The Zhaheba ophiolite complex in Eastern Junggar (NW China): Long lived supra-subduction zone ocean crust formation and its implications for the tectonic evolution in southern Altaids |
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| Institution: | 1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, PR China;2. CAS Center for Excellence in Tibetan Plateau Earth Sciences, PR China;3. Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China;4. Department of Earth and Environmental Sciences, California State University, Fresno, CA 93740, USA;1. Laboratory of Isotope Thermochronology, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;2. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;3. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;4. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;5. Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China;6. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;7. Department of Geology, Northwest University, Xi''an 710069, China;1. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, CAS, Beijing 100029, PR China;2. Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, PR China;3. University of Chinese Academy of Sciences, 100049 Beijing, China;4. United States Geological Survey, Reno, Nevada 89557, United States;5. Institute of Geology and Geophysics, CAS, Beijing 100029, PR China;6. College of Resource and Environment Sciences, Xinjiang University, 830046, PR China;7. School of Geosciences and Resources, China University of Geosciences, Beijing 100083, PR China;8. State Key Laboratory of Geological Processes and Mineral Resources, Science Research Institute, China University of Geosciences, Beijing 100083, PR China;9. Shanxi Center of Geological Survey, Xi''an, Shanxi 710068, PR China;10. Panjin Zhonglu Oil&Gas Technology Services Co. Ltd, Liaoning 124000, PR China;1. The Key Laboratory of Marine Reservoir Evolution and Hydrocarbon Accumulation Mechanism, Ministry of Education, China University of Geosciences, Beijing 100083, China;2. School of Earth Sciences and Resources, China University of Geosciences, Beijing, China;1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. University of Chinese Academy of Sciences, Beijing 10069, China;3. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Northern Taibai Str. 229, Xi''an 710069, China;4. Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China |
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| Abstract: | The composite Zhaheba ophiolite complex, exposed in Eastern Junggar in the Southern Altaids, records an unusually long record of oceanic crust and magmatic arc evolution. The Zhaheba ophiolite complex consists of ultramafic rocks, gabbro, diorite, basalt and chert intruded by diabase dikes and diorite porphyry. These rocks are overlain by a several-km-thick section of tuffaceous rocks, volcaniclastic sedimentary rocks, and intermediate volcanic rocks. The igneous rocks of the ophiolite complex show negative Nb and Ta anomalies and LREE enrichment relative to HREE, suggesting the influence of fluids derived from a subducting oceanic slab. The LA-ICPMS U–Pb age of zircons from gabbro is 495.1 ± 3.5 Ma. Zircon ages from diorite and basalt are 458.3 ± 7.2 Ma and 446.6 ± 6.0 Ma, respectively. The basalt is locally overlain by bedded chert. Diabase dikes and diorite porphyry yield the U–Pb ages of 421.5 ± 4.1 Ma and 423.7 ± 6.5 Ma, respectively. The age of stratigraphically lower part of the overlying volcanic–volcaniclastic section is constrained to be about 410 Ma, the maximum depositional age of the tuffaceous sandstone from U–Pb detrital zircon ages. Late rhyolite at the top of the stratigraphic section yielded a U–Pb zircon age of 280.3 ± 3.7 Ma. The age and stratigraphic relationships for the Zhaheba ophiolite complex and related rocks suggest that the period of ~ 70 Ma of initial supra-subduction magmatism was followed by construction of a mature island arc that spanned an additional 140 Ma. Many other ophiolites in the southern Altaids appear to record similar relationships, and are represented as substrates of oceanic island arcs covered by island arc volcanism in supra-subduction zone. The occurrence of the Zhaheba ophiolite complex with tuffaceous and intermediate to felsic volcanic rocks is different from the rock association of classic Tethyan SSZ ophiolites but similar to some ophiolites in North America. Although the Zhaheba ophiolite belt is flanked by the Dulate arc in the north and Yemaquan arc in the south, it cannot stand a suture between two arcs. It is suggested that Devonian–Carboniferous Dulate arc was built on the late Cambrian–middle Ordovician Zhaheba supra-subduction oceanic crust. The late Carboniferous rocks and early Permian rocks in Dulate arc are interpreted to form in the extensional process within Zhaheba–Dulate arc composite system. |
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