Seamounts off the West Antarctic margin: A case for non-hotspot driven intraplate volcanism |
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| Institution: | 1. GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1-3, D-24148 Kiel, Germany;2. Alfred-Wegener-Institute for Polar and Marine Research, Postfach 120161, D-27515 Bremerhaven, Germany;3. University of Bremen, Postfach 330440, D-28334 Bremen, Germany;1. Institute of Geophysics, Polish Academy of Sciences, Ks. Janusza 64, 01-452 Warsaw, Poland;2. Institute of Geophysics, Faculty of Physics, University of Warsaw, Pasteura 7, 02-093 Warsaw, Poland;1. Dept. of Earth and Planetary Sciences, Macquarie University, Sydney, Australia;2. Laboratoire de Géologie de Lyon, Ecole Normale Supérieure de Lyon, Université Claude Bernard Lyon 1, and CNRS, 69007 Lyon, France;1. Dipartimento di Scienze della Terra, Sapienza Università di Roma, P.le Aldo Moro, 5, 00185 Rome, Italy;2. Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56126 Pisa, Italy;1. Dept. Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK;2. British Antarctic Survey (BAS), High Cross, Madingley Road, Cambridge CB3 0ET, UK;3. Instituto Andaluz de Ciencias de la Tierra (IACT), CSIC/Univ. Granada, Campus de Fuentenueva, s/n, 18002 Granada, Spain |
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| Abstract: | New radiometric age and geochemical data of volcanic rocks from the guyot-type Marie Byrd Seamounts (MBS) and the De Gerlache Seamounts and Peter I Island (Amundsen Sea) are presented. 40Ar/39Ar ages of the shield phase of three MBS are Early Cenozoic (65 to 56 Ma) and indicate formation well after creation of the Pacific–Antarctic Ridge. A Pliocene age (3.0 Ma) documents a younger phase of volcanism at one MBS and a Pleistocene age (1.8 Ma) for the submarine base of Peter I Island. Together with published data, the new age data imply that Cenozoic intraplate magmatism occurred at distinct time intervals in spatially confined areas of the Amundsen Sea, excluding an origin through a fixed mantle plume. Peter I Island appears strongly influenced by an EMII type mantle component that may reflect shallow mantle recycling of a continental raft during the final breakup of Gondwana. By contrast the Sr–Nd–Pb–Hf isotopic compositions of the MBS display a strong affinity to a HIMU-type mantle source. On a regional scale the isotopic signatures overlap with those from volcanics related to the West Antarctic Rift System, and Cretaceous intraplate volcanics in and off New Zealand. We propose reactivation of the HIMU material, initially accreted to the base of continental lithosphere during the pre-rifting stage of Marie Byrd Land/Zealandia to explain intraplate volcanism in the Amundsen Sea in the absence of a long-lived hotspot. We propose continental insulation flow as the most plausible mechanism to transfer the sub-continental accreted plume material into the shallow oceanic mantle. Crustal extension at the southern boundary of the Bellingshausen Plate from about 74 to 62 Ma may have triggered adiabatic rise of the HIMU material from the base of Marie Byrd Land to form the MBS. The De Gerlache Seamounts are most likely related to a preserved zone of lithospheric weakness underneath the De Gerlache Gravity Anomaly. |
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