Geochemical constraints on Carboniferous volcanic rocks of the Yili Block (Xinjiang,NW China): Implication for the tectonic evolution of Western Tianshan |
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| Institution: | 1. School of Earth Science and Resources, Chang''an University, Xi''an 710054, China;2. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;3. Department of Geology, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario P7B5E1, Canada |
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| Abstract: | The Yili Block is important for understanding the Late Paleozoic geodynamic evolution of Central Asia. It is bounded to the north by the Northern Tianshan Carboniferous flysch and ophiolitic mélange. The center of the Block is dominated by Carboniferous sedimentary rocks with intercalation of volcanic rocks. Petrological and geochemical features of these Carboniferous volcanic rocks show that: (1) they belong to the calc-alkaline series, (2) they display prominent Nb–Ta negative anomalies consistent with subduction-related magmas, and (3) HFSE-based discriminations place these volcanic rocks in the field of continental arcs. The depositional evolution of the sedimentary series shows evidence for Carboniferous sedimentation in a basin instead of rifting as previously proposed. All these evidences, together with the occurrence of contemporaneous turbidites and ophiolitic mélange along the northern boundary of the Yili Block, allow us to infer that the northern border of the Yili Block was a continental active margin during the Carboniferous. The Late Carboniferous southward subduction that finally closed the Late Devonian to Early Carboniferous North Tianshan oceanic basin was followed by Permian–Mesozoic polyphase transcurrent faulting. |
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