The ~1.85?Ga carbonatite in north China and its implications on the evolution of the Columbia supercontinent |
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| Institution: | 1. School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing 100083, PR China;2. U.S. Geological Survey, Denver Federal Center, Denver, CO 80225, United States of America;3. CODES ARC Centre of Excellence in Ore Deposits, University of Tasmania, Hobart, TAS 7001, Australia;4. Chifeng Chaihulanzi Gold Mining Co. Ltd of Shandong Gold Group, Chifeng 024000, PR China;1. Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China;2. Key Laboratory of Deep-Earth Dynamics of the Ministry of Land and Resources, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;3. Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China;4. Key Laboratory of Submarine Geosciences and Prospecting Technique, MOE and College of Marine Geosciences, Ocean University of China, Qingdao 266100, China;1. Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China;2. Department of Geology and Pedology, Mendel University, Brno, Czech Republic;3. Department of Geological Sciences, University Of Manitoba, Manitoba, Canada;4. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;1. University of Notre Dame, Department of Civil and Environmental Engineering and Earth Sciences, South Bend, IN 46556, USA;2. Munzur University, Department of Geological Engineering, 62000 Tunceli, Turkey;3. State Key Laboratory of Geological Processes and Mineral Resources, Collaborative Innovation Center for Exploration of Strategic Mineral Resources, China University of Geosciences, Wuhan 430074, China;1. Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China;2. Department of Geology and Pedology, Mendel University in Brno, Brno 61300, Czech Republic;3. Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba, R3T 2 N2, Canada;4. Central European Institute of Technology, Brno University of Technology, Brno 61200, Czech Republic;5. State Key Laboratory for Continental Dynamics and Early Life Institute, Department of Geology, Northwest University, Xi''an, 710069, China;6. Xi''an Institute of Geology and Mineral Resources, Xi''an 710054, China |
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| Abstract: | Mantle-derived carbonatites provide a unique window in the understanding of mantle characteristics and dynamics, as well as insight into the assembly and breakup of supercontinents. As a petrological indicator of extensional tectonic regimes, Archean/Proterozoic carbonatites provide important constraints on the timing of the breakup of ancient supercontinents. The majority of the carbonatites reported worldwide are Phanerozoic, in part because of the difficulty in recognizing Archean/Proterozoic carbonatites, which are characterized by strong foliation and recrystallization, and share broad petrologic similarities with metamorphosed sedimentary lithologies. Here, we report the recognition of a ~1.85 Ga carbonatite in Chaihulanzi area of Chifeng in north China based on systematic geological, petrological, geochemical, and baddeleyite U-Pb geochronological results. The carbonatite occurs as dikes or sills emplaced in Archean metasedimentary rocks and underwent intense deformation. Petrological and SEM/EDS results show that calcite and dolomite are the dominant carbonate minerals along with minor and varied amounts of Mg-rich mafic minerals, including forsterite (with Fo > 98), phlogopite, diopside, and an accessory amount of apatite, baddeleyite, spinel, monazite, and ilmenite. The relatively high silica content together with the non-arc and OIB-like trace element signatures of the carbonatite indicates a hot mantle plume as the likely magma source. The depleted Nd isotopic signatures suggest that plume upwelling might be triggered by the accumulation of recycled crust in the deep mantle. As a part of the global-scale Columbia supercontinent, the Proterozoic tectonic evolution of the North China Craton (NCC) provides important insights into the geodynamics governing amalgamation and fragmentation of the supercontinent. The Paleo-Mesoproterozoic boundary is the key point of tectonic transition from compressional to extensional settings in the NCC. The newly identified ~1.85 Ga carbonatite provides a direct link between the long-lasting supercontinental breakup and plume activity, which might be sourced from the “slab graveyard,” continental crustal slabs subducted into asthenosphere, beneath the supercontinent. The carbonatite provides a precise constraint of the initiation of the continental breakup at ~1.85 Ga. |
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