NEW PALEOMAGNETIC RESULTS FROM 1.3 GA MAFIC DYKES OF BORNHOLM (DENMARK) WITH IMPLICATIONS TO BALTICA IN NUNA

A paleomagnetic study on N-NNE striking mafic dykes and 1.45-1.46 Ga (Waight et al., 2012) host gneisses and granodiorites was carried on in the Danish island of Bornholm. Our aim was to fill gap in the paleomagnetic record of Baltica and test further the proposed existence of the NENA (Northern Europe – North America) connection between Baltica and Laurentia.

Stable normal polarity characteristic remanent magnetization (ChRM) direction with NE declination and intermediate upward pointing inclination carried by magnetite was obtained for 27 dykes. Similar reversed polarity ChRM was obtained for the well-dated 1326 ± 10 Ma (Holm et al., 2005) Kelseå dyke. One normal polarity dyke provides a full positive baked contact test, proving the primary remanence for the new Bornholm pole. In addition, ten narrow dykes showed reversed polarity magnetization with ca. 20° higher inclinations than normal polarity dykes. Based on detailed rock magnetic analyses we interpret that difference in inclination values are due to uncleaned hematite component. Our results contradict earlier paleomagnetic results from Bornholm (Abrahamsen and Lewandowski, 1995; Lubnina et al., 2009) and we propose that earlier the common secondary component obtained widely in Fennoscandia (e.g. Bylund, 1985; Bylund and Elming, 1992; Mertanen et al., 2008) was interpreted as primary remanence.

The new high-quality 1.33 Ga pole for Baltica is located between 1.45 Ga and 1.25 Ga high-quality poles of Baltica. When rotated according to the NENA configuration (e.g. Evans and Pisarevsky, 2008), it is located between 1.39 Ga and 1.31 Ga high-quality poles of Laurentia, thus further supporting the juxtaposition of Baltica and Laurentia at 1.33 Ga. Coeval 1.38–1.32 Ga large igneous provinces at Baltica, Laurentia and Siberia (Ernst, 2014) indicate that these continental blocks forming the core of supercontinent Nuna remained still at proximity to each other.