Geochronology and geochemistry of late Carboniferous volcanic rocks from northern Inner Mongolia,North China: Petrogenesis and tectonic implications |
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| Institution: | 1. School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. Center for Global Tectonics, China University of Geosciences, Wuhan 430074 China;3. Institute of Geological Survey, China University of Geosciences, Wuhan 430074, China;4. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. University of Chinese Academy of Sciences, Beijing 100039, China;1. College of Earth Sciences, Jilin University, Changchun 130061, PR China;2. College of Marine Geosciences, Ocean University of China, Qingdao 266003, PR China;3. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, PR China;4. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, PR China;1. College of Earth Sciences, Jilin University, Changchun 130061, China;2. Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong;3. The Laboratory Centre of Institute of Earth Sciences, China University of Geosciences, Beijing 100083, China |
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| Abstract: | Zircon U–Pb ages, geochemical and Sr–Nd isotopic data are presented for the late Carboniferous Baoligaomiao Formation (BG Fm.) and Delewula Formation (DW Fm.) volcanic rocks, widely distributed in northern Inner Mongolia, in the northern part of the Xing'an–Mongolia Orogenic Belt (XMOB). The BG Fm. rocks mainly consist of basaltic andesites and andesites while the DW Fm. rocks include dacites, trachytes, rhyolites, pyroclastic rocks and minor andesites. New LA-ICPMS zircon U–Pb analyses constrain their eruption to late Carboniferous (317–322 Ma and 300–310 Ma, respectively). The BG Fm. volcanic rocks are characterized by enriched large ion lithophile elements (LILE) and depleted high field strength elements (HFSE), with initial 87Sr/86Sr ratios of 0.70854–0.70869 and negative εNd(t) (? 2.1 to ? 2.4) values. They have low La/Ba (0.03–0.05), high La/Nb (2.05–3.70) ratios and variable Ba/Th (59.5–211) ratios. Such features suggest that they are derived from melting of heterogeneous sources including a metasomatized mantle wedge and Precambrian crustal material. The DW Fm. volcanic rocks are more depleted in HFSE with significant Nb, Ta, P, Ti anomalies. They have high initial 87Sr/86Sr ratios (0.72037–0.72234) and strong negative εNd(t) (? 11 to ? 11.6) values which indicate those igneous rocks were mainly derived from reworking of the Paleoproterozoic crust. The late Carboniferous volcanic rocks have geochemical characteristics similar to those of the continental arc rocks which indicate the northward subduction of the Paleo Asian Ocean may have continued to the late Carboniferous. The volcanic association of this study together with the early Permian post-collisional magmatic rocks suggests that a tectonic transition from subduction-related continental margin arc volcanism to post-collisional magmatism occurred in the northern XMOB between the late Carboniferous and the early Permian. |
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