Caledonian and Proterozoic terrane accretion in the southwest Baltic Sea

A marine seismic reflection survey was carried out in 1996 by DEKORP, Potsdam, and BGR, Hannover in the SW Baltic Sea. Several tectonic lineaments were crossed nearly perpendicularly, for example, the Caledonian Deformation Front which is assumed to mark the northern boundary of the terrane Avalonia which accreted to Baltica ca. 400 Ma. Here, a bivergent collision is clearly observed, confirming early ideas from the BABEL survey. The NE-dipping reflections in the uppermost mantle are interpreted as signs of the subducted Tornquist Ocean. A similar tectonic style of compression and indentation is observed in the Proterozoic crust northeast of Bornholm, where in addition a remarkable crustal thickening and a strong increase of reflection power is observed. The three DEKORP lines in this area provide a certain three-dimensional control and allows extension of similar observations from the BABEL line A southward. This Proterozoic terrane accretion seems to be connected to major tectonic lineaments in southern Sweden, either to the Gothian Thrust or the Sveconorwegian Front. (C) 1999 Elsevier Science B.V. All rights reserved.