A record of ultrahigh temperature metamorphism in the Dabie orogen during Triassic continental collision |
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| Institution: | 1. School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. Institut für Mineralogie und Kristallchemie, Universität Stuttgart, Stuttgart 70174, Germany;1. Department of Earth Sciences, University of Turin, 10125 Turin, Italy;2. Department of Physics and Earth Sciences, University of Ferrara, 44122 Ferrara, Italy;3. Institute of Condensed Matter Chemistry and Technology for the Energy, CNR, Padua, Italy;4. Department of Chemistry, University of Turin, 10125 Turin, Italy;5. \"G. Scansetti\" Interdepartmental Center for Studies on Asbestos and Other Toxic Particulates, Turin, Italy;1. School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China;2. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China;3. Key Laboratory of Tectonics and Petroleum Resources, China University of Geosciences, Ministry of Education, Wuhan 430074, China;4. Tianjin Branch, China Petroleum Logging CO. LTD., Tianjin 300457, China;5. School of Ocean and Earth Science, Tongji University, Shanghai 200092, China;6. Wuxi Research Institute of Petroleum Geology, Petroleum Exploration and Development Research Institute, SINOPEC, Wuxi 214126, China;7. Research Institute of Exploration and Development, Xinjiang Oilfield Company, PetroChina, Urumqi 830013, China;1. Department of Earth and Environmental Sciences, The Earth and Environmental Science System Research Center, Chonbuk National University, Jeonju 561–756, Republic of Korea;2. Geology Division, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, South Korea;3. Divisions of Earth and Environmental Sciences, Korea Basic Science Institute, Ochang 363–883, Republic of Korea;1. Beijing SHRIMP Centre, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, 100037 Beijing, China;2. Department of Geosciences, University of Mainz, D-55099 Mainz, Germany;1. Center for Mineral Resources Science, Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401, USA;2. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;3. Department of Geology, The University of Kansas, 1475 Jayhawk Boulevard, Lawrence, KS 66045, USA |
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| Abstract: | Ultrahigh temperature (UHT) metamorphism is traditionally recognized by the development of characteristic mineral associations in Mg–Al-rich metapelitic rocks. However, recognition of UHT metamorphism in non-supracrustal rocks is more difficult. UHT metamorphic conditions are recorded by a migmatite from the North Dabie Terrane (NDT) of the Dabie orogen, east China. The migmatite is composed of intercalated layers of melanosome and K-feldspar-rich leucosome. Zircon grains in the migmatite have a core–rim structure comprising a metamorphic core and an anatectic rim. The metamorphic cores have low U contents (mainly <657 ppm) and low Th/U ratios (<0.2), and are depleted in heavy rare earth element (HREE). The metamorphic domains yield concordant 206Pb/238U ages ranging from 205.1 ± 4.8 Ma to 248.0 ± 4.1 Ma with a weighted mean of 217.7 ± 4.3 Ma (n = 20, MSWD = 4.2). They contain a granulite-facies inclusion assemblage of garnet + clinopyroxene + plagioclase + quartz + rutile. Conventional geobarometry and Ti-in-zircon thermometry constrain P–T conditions to approximately 11–12 kbar and 900–950 °C, suggesting UHT metamorphism. The discovery of Triassic UHT metamorphism in the Dabie orogen, which was previously best known for ultrahigh pressure metamorphism, provides new insights into the thermal structure and geodynamics of the orogeny during continental collision. The anatectic rims of zircon grains have relatively high U contents and low Th/U ratios (<0.14), and are enriched in HREE. They yield concordant 206Pb/238U ages of 133.6 ± 1.1 Ma to 156.4 ± 2.2 Ma, indicating that anatexis occurred during post-collisional collapse of the Dabie orogen. |
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