Caledonian and Proterozoic terrane accretion in the southwest Baltic Sea

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