Petrogenesis Of Late Mesozoic Igneous Rocks,Beihuaiyang, Anhui Province:Implication For Tectonic Evolution

The Beihuaiyang region is located in the Qinling-Dabie orogen, which is characterized by extensively magmatic events. On the basis of the field work and microscopy study, and zircon U-Pb dating, wall-rock geochemistry, Sr-Nd-Hf isotopes, this paper focused on the Cretaceous igneous rocks by using. The magmatic zircon U-Pb dating yields the ages of121-132Ma. In addition, some inherited zircons obtain the ages of267-1799Ma, indicating the occurrence of regional tectonic thermal events. Major elements show that these igneous rocks are calc-alkaline granite and rhyolite, and alkaline quartz syenite, monzonite, and dacite-dacitic basalt. They mainly present high K calc-alkaline, even shoshonite, and weak peraluminous. Trace elements of regional igneous rocks reveal variable depletion. Meishan and Hongchong plutons exhibit Ba, Sr and Ti depletion; Taohualing, Sunchong and Baochong plutons, and Jingangtai volcanic rocks show Nb, Ta and Ti depletion; Lingjiachong and shanqi plutons and Xindianhe volcanic rocks display Nb, Ta, Zr, Hf and Ti depletion; Huagaishan and Hepeng plutons show Nb, P, Zr and Ti depletion. Rare earth elements in all igneous rocks exhibit that LREE enrichment. Meishan, Hongchong, Huagaishan and Hepeng plutons display Eu negative abnormalities, whereas others no obvious Eu abnormalities. The former indicate the origin of upper continental crust, the latter demonstrate the origin of much deeper magmatic sources. Sr-Nd isotopes display that these rocks have87Sr/86Sr(T) and εNd(T) compositions analogous to the rocks of North Dabie region, indicating similar magmatic sources. They have εHf(t) values of-30to-5in the Cretaceous magmatic zircons, and εHf(t) values of-22to-2in the older inherited zircons. The former data can be plotted into the region of the later results, indicating the Cretaceous magmatic rocks can be generated from the partial melting of the older crust. The Paleo-to Meso-Proterozoic two-stage Nd model ages (1.6-2.6Ga), and Archean to Meso-Proterozoic two-stage Hf model ages (1.7～3.2Ga), support the occurrence of old Archean to Meso-Proterozoic continental crust. Given that the Beihuaiyang region is located in the interior of the Eastern China, these Cretaceous igneous rocks probably are generated in intra-plate tectonic setting.