Origin of the Heping granodiorite pluton: Implications for syn-convergent extension and asthenosphere upwelling accompanying the early Paleozoic orogeny in South China |
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| Institution: | 1. Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, Huibei Province, China;2. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, Huibei Province, China;3. The First Institute of Geological and Environmental Survey, Henan Bureau of Geology and Mineral Resources, Zhengzhou 450045, Henan Province, China;4. Institute of Geological Survey, Nanning 530023, Guangxi Zhuang Autonomous Region, China;1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, Guangdong China;2. University of Chinese Academy of Sciences, Beijing 10069, China;3. Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong;4. Department of Applied Geology, Curtin University, Perth WA 6845, Australia;1. School of Earth Sciences, Center for Global Tectonics, State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;2. Three Gorges Research Center for Geo-hazards, China University of Geosciences, Wuhan 430074, China;3. Department of Geological Engineering, Middle East Technical University, Ankara, Turkey;4. Department of Earth and Environmental Sciences, University of Windsor, Ontario, Canada |
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| Abstract: | We present geochemical and geochronological data of host granodiorites and mafic microgranular enclaves (MMEs) from the Heping pluton, which is situated in the central part of the Wuyi-Yunkai Orogen (WYO) in the South China Block (SCB), and reveal syn-convergent extension and asthenosphere upwelling during the early Paleozoic intracontinental orogeny. Two host and two MME samples from the Heping pluton yield LA-ICP-MS zircon U Pb ages of ca. 445 Ma, coincident with the peak magmatism-metamorphism of the WYO. The host granodioritic samples are metaluminous (A/CNK = 0.68–0.91) and have abundant amphibole and low-moderate SiO2 (59.1 to 67.3 wt%), belonging to high-K calc-alkaline I-type granite, whereas the MMEs are more basic with SiO2 of 56.3 to 59.6 wt%. Both the host and MME samples display weakly negative Eu anomalies and distinctly relative depletions of Ta, Nb, and Ti, and most of them share similar initial 87Sr/86Sr ratios of 0.7089–0.7112 and εNd(t) values of ?6.52 to ?7.12, except one MME sample with a lower initial 87Sr/86Sr of 0.70758 and a higher εNd(t) of ?4.33. The zircon εHf(t) values exhibit a wide range from ?13.68 to ?0.87. Petrological, geochemical, and chronological data suggest that the Heping pluton were generated by mingling of mafic and felsic magmas. The mafic endmember magma was originated mainly from the enriched subcontinental lithosphere mantle at the spinel–garnet transitional zone (~70 km), subsequently underplated/intraplated into the lower-middle crust resulting in the melting of the intermediate rock at pressure < 8 kbar to produce the felsic endmember magma. We proposed a new tectonic model “syn-convergent extension and asthenosphere upwelling during the intracontinental orogeny”. The syn-convergent extension zones, which include a series of NW-trending transverse faults and the NE-trending reactivated pre-exsiting suture and rift zone (i.e. Shaoxing-Jiangshan -Pingxiang- Chenzhou fault) within the WYO, are in favor of asthenosphere upwelling leading to intensive crust-mantle interaction. |
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