A palaeomagnetic analysis of rapakivi intrusions and related dykes in the Fennoscandian Shield |
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| Affiliation: | 1. Department of Earth Sciences, University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 5B7, Canada;2. Institute for Earth and Space Exploration, University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 5B7, Canada;3. Natural History Museum Vienna, Burgring 7, A-1010 Vienna, Austria;4. Institute of Geological Sciences, Polish Academy of Sciences, Podwale 75, 50-449 Wroclaw, Poland;5. School of Geographical and Earth Sciences, University of Glasgow, Molema Building, Lilybank Gardens, Glasgow G12 8QQ, UK;6. School of Earth and Planetary Science, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia;7. Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada;8. Canada Aviation and Space Museum, Ingenium, 11 Aviation Parkway, Ottawa, Ontario, Canada;9. Centre for Terrestrial and Planetary Exploration, University of Winnipeg, Winnipeg, Manitoba R3B 2E9, Canada;10. Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, 2101 NASA Road One, Houston, TX 77058, USA |
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| Abstract: | In the Fennoscandian Shield (Baltica) there are seven major rapakivi plutons and fifteen minor ones ranging in age from ca 1.66 to 1.50 Ga. These plutons are distributed in a broad WNW zone and if the most eastern pluton is excluded there is a westward trend of decreasing age of the intrusions. A palaeomagnetic study has been performed on 4 minor plutons (Rödö, Mårdsjö, Norsjö and Mullnäset) and associated dykes in central Sweden. The results were combined with palaeomagnetic data from other rapakivi complexes in Fennoscandia in order to test if a stationary hot spot may be the origin of these anorogenic intrusions. Plotting the pole positions of this study together with poles of other complexes, poles calculated from rapakivi rocks and related dykes in Finland are located at somewhat lower latitudes and more eastern longitudes than poles of corresponding rocks in Sweden, probably reflecting an APW related to the general age differences between the plutons. The palaeolatitudes for the Fennoscandian Shield at the time of the rapakivi intrusions are restricted to a latitudinal range between ca 16° south and 27° north and there is a weak trend of increasing palaeolatitude with decreasing age of the rocks. A trend of gradually changing palaeolatitudinal positions has also been observed for the intrusion of Proterozoic anorthosite-rapakivi plutons in the Ukranian Shield. Such differences in palaeolatitudes is not expected in case of a single stationary hot spot being the source of the rapakivi intrusions, as the rock then should carry a magnetization reflecting the same latitudinal position. |
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