Geochemistry and Origin of Neoproterozoic Granitoids of Meghalaya, Northeast India: Implications for Linkage with Amalgamation of Gondwana Supercontinent |
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| Authors: | Subhasish Ghosh AE Fallick DK Paul PJ Potts |
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| Institution: | aGeochronology and Isotope Geology Division, Geological Survey of India, 15A & B, Kyd Street, Kolkata - 700 016, India;bScottish Universities Environmental Research Centre, East Kilbride, Glasgow G75 OQF, Scotland;cDepartment of Geology, Presidency College, College Street, Kolkata-700073, India;dDepartment of Earth Sciences, The Open University, Milton Keynes MK76AA, U.K. |
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| Abstract: | Many granitic bodies intrude the basement gneisses in Meghalaya Plateau, Northeast India. Rb-Sr whole-rock isotopic ages of the granitoids range from 881 to 479 Ma while the ages of the basement orthogneisses vary from 1714 to 1150 Ma. All the plutons are dominantly metaluminous and show geochemical variation. Oxygen isotopic compositions in the granitoids and gneisses are concordant (d18O: + 5.78% to + 8.70%). However, the gneisses from high-grade terrain have low d18O value of +2.52% to +5.31%. Initial 87Sr/86Sr (ISr) ratios of the plutons vary from 0.70459 to 0.71487 and tend to increase with progressive younging in age. The geochemical characters suggest derivation of the granites from lower crustal source. The fractionated rare earth patterns observed in the granitoids can be obtained by partial melting of gneisses or diorites. Some gneiss samples have experienced interaction with hydrothermal fluids resulting in lowering d18O. The isotopic ages of granite plutonism in Meghalaya are similar to the plutonic and tectonothermal events in other parts of India, southwestern Australia and document final amalgamation events of the Gondwana Supercontinent. |
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| Keywords: | Neoproterozoic granite oxygen isotope petrogenesis Meghalaya Northeast India |
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