On the palaeogeography of Baltica during the Palaeozoic: new palaeomagnetic data from the Scandinavian Caledonides

Abstract

SUMMARY Based on new palaeomagnetic results from the North Norwegian Caledonides, we propose new apparent polar wander paths for Baltica during the Early-Mid Palaeozoic and discuss their palaeogeographic implications. In Cambrian and Early Ordovician times, Baltica occupied southerly latitudes of the order of 30 to SO, but was 'inverted' with respect to its present orientation. Consequently, the Russian Platform faced Avalonia and Gondwana, the latter continent occupying high southerly latitudes. Closure of the Tornquist Sea was then accompanied by continental scale, anticlockwise rotation of Baltica relative to Avalonia. This rotation probably occurred during mid-Ordovician times, although as yet, the timing of final suturing is poorly constrained by available palaeomagnetic data. At this time Laurentia occupied an equatorial position. Baltica then moved northwards in Late Ordovician and Silurian times, and subsequently collided obliquely with Laurentia to produce the Mid-Silurian to Early Devonian Scandian Orogeny . Oblique convergence set up sinistral orogen-parallel shear zones, on which major movements ceased by Late Silurian times. After amalgamation, Baltica and Laurentia occupied equatorial to tropical southerly latitudes. Reconstructions for the Siluro-Devonian boundary are now relatively straightforward. Euramerica was assembled by that time, and occupied equatorial (N. Baltica) to high (c. 60) southerly latitudes (S. Laurentia) prior to northerly movement and the final assembly of Pangea.