Neoproterozoic granitic gneiss offshore the Shandong Peninsula of Eastern China: the eastward extension of the Sulu Orogenic Belt |
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| Authors: | Baojing Yue He Zhang Xue Ding Xuebo Yin |
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| Institution: | 1. Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology, Ministry of Land and Resources, Qingdao Institute of Marine Geology, Qingdao, China;2. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China;3. Key Laboratory of Crust–Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, China;4. Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China |
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| Abstract: | The Sulu Orogenic Belt in eastern China has experienced a multistage tectonic evolutionary history. However, its geological evolution has not yet been corroborated by sufficient direct evidence from basement rocks. Chaolian Island on the Qianliyan Uplift provides an opportunity to study the formation and evolution of the Sulu Orogenic Belt using direct geochronological and geochemical evidence. We determined that the characteristic mineral assemblage in the study region is quartz + K-feldspar + perthite + biotite + muscovite. The samples are silica- (SiO2 = 72.8%–75.8%) and alkali-rich (ALK(Na2O+K2O) = 8.7%–9.3%), with high iron-magnesium ratios (FeO*/(FeO*+MgO) = 0.92–0.96) and low CaO and MgO concentrations. Furthermore, they are rich in large-ion lithophile elements K, Rb, Ba, and U, but depleted in high field strength elements Nb, Ta, and Zr. They exhibit high Ga/Al values (Ga × 104/Al = 3.33–3.74) and significant fractionation between light and heavy rare earth elements. The samples are A-type granites. In the discrimination diagrams for granite genesis types, the samples plotted in the post-orogenic A2-type granite region. Secondary ion mass spectrometer (SIMS) zircon U–Pb dating results indicated that the granitic gneiss formed ~782.6–802.3 Ma (Middle Neoproterozoic), consistent with the timing of the breakup of the Rodinia supercontinent on the northeastern margin of the Yangtze Plate. Comparing geochemical characteristics and zircon U–Pb ages of the A-type granitic gneisses of the Sulu Orogenic Belt, the Qianliyan Uplift appears to be an extension of the belt across the ocean and is affiliated with the Yangtze Plate. The granitic gneiss on Chaolian Island is related to the formation of a mantle superplume during the breakup of Rodinia, and the northeastern margin of the Yangtze Plate during the Middle Neoproterozoic was located in a back-arc extension setting induced by the subduction of oceanic plates. |
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| Keywords: | A-type granitic gneiss geochemistry Neoproterozoic Sulu Orogenic Belt zircon age |
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