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Anomalous strontium and lead isotope signatures in the off-rift Öræfajökull central volcano in south-east Iceland: Evidence for enriched endmember(s) of the Iceland mantle plume? |
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| Authors: | Tore Prestvik Steven Goldberg Haraldur Karlsson Karl Grnvold |
| Institution: | a Department of Geology and Mineral Resources Engineering, Norwegian University of Science and Technology, N-7491, Trondheim, Norway b Department of Geology, University of North Carolina, Chapel Hill, NC 27599-3315, USA c Department of Geosciences, Texas Tech University, Lubbock, Texas 79409, USA d Nordic Volcanological Institute, Grensásvegur 50, IS-108, Reykjavik, Iceland |
| Abstract: | The currently active off-rift central volcano Öræfajökull in south-east Iceland sits unconformably on much older ( 10–12 Ma) and eroded crust. The composition of recent volcanics ranges from basalt to rhyolite, but the series is more sodic alkaline than the common rift zone tholeiitic suites. In this study we present Sr, Nd, Pb and O isotopic data for a suite of Öræfajökull samples. The complete suite shows typical mantle values for oxygen isotopes. The 87Sr/86Sr ratios (average of 15 SAMPLES=0.703702) of the modern Öræfajökull rocks (basalts as well as rhyolites) are much higher than observed so far for any other Icelandic rocks. The 143Nd/144Nd ratios (average=0.512947; n=15) are lower than for rift rocks, but similar to rocks of the off-rift Snæfellsnes volcanic zone. Furthermore, the Öræfajökull rocks are enriched in the 207Pb/204Pb and 208Pb/204Pb isotope ratios compared to Icelandic rift basalts. The enriched nature of the suite indicates that Öræfajökull samples a source component that has characteristics common with EM2 type mantle. Furthermore, it is concluded that the silicic rocks of Öræfajökull formed by fractional crystallization from mafic melts rather than by partial melting of older crust. |
| Keywords: | Author Keywords: rift zones volcanoes stable isotopes radioactive isotopes enrichment Icelandic Plume |
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