Palaeoproterozoic Laurentia-Baltica relationships: a view from the Lewisian

Using a modified Patchett et al. (1978) pre-Grenville fit of Laurentia and Baltica, tectonic information from the Lewisian complex of Britain and from neighbouring Palaeoproterozoic belts of Laurentia and Baltica is reviewed. It is shown that a remarkable consistency in convergence directions existed across the whole region in the period 1.9–1.8 Ga suggesting that the reconstruction used may be correct, and that a common movement pattern can be inferred for the Palaeoproterozoic period within the North Atlantic region. A speculative plate tectonic history for the region between c. 2.6 and c. 1.5 Ga is discussed in four stages. (1) 2.6–2.4 Ga: development of conjugate shear-zone systems in the North Atlantic craton. (2) 2.4–2.0 Ga: rifting and dyke emplacement in older cratons; creation of oceanic and intracontinental basins. (3) 2.0–1.8 Ga: subduction at active margins of older cratons with creation of magmatic arcs; collision of cratons accompanied by closure of intra-cratonic basins and accretion of arc terranes. (4) 1.8–1.5 Ga: development of new active margin discordant to the previous ones, with significant changes in convergence direction within the amalgamated continental assembly.