Geochemical signature and rock associations of ocean ridge-subduction: Evidence from the Karamaili Paleo-Asian ophiolite in east Junggar,NW China |
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| Institution: | 1. Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China;2. Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Materials in Guangxi & Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, Guilin University of Technology, Guilin 541004, China;3. Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, CAS, Guangzhou 510640, China;4. Scripps Institution of Oceanography, UCSD, La Jolla, CA 92093, USA;1. SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Baiwanzhuang Road 26, Beijing 100037, China;2. Institut für Geowissenschaften, Universität Mainz, D-55099 Mainz, Germany;3. Department of Geosciences, National Taiwan University, P.O. Box 13-318, Taipei 106, Taiwan;4. Department of Geology, University of Leicester, Leicester LE1 7RH, UK;5. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;6. Institute of Geology and Mineral Resources, Mongolian Academy of Sciences, Ulaanbaatar 210351, Mongolia;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. Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China;2. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;3. School of Earth Sciences and Resources, China University of Geosciences Beijing, No. 29 Xueyuan Road, Haidian District, Beijing 100083, China;4. Division of Interdisciplinary Science, Faculty of Science, Kochi University, Akebono-cho, Kochi 780-8520, Japan |
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| Abstract: | Subduction of active spreading ridges most likely occurs throughout Earth's history. Interaction or collision between spreading center and trench, with the active spreading ridge downgoing and shallowly being buried in subduction zone, results in low-pressure but high-temperature near-trench magmatism in the forearc and accretionary prism setting. The Central Asian region, a complex orogenic belt created during the evolution and closure of the Paleo-Asian Ocean (PAO) at ~ 1000–300 Ma, provides an ideal place to study the subduction of PAO spreading ridges beneath ancient continental margins. It had been suggested that the low-pressure and high-temperature mafic and intermediate to felsic magmas from the Karamaili ophiolite (KO) in the NE corner of the Junggar basin (NW China) in Central Asia were likely produced by ridge subduction (Liu et al., 2007). In this paper, we combine our new geochemical data with previous results to show that the geochemical characteristics of the bulk of KO mafic rocks range from arc basalt-like to mid-ocean ridge basalt-like and ocean island basalt-like. Their trace element patterns range from depleted to enriched in highly incompatible elements, but depleted in Nb and Ta, indicating a subduction-influenced origin. The KO intermediate to felsic rocks are calc-alkaline and boninitic in composition and have trace element signatures similar to the associated mafic rocks. The low Nb/Ta ratios of some of the mafic rocks and boninitic character of some of the intermediate to felsic rocks reflect a highly depleted source, perhaps due to prior backarc magmatism. Major and trace element models indicate complex fractional crystallization histories of parental KO magmas to generate both the mafic and intermediate to felsic rocks, but in general, crystal fractionation occurred at 1000 to 1200 °C and moderate to low (0.5 kbar to 10 kbar) pressure or < 23 km depth. We conclude that the KO was formed in a forearc region of a subduction system that experienced ridge subduction. |
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