High-Field Strength Element Geochemistry of Mafic Intrusive Rocks from the Bhagirathi and Yamuna Valleys,Garhwal Himalaya,India |
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| Institution: | 1. Department of Geology, Banaras Hindu University, Varanasi — 221 005, India;2. Pan India Consultants Pvt. Ltd., 105 Phase IV, Udyog Vihar, Gurgaon — 122 015, India;1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. Department of Earth Sciences, Carleton University, Ottawa, ON K1S 5B6, Canada;3. School of Earth and Space Sciences, Peking University, Beijing 100871, China;4. Department of Geology, Lund University, Sölvegatan 12, 223 62 Lund, Sweden;5. Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China;6. Department of Earth Sciences, University of Toronto, Toronto, ON M5S 3B1, Canada;7. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;8. Centre for Exploration Targeting, School of Earth and Environment, The University of Western Australia, Crawley, WA 6009, Australia;9. Space Research Centre, Polish Academy of Sciences, ul. Bartycka 18A, Warsaw, Poland;10. Department of Applied Geology, Curtin University, GPO Box U1987, Bentley, WA 6845, Australia;11. Institute of Science, Banaras Hindu University, Varanasi 221 005, India;12. Center for Global Tectonics, College of Earth Sciences, China University of Geosciences, Wuhan 430074, China;1. London Geochemistry and Isotope Centre (LOGIC), Institute of Earth and Planetary Sciences, University College London and Birkbeck, University of London, Gower Street, London WC1E 6BT, UK;2. Earth Surface Geochemistry, Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Telegraphenberg, 14473 Potsdam, Germany;3. Department of Geoscience, Swedish Museum of Natural History, 10405 Stockholm, Sweden;4. Department of Earth Sciences, Oxford University, South Parks Road, Oxford OX1 3AN, UK;1. Institute of Surface-Earth System Sciences, Tianjin University, Tianjin 300072, China;2. Institute of Geological Sciences, Freie Universität Berlin, Malteser Straße 74-100, 12249 Berlin, Germany;3. State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;4. State Key Laboratory of Marine Geology, School of Ocean and Earth Science, Tongji University, Shanghai, China;1. Laboratoire de Géochimie et Cosmochimie, Institut de Physique du Globe de Paris (IPGP), UMR 7154 CNRS, Université Paris Diderot, 1 rue Jussieu, 75238 Paris, France;2. GEOTOP, Université du Québec à Montréal, Montréal, Québec H3C 3P8, Canada;3. Institut Universitaire de France, France;4. GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany;5. Laboratoire de Géochimie des Isotopes Stables, Institut de Physique du Globe de Paris (IPGP), UMR 7154 CNRS, Université Paris Diderot, 1 rue Jussieu, 75238 Paris, France;6. Woods Hole Oceanographic Institution, Department of Marine Chemistry and Geochemistry, 360 Woods Hole Road, Woods Hole, MA 02543, USA;7. Department of Geography, Durham University, Science Laboratories, South Road, Durham, DH1 3LE, UK;8. Centre de Recherches Pétrographiques et Géochimiques (CRPG-CNRS), 15 rue Notre Dame des Pauvres, 54501 Vandoeuvre les Nancy, France;1. School of Earth Science and Resources, Chang''an University, Xi''an 710054, China;2. Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China;3. Department of Earth, Marine and Environmental Sciences, University of North Carolina, Chapel Hill, NC 27599-3315, USA;4. School of Resource and Environment, Henan Polytechnic University, Jiaozuo, China;5. State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China |
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| Abstract: | Incompatible high-field strength element geochemistry divides mafic intrusive rocks of Garhwal Himalaya, exposed in the Bhagirathi and Yamuna valleys, into two distinct types, viz. older Garhwal Mafic Intrusive Rocks (GMIR1) and younger Garhwal Mafic Intrusive Rocks (GMIR2). GMIR1 is mainly associated with the Central Crystallines, whereas, GMIR2 belongs to the Garhwal Group. They outcrop close to the Main Central Thrust (MCT) Zone and extend in a NW-SE direction, following the strike direction. Both types are metamorphosed to amphibolite facies and classified as sub-alkaline, high-Fe tholeiitic basalts. They are enriched in large-ion lithophile and high-field strength elements relative to a primitive mantle source. GMIR2 has higher concentrations of incompatible high-field strength elements than the GMIR1. Further, on multi-element spidergrams, GMIR1 samples do not show any elemental anomaly but GMIR2 samples show distinct negative Nb and Sr anomalies. GMIR1 multi-element and rare-earth element trends are similar to N-MORB, whereas, GMIR2 follows trends observed in the within plate basalts (continental flood basalts type). Discrimination diagrams, based on incompatible trace elements, corroborate the N-MORB nature of GMIR1 and CFB (WPB) nature of GMIR2. Geochemical modeling indicates that these mafic intrusive rocks were derived by close-system fractional crystallization of depleted (for GMIR1) to variably enriched parental basalts (for GMIR2). Probably these two contrasting mafic rock types have been juxtaposed during the Himalayan orogeny. Proterozoic mafic rocks of similar geochemical characteristics have been reported from different parts of the northern Indian lithosphere. Observed composition suggests its genetic association with the sub-continental lithosphere rather than effect of crustal contamination. |
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