The Triassic age for oceanic eclogites in the Dabie orogen: Entrainment of oceanic fragments in the continental subduction |
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| Authors: | Hao Cheng S. Andrew DuFrane Jeffrey D. Vervoort Eizo Nakamura Qiuli Li Zuyi Zhou |
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| Affiliation: | 1. Department of Earth Sciences, Durham University, Durham, DH1 3LE, UK;2. School of Earth Sciences, Lanzhou University, Lanzhou 730000, China;3. MOE Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China;4. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi''an 710069, China;1. CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;2. State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China;1. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China;2. GeoZentrum Nordbayern, Universität Erlangen-Nürnberg, Schlossgarten 5a, D-91054 Erlangen, Germany;3. The Seventh Geological Brigade of Xinjiang Bureau of Geology and Mineral Resources, Wusu 833000, China |
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| Abstract: | Low-temperature and high-pressure eclogites with an oceanic affinity in the western part of the Dabie orogen have been investigated with combined Lu–Hf and U–Pb geochronology. These eclogites formed over a range of temperatures (482–565 °C and 1.9–2.2 GPa). Three eclogites, which were sampled from the Gaoqiao country, yielded Lu–Hf ages of 240.7 ± 1.2 Ma, 243.3 ± 4.1 Ma and 238.3 ± 1.2 Ma, with a corresponding lower-intercept U–Pb zircon age of 232 ± 26 Ma. Despite the well-preserved prograde major- and trace-element zoning in garnets, these Lu–Hf ages mostly reflect the high-pressure eclogite-facies metamorphism instead of representing the early phase of garnet growth due to the occurrence of omphacite inclusions from core to rim and the shell effect. An upper-intercept zircon U–Pb age of 765 ± 24 Ma is defined for the Gaoqiao eclogite, which is consistent with the weighted-mean age of 768 ± 21 Ma for the country gneiss. However, the gneiss has not been subjected to successive high-pressure metamorphism. The new Triassic ages are likely an estimate of the involvement of oceanic fragments in the continental subduction. |
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