Parental magma of the Skaergaard intrusion: constraints from melt inclusions in primitive troctolite blocks and FG-1 dykes |
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Authors: | Jakob K. Jakobsen Christian Tegner C. Kent Brooks Adam J. R. Kent Charles E. Lesher Troels F. D. Nielsen Michael Wiedenbeck |
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Affiliation: | 1.Department of Earth Sciences,University of Aarhus,Aarhus C,Denmark;2.Nordic Volcanological Centre, Institute of Earth Sciences,University of Iceland,Reykjavik,Iceland;3.Geological Museum,Copenhagen K,Denmark;4.Department of Geosciences,Oregon State University,Corvallis,USA;5.Department of Geology,University of California, Davis,Davis,USA;6.Geological Survey of Denmark and Greenland,Copenhagen K,Denmark;7.Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum,Potsdam,Germany |
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Abstract: | Troctolite blocks with compositions akin to the Hidden Zone are exposed in a tholeiitic dyke cutting across the Skaergaard intrusion, East Greenland. Plagioclase in these blocks contains finely crystallised melt inclusions that we have homogenised to constrain the parental magma to 47.4–49.0 wt.% SiO2, 13.4–14.9 wt.% Al2O3 and 10.7–14.1 wt.% FeOT. These compositions are lower in FeOT and higher in SiO2 than previous estimates and have distinct La/SmN and Dy/YbN ratios that link them to the lowermost volcanic succession (Milne Land Formation) of the regional East Greenland flood basalt province. New major- and trace element compositions for the FG-1 dyke swarm, previously taken to represent Skaergaard magmas, overlap with the entire range of the regional flood basalt succession and do not form a coherent suite of Skaergaard like melts. These dykes are therefore re-interpreted as feeder dykes throughout the main phase of flood basalt volcanism. |
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