Mesoproterozoic geomagnetic reversal asymmetry in light of new paleomagnetic and geochronological data for the Häme dyke swarm, Finland: Implications for the Nuna supercontinent

Abstract

Baltica represents one of the key continents of the Mesoproterozoic supercontinent Nuna forming the core of it together with Laurentia and Siberia. This study presents new geochronological and paleomagnetic data obtained for Häme diabase dyke swarm in southern Finland. New U-Pb (baddeleyite) ages 1642 ± 2 Ma and 1647 ± 14 Ma for two reversely magnetized dykes are acquired. Demagnetization revealed a dual polarity remanent magnetization direction carried by magnetite. The combined normal (N) and reversed (R) polarity direction for 11 dykes (=sites) is D = 355.6°, I =-09.1° (k = 8.6 and α95 = 16.6°) yielding a paleomagnetic pole at 23.6°N, 209.8°E (K = 10.6 and A95 = 14.7°) with Van der Voo value Q = 7. N and R magnetized units for the Häme dyke swarm show asymmetry in declination values, probably caused by an age difference between the dykes. The Geocentric Axial Dipole (GAD) model indicates that all geomagnetic reversals should be symmetric (in inclination), yet it has been noted that this is not always the case (e.g. 1.57 Ga Satakunta and Åland dykes in Baltica). By analyzing global dual polarity paleomagnetic data we show that the GAD model is a valid assumption at 1.7-1.4 Ga and that the asymmetry between some 2 normal and reversed polarities in global dual-polarity data sets appears randomly over time, and does not follow a global trend. Further, we show that in the case of Åland and Satakunta dykes an unremoved secondary magnetization component could explain the obtained asymmetry. GAD assumption is used to reconstruct the core of Nuna on equatorial latitudes using new data for Häme dykes. Paleomagnetic evidence suggest that maximum assembly of Nuna occurred at 1.5 Ga and the dispersal of the core is proposed to be associated with coeval 1.38-1.27 Ga magmatism in its core continents.

The long life of SAMBA connection in Columbia: A paleomagnetic study of the 1535 Ma Mucajaí Complex, northern Amazonian Craton, Brazil

“…These paleomagnetic poles define an apparent polar wander (APW) path for Baltica between 1780 Ma and 1430 Ma, as also suggested by Salminen et al (2017) including a quasi-static position of Baltica between 1780 Ma and 1700 Ma (Elming et al, 2019). Paleomagnetic poles from Amazonia and Laurentia for this time interval (Fig.…”

“…A combined mean pole was calculated for these four poles (pole BA1 in Table 2) Table 2) as a key pole representing Baltica at 1700 Ma. A key pole (BA3 in Table 2) was also obtained for the 1642 ± 2 Ma Häme diabase dykes (Salminen et al, 2017) with a maximum quality factor Q=7 (Van der Voo, 1990).…”

“…The Baltica-Laurentia link has received considerable support from several paleomagnetic data sets, although the exact position of Baltica relative to Laurentia has various options (Buchan et al, 2000;Salminen and Pesonen, 2007;Evans and Pisarevsky, 2008;Hamilton and Buchan, 2010;Lubnina et al, 2010;Pisarevsky and Bylund, 2010;Salminen et al, 2009Salminen et al, , 2014Salminen et al, , 2016aSalminen et al, , 2016bSalminen et al, , 2017. The Baltica-Laurentia link was successfully tested at several times between 1830 and 1270 Ma, suggesting a longevity connection between these continents (e.g., Buchan et al, 2000;Pesonen et al, 2012;Cawood and Pisarevsky, 2017).…”

Revised stratigraphic framework for the lower Anti-Atlas Supergroup based on U–Pb geochronology of magmatic and detrital zircons (Zenaga and Bou Azzer-El Graara inliers, Anti-Atlas Belt, Morocco)

“…Corresponding magmatism on Baltica includes the ca. 1.64 Ga NW-trending dyke swarms of Häme, Sipoo, and Suomenniemi and the related rapakivi granite complexes exposed in the Svecofennian Domain of the Fennoscandian Shield in southeast Finland (Vaasjoki et al, 1991;Salminen et al, 2017). The most extensive of these dyke swarms is the 1642 ± 2 Ma Häme diabase dyke swarm (U-Pb ID-TIMS baddelleyite age; Salminen et al, 2017).…”

Probing the Precambrian Geodynamo: Analysis of the Geomagnetic Field Behavior and Calibration of Pseudo-Thellier Paleointensity Method for Mesoproterozoic Rocks

“…The GAD geometry of time-averaged field is reliably established for at least 500-600 millions of years. Furthermore, analyses of paleoclimatological or paleogeographical indicators (e.g., Kent and Smethurst, 1998;Evans, 2006), paleosecular variation (Smirnov et al, 2011), and the zonal harmonics of the geomagnetic field (Veikkolainen et al, 2014;Salminen et al, 2017) indicate that the time-averaged field probably has had the GAD geometry since the Neoarchean. However, the amount and spatiotemporal distribution of the paleomagnetic directional data to date remain insufficient to make a final decisive conclusion for the Precambrian field geometry.…”