Geochemical constraints on the origin of the Hegenshan Ophiolite,Inner Mongolia,China |
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| Institution: | 1. State Key Laboratory of Coal Mine Disaster Dynamics and Control, School of Resources and Safety Engineering, Chongqing University, Chongqing 400044, China;2. The Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, China;3. Key Laboratory of Geographical Processes and Ecological Security in Changbai Mountains, Ministry of Education, School of Geographical Sciences, Northeast Normal University, Changchun 130024, China;1. Geology Department, Faculty of Science, Zagazig University, Zagazig, Egypt;2. Geology Department, Faculty of Science, Minia University, 61519 Minia, Egypt;1. School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China;3. Center for Advanced Research on the Mantle (CARMA), Chinese Academy of Geological Sciences, Beijing 100037, China;4. Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China;5. Department of Petrology and Mineralogy, Institute of Geology and Paleontology, Havana, Cuba;6. Beijing Research Institute of Uranium Geology, Beijing 100037, China;7. High Mining Metallurgic Institute of Moa \"Dr. Antonio Nunez Jimenez\" (ISMMM), Moa, 83310, Cuba;8. Geology Department, Faculty of Science, Tanta University, Tanta 31527, Egypt;1. CARMA, State Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;2. Department of Geology and Environmental Earth Science, Miami University, Oxford, OH 45056, USA;3. Institute of Geology, Komi Scientific Center, Ural Division, Russian Academy of Sciences, Pervomaiskayaul. 54, Syktyvkar, 167982 Komi Republic, Russia;4. Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, D14473 Potsdam, Germany;5. CMCA, The University of Western Australia, Crawley, WA 6009, Australia |
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| Abstract: | The Hegenshan ophiolite in Inner Mongolia is a remnant of oceanic lithosphere of probable Devonian age. The ophiolite consists of several blocks composed chiefly of serpentinized ultramafic rocks with lesser amounts of troctolite and gabbro, and sparse lavas and dikes. The ultramafic rocks consist chiefly of depleted harzburgite and minor dunite and are interpreted as mantle tectonites. In the Hegenshan block dunite is relatively abundant and is typically associated with podiform chromitite. Both the chromite ore and the residual chromites in this body are relatively aluminous with average Cr numbers of 44–54. A few small chromite bodies and some of the residual chromites have much higher Cr numbers (72–76). Several blocks have well-layered cumulate sequences of gabbro and troctolite. Sheeted dikes are absent but small mafic dikes are common in some of the ultramafic sections. Most of the mafic dikes have flat chondrite-normalized REE patterns and are strongly depleted in incompatible elements, similar to depleted tholeiites from immature island arcs. The basaltic lavas of the Hegenshan ophiolite have two distinctly different chemical signatures—one similar to the mafic dikes and one similar to ocean island basalts. The entire complex was probably formed within an island arc–marginal basin system that was later accreted to the southern margin of the Siberian Altaids. |
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