiorite, Xiaoyakou Granite and Houtougou monzogranite shows that the Houtougou monzogranite yieldyed a weighted mean 206Pb/238 U age of(419.0±1.9) Ma. And it has high Si O2, K2 O, Y, Yb contents and low Al2O3, Sr contents, with slightly negative Eu anomalies, relatively enriched in Rb, Th, U, La, Ce, Nd, depleted in high field incompatible elements Nb, Ta, and strongly depleted in Ba, Sr, P, Ti, which shows Granite gentic type of Houtougou is A2 type. So it was concluded that the closure of Proto-Tethys ocean in the East Kunlun area should not be later than the end of the late Silurian(~419 Ma), instead of the early Devonian previous thought. The Wulonggou Granodiorite which were previously considered to be Neoproterozoic in age yielded age of 247 ± 2, 248 ± 1 and 249 ± 1 Ma; The granodiorites of Wulonggou are metaluminous with an alumina saturation index of 0.90–0.96, low Fe2O3T/Mg O ratios and low Zr+Nb+Ce+Y contents, which suggest an I-type classical island arc magmatic source. The Xiaoyakou granite which were previously considered to be Neoproterozoic yielded weighted mean 206Pb/238 U age of 246 ± 3 Ma. The granites are peraluminous with an alumina saturation index of 1.02–1.03,(La/Yb)N values of 16.98~25.07, Sr/Y ratios of between 17.68 and 28.77, negative HREES(Yb = 1.10~2.00 ppm), and low Y(13.00~21.10 ppm), which suggest adakite-like rocks. All above show that Wulonggou Granodiorite and Xiaoyakou Granite was generated during the northward subduction of the Palaeo-Tethys oceanic plate.The zircon Hf Isotopic systematic of Houtougou demonstrates that their εHf(t) values range from 0.2 to 5.1 with the model age(TDM2) of 1066 to 1371 Ma. It was suggested that their primary magma was likely derived from partial melting of Mesoproterozoic mafic lower crust. These Hf isotopic data of Wulonggou Granodiorite demonstrates that their εHf(t) values range from-2.9 to +3.9, with the model age(TDM2) of 997 to 1436 Ma. These Hf isotopic data of Xiaoyakou Granite demonstrates that their εHf(t) values range from-7.8 to +3.2, with the model age(TDM2) of 1047 to 1735 Ma.They 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.