Palaeomagnetism of the Salla Diabase Dyke, northeastern Finland, and its implication for the Baltica-Laurentia entity during the Mesoproterozoic

Abstract

New palaeomagnetic and rock magnetic results are presented for the 1122 + 7 Ma Salla Diabase Dyke in NE Finland. A positive baked-contact test proves that the dyke has a primary natural remanent magnetization carried by magnetite. The characteristic remanent magnetization direction (D ¼ 42.28, I ¼ 73.98, k ¼ 75.78, a 95 ¼ 4.88) of 13 sites along the large single dyke provides a virtual geomagnetic pole (VGP) position of Plat ¼ 718N, Plon ¼ 1138E (A 95 ¼ 8.18). Although secular variation may not have been fully averaged out, the new VGP provides an important result to define the late Mesoproterozoic position of Baltica. The VGP is not close to any known Proterozoic palaeopoles of Baltica, and therefore the pre-Sveconorwegian apparent polar wander path (APWP) of Baltica must be modified. The pre-Sveconorwegian (c. 1.3-1.0 Ga) APW swathes of Baltica, Laurentia (including the Logan Loop) and Kalahari cratons show similar shape, but new well-dated palaeomagnetic poles for c. 1.25-1.12 Ga interval from these continents are required to test the similarity. The Salla dyke VGP provides hints that the Mesoproterozoic Baltica-Laurentia connection in the Hudsonland supercontinent assembly lasted until 1.12 Ga.

The palaeomagnetically viable, long-lived and all-inclusive Rodinia supercontinent reconstruction

“…Relative to Laurentia, Baltica rotated clockwise c. 708 about an Euler pole near Scoresby Sund, some time between 1270 and 1050 Ma, in approximately the same sense as was first proposed by Patchett et al (1978) and Piper (1980). New palaeomagnetic results from the 1122 Ma Salla Dyke in northern Finland are more compatible with a pre-rotation reconstruction than a post-rotation reconstruction, suggesting that the rotation occurred after, or even coincident with, dyke emplacement at c. 1120 Ma (Salminen et al 2009). The proposed rotation is consistent with the broad-scale tectonic asymmetry of Baltica (orogeny in west, rifting in east) through the Mesoproterozoic interval .…”

Generation and preservation of continental crust in the Grenville Orogeny

“…Several workers propose that the Torridon Group was deposited in a series of extensional basins that formed during the late-stages of the Grenville Orogeny (Soper and England, 1995;Williams and Foden, 2011). The clockwise rotation of Baltica (between w1120 and 1000 Ma; Salminen et al, 2009;Cawood et al, 2010) and the accompanying opening of the Asgard Sea (between Greenland and Baltica, Fig. 2) facilitated post-Grenville convergence during the Renlandian Orogeny.…”

Laurentia-Baltica-Amazonia relations during Rodinia assembly

“…The third pole from ca. 1120 Ma Salla dyke (Salminen et al, 2009) is supported by a contact test, but unfortunately the remanence direction of the unbaked host rock is close to the dyke direction, which somewhat undermines the reliability of this test. In addition, this pole is based on just one dyke, so the geomagnetic secular variations are not averaged.…”