Petrogenesis and tectonic evolution of Lianyunshan complex,South China: Insights on Neoproterozoic and late Mesozoic tectonic evolution of the central Jiangnan Orogen |
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| Institution: | 1. State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing 210093, PR China;2. Department of Earth Sciences, University of Adelaide, Adelaide, SA 5005, Australia;3. School of Earth Sciences and Resources, China University of Geosciences Beijing, No. 29, Xueyuan Road, Haidian District, Beijing 100083, PR China;1. State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing 210093, Jiangsu, China;2. State Key Laboratory of Geological Processes and Mineral Resources, Collaborative Innovation Center for Exploration of Strategic Mineral Resources, Faculty of Earth Resources, China University of Geosciences, Wuhan 430074,China;3. Max-Planck-Institut für Chemie, Hahn-Meitnerweg 1, D-55128 Mainz, Germany;4. Lamont-Doherty Earth Observatory of Columbia University, P.O. Box 1000, Palisades, NY 10964, USA;5. Faculty of Land Resources and Engineering, Kunming University of Science and Technology, Kunming 650093, Yunnan, China |
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| Abstract: | The Yangtze and Cathaysia blocks in South China are separated by the ca. 1500 km long Jiangnan Orogen. The Lianyunshan complex, located in the central segment of Jiangnan Orogen, includes wide exposures of late Mesozoic granites. Here we report geological, geochronological and geochemical data from the Lianyunshan late Mesozoic granites and their Neoproterozoic host rocks belonging to the Lengjiaxi Group. Detrital zircon U–Pb ages reveal a single prominent peak at ca. 840 Ma in the metamorphosed and deformed Lengjiaxi Group samples. Ten of the youngest zircon grains in these rocks have a weighted mean age of 828.8 ± 7.1 Ma, which is tentatively interpreted as the maximum depositional age of the Lengjiaxi Group. Two stages of late Mesozoic S-type granites are dated at ca. 150 Ma and ca. 140 Ma from the Lianyunshan domain. From early to late, these rocks show decreasing MgO, CaO, Fe2O3T, TiO2 contents and increasing SiO2, K2O, Eu/Eu*, Rb/Sr ratios and differentiation index, suggesting continuous magmatic evolution dominated by fractional crystallization. The εHf(t) values of zircons with late Mesozoic ages are all negative, with their two-stage model ages mainly ranging from 1.9 to 1.4 Ga, which is significantly different from the model age of the host rocks belonging to the Lengjiaxi Group. These results indicate that the late Mesozoic granites were mainly derived from the partial melting of Paleo-Mesoproterozoic basement rocks that are older than Lengjiaxi Group. Major and trace element features suggest that the protoliths of these early stage granites in Lianyunshan are probably mixed greywacke and shale. The arc-like trace elements signature of all the late Mesozoic granites were possibly inherited through crustal contamination during the magma genesis caused by slab rollback associated with Paleo-Pacific subduction during 150- to 140 Ma beneath the central Jiangnan belt. |
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