Petrogenesis Of Laojunshan And Taishanmiao Granite Plutons In Eastern Qinling, Central China

The eastern Qinling ore belt is the largest molybdenum (Mo) in the world. In recent years, the forming age of Mo deposits and related granitoids have been constrained by molybdenite Re-Os dating and zircon U-Pb dating. To fully understand the feature of the magmatism, which is related to mineralization, and geodynamic setting in the eastern Qinling region, we focus on the process and origin of these magmas in this study. On the basis of the zircon U-Pb chronological, petrological, mineralogical and petrogeochemistry of Laojunshan pluton and Taishanmiao pluton, we want to not only constrain the forming process of plutons, but also establish the magma system regularities.The Taishanmiao pluton, which is located in the southern margin of the North China Craton (NCC), is divided into three stages. And their lithology are respectively medium-coarse-grained moyite, big-porphyry fine-medium-grained moyite and porphyraceous fine-moyite. The zircon U-Pb ages of the three intrusive stages suggest that magma system lasts several Mas from125Ma to113Ma. The rocks are characterized by high silica, high alkali and low MgO, and enriched in Rb, Th, and U, and depleted in P, Ba, Sr, Ti and Eu. Moreover, the rocks have highly fractionated trace element ratios of Nb/Ta and Y/Ho. According to the feature of trace elements, the zircons from the pluton are divided into two types, the one is representive with high U contents, low Th/U ratio, high Y/Ho ratio and high Nb contents, which is similar to that in aqueous systems in which chemical complexation was of significant influence, and the other is relatively low U contents, high Th/U ration, normal Y/Ho ratio and low Nb contents. Futhermore, apatites in the rocks record complex processes, which contain stable crystallization in magma system and interaction between magma and aqueous-like fluid. We also surprisingly observe lanthanide tetrad effects in aptatite REE pattern, which reflects same information from high U zircon. Rocks have εNd(t) values ranging from-16.1to-7.5and TDM ages of1.19-2.01Ga, combining with all the zircon Hf isotopic data in the southern margin of the NCC, it can be deduced that Taishanmiao pluton results from a strong mantle-crust interaction.Laojunshan intrusive complex in Luanchuan county of Henan province, is located in the north Qinling tectonic belt and at the junction of the south margin of NCC. The rocks are characterized by high silica, high alkali and low MgO, and enriched in Rb, Th, and U, and depleted in P, Ba, Sr, Ti and Eu. According to the field lithology, major and trace elemental, we confirm that Laojunshan pluton represents a high evolved magma system. Based on tendency, Sr-Nd-Hf isotopic composition varies with ages, we deduce that Laojunshan pluton derives from partial melting of juvenile crust in Mesozoic.Highly fractionated trace element ratios of Y/Ho is often observed in porphyry system related to mineralization in the eastern Qinling region, this suggests that interaction between magma and aqueous-like fluid is an essential feature of Mo-bearing granitoids. Considering the end of mantle uplifting and the starting of magmatism in the eastern Qinling region are concurrent, we assume that asthenosphere upwelling and lithosphere delamination are the main causes of the late Mesozoic magma activity in this area.