PALEOMAGNETIC STUDY OF THE MESOPROTEROZOIC SATAKUNTA DYKE SWARM, FINLAND, WITH IMPLICATIONS FOR A NORTHERN EUROPE – NORTH AMERICA (NENA) CONNECTION WITHIN NUNA SUPERCONTINENT

Johanna Salminen1, Satu Mertanen2 and David Evans3

1. Department of Physics, Division of Geophysics and Astronomy, University of Helsinki, Finland 2. Geological Survey of Finland, South Finland Unit, Espoo, Finland 3. Department of Geology and Geophysics, Yale University, New Haven, USA

Paleoproterozoic supercontinent Nuna (Columbia, Hudsonland) has been suggested by several studies. Many recent reconstructions of this supercontinent are based on assumption that the core of Nuna was formed by the united Baltica and Laurentia cratons forming the NENA (Northern Europe – North America) configuration that lasted from 1.8 Ga to at least 1.26 Ga. However, recent 1.6 Ga data from Greenland appear to challenge this fit (Halls et al., 2011). Our new data from the Mesoproterozoic (1565 Ma) diabase dyke swarm in Satakunta, western Finland, provides new paleomagnetic evidence to test the NENA configuration. From the Satakunta dykes a dual-polarity, high-stability remanence component was obtained and it was confirmed to be primary by several baked contact tests. A suite of rock-magnetic analyses demonstrates that pseudo-single domain magnetite is the remanence carrier. The combined mean remanence direction for both polarities is D = 8.3°, I = 6.5° ( 95 = 5.9°), yielding a new key paleomagnetic pole for Baltica at 32.7°N, 188.7°E (A95 = 4.2°). This pole fulfills six out of seven van der Voo factors. Based on the reconstruction by using the new Satakunta pole and the nearly coeval (1592 Ma) Western Channel Diabase pole from Laurentia (Irving, 1972; Hamilton and Buchan, 2010), the NENA fit existed at 1.57-1.59 Ga. Consequently, coeval paleomagnetic data coupled with correlations of geochronology and basement geology of Baltica and Laurentia validates the NENA fit at 1.77-1.75 Ga, 1.59-1.57 Ga, 1.46 Ga, and 1.27 Ga. Using the same NENA reconstruction, the dual-polarity 1.63 Ga paleomagnetic poles from Greenland (Melville Bugt, Halls et al., 2011) and Finland (Sipoo, Mertanen and Pesonen, 1995) are offset by about 30°. However, when using the whole range of the fairly scattered data from individual sites, the NENA fit can be allowed. In Sipoo dykes, as well as in several other similar aged formations in Fennoscandia, the reversed polarity data are more scattered than normal polarity data, possibly due to transition of the Earth’s magnetic field during remanence acquisition.

References

Halls, H. C., Hamilton, M., Denyszyn, S. W., 2011. The Melville Bugt dyke swarm of Greenland: A connection to the 1.5 - 1.6 Ga Fennoscandian rapakivi granite province? In: Srivastava (ed.) Dyke Swarms: keys for Geodynamic Interpretation, 509-535. doi 10.1007/987-3-642-12496- 9_27.

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Hamilton, M. and Buchan, K., 2010. U–Pb geochronology of the Western Channel Diabase, northwestern Laurentia: Implications for a large 1.59 Ga magmatic province, Laurentia's APWP and paleocontinental reconstructions of Laurentia, Baltica and Gawler craton of southern Australia. Prec. Res. 183, 464-473. Irving, E., Donaldson, J.A. and Park, J.K., 1972. Paleomagnetism of the Western Channel Diabase and associated rocks, Northwest Territories. Can. J. Earth Sci. 9, 960–971. Mertanen, S., Pesonen, L. J., 1995. Paleomagnetic and rock magnetic investigations of the Sipoo Subjotnian quartz porphyry and diabase dykes, southern Fennoscandia. Phys. Earth Planet. Int. 88, 145-175.

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