Combined Sr,Nd, Pb and Li isotope geochemistry of alkaline lavas from northern James Ross Island (Antarctic Peninsula) and implications for back-arc magma formation |
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| Authors: | J Ko?ler T Magna B Ml?och P Mixa D Nývlt FV Holub |
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| Institution: | 1. Research School of Earth Sciences, The Australian National University, 2601 Acton, ACT, Australia;2. School of Earth, Atmosphere and Environment, Monash University, 3800 Clayton, VIC, Australia;3. Institut für Geowissenschaften, Goethe Universität Frankfurt, 60438 Frankfurt am Main, Germany;1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, PO Box 9825, Beijing 100029, China;2. Department of Earth and Planetary Sciences, Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS) and GEMOC, Macquarie University, NSW, 2109, Australia;3. CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;1. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi''an, 710069, China;2. Department of Geology and Geophysics, School of Physical Sciences, The University of Adelaide, South Australia 5005, Australia;1. Instituto Andaluz de Ciencias de la Tierra, Campus de Fuentenueva, CSIC-UGR, Granada, Spain;2. Instituto Geológico y Minero de España, Madrid, Spain;3. Departamento de Geodinámica, Universidad de Granada, Granada, Spain;4. Dept. Earth Sciences, Royal Holloway Univ. London, Egham, UK;5. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Trieste, Italy;6. P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia |
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| Abstract: | We present a comprehensive geochemical data set for a suite of back-arc alkaline volcanic rocks from James Ross Island Volcanic Group (JRIVG), Antarctic Peninsula. The elemental and isotopic (Sr, Nd, Pb and Li) composition of these Cenozoic basalts emplaced east of the Antarctic Peninsula is different from the compositions of the fore-arc alkaline volcanic rocks in Southern Shetlands and nearby Bransfield Strait. The variability in elemental and isotopic composition is not consistent with the JRIVG derivation from a single mantle source but rather it suggests that the magma was mainly derived from a depleted mantle with subordinate OIB-like enriched mantle component (EM II). The isotopic data are consistent with mantle melting during extension and possible roll-back of the subducted lithosphere of the Antarctic plate. Magma contamination by Triassic–Early Tertiary clastic sediments deposited in the back-arc basin was only localized and affected Li isotopic composition in two of the samples, while most of the basalts show very little variation in δ7Li values, as anticipated for “mantle-driven” Li isotopic composition. These variations are difficult to resolve with radiogenic isotope systematics but Li isotopes may prove sensitive in tracking complex geochemical processes acting through the oceanic crust pile, including hydrothermal leaching and seawater equilibration. |
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