Detrital zircon provenance constraints on the final closure of the middle segment of the Paleo-Asian Ocean |
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| Institution: | 1. Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China;2. Department of Geology, Northwest University, Xi''an 710069, China;3. Department of Geology and Planetary Science, University of Pittsburgh, 4107 O''Hara Street, Pittsburgh, PA 15260-3332, USA;4. Institute of Earth Sciences, Academia Sinica, Taipei 11529, Taiwan;1. Institute for Peat and Mire Research, School of Geographical Sciences, Northeast Normal University, Changchun 130024, China;2. The Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, China;3. Research School of Earth Sciences, Australian National University, Mills Road, Canberra, ACT 0200, Australia;1. Key Laboratory of Computational Geodynamics, University of Chinese Academy of Sciences, Beijing 100049, China;2. Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China;3. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;4. Department of Geology, The University of Leicester, Leicester LE1 7RH, UK;1. Key Laboratory of Computational Geodynamics, University of Chinese Academy of Sciences, Beijing 100049, China;2. Department of Geosciences, National Taiwan University, Taipei 10617, Taiwan;3. Institute of Earth Sciences, Academia Sinica, Taipei 11529, Taiwan;4. Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China;5. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. CAS Center for Excellence in Tibetan Plateau Earth Sciences, China;3. Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China;4. Department of Geology, University of Leicester, Leicester LE1 7RH, UK;5. Department of Earth and Planetary Sciences, Macquarie University, Sydney NSW 2109, Australia |
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| Abstract: | The main site and timing of the final closure of the middle segment of the Paleo-Asian Ocean (PAO) has been an issue of hot debate, which hampers us from better understanding the late-stage tectonic evolution of the Central Asian Orogenic Belt (CAOB). Synthesizing the available geological records for the ophiolitic mélanges in the Beishan Orogenic Belt (BOB), we regard the Liuyuan ophiolitic mélange as the main site of the final closure of the middle segment of the PAO. To determine the final closure time of the middle segment of the PAO, this study mainly applied field-based, systematic zircon U-Pb-Hf isotopic analyses for the Carboniferous and Permian sedimentary successions on the northern and southern sides of the Liuyuan ophiolitic mélange. Our results indicate that the late Carboniferous sedimentary successions north of the Liuyuan mélange consisting mainly of interbedded sandstone and siltstone with minor conglomerate show primarily affinity with a local, single source, i.e. the constituent units of the BOB north of the Liuyuan mélange. They were closely associated with the northward subduction of the middle segment of the PAO. By contrast, the unconformably overlying Permian clastic deposition on both sides of the Liuyuan ophiolitic mélange shows comparable lithology that fines from a thick sequence of conglomerate at the base to thin-bedded turbidite sequences up section. These Permian units were probably deposited in a progressively deepening basin within an extensional post-collision regime after the disappearance of the middle segment of the PAO. All the <274–261 Ma sandstones on both sides of the Liuyuan ophiolitic mélange were derived from commingling source regions on both sides of the Liuyuan mélange, as supported by comparable, diagnostic ages and εHf(t) values between the studied detrital zircons and coeval magmatic zircons from the BOB and north Tarim. Such a marked transition from a single, local provenance in the late Carboniferous to commingling provenances at ca. 274–261 Ma indicates the final closure of the middle segment of the PAO prior to the end of the early Permian. In conjunction with available data for the eastern and western segments of the PAO, we establish the eastward-younging, scissor-like closure for the whole PAO during mid Carboniferous to Early Triassic time. |
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