CLOSURE OF THE TORNQUIST SEA - CONSTRAINTS FROM MONA-LISA DEEP SEISMIC-REFLECTION DATA

Deep seismic reflection profiles west of Denmark across the suture bet ween Baltica and Eastern Avalonia reveal weak, southward-dipping refle ctors within the crystalline basement. These reflectors are interprete d as thrusts resulting from emplacement of Eastern Avalonia onto the s outhern edge of Baltica. North of these reflectors are the remains of a dissected Silurian foredeep. The presence of this foredeep and the 4 40 Ma age of metamorphism in rocks recovered from boreholes into Easte rn Avalonian rocks suggest that closure of the Tornquist sea occurred in the Late Ordovician, which is consistent with paleobiogeographic da ta and paleomagnetic apparent polar wander paths for Eastern Avalonia and Baltica. The similarity between these reflection data and the BABE L AC profile permits correlation of reflectors beneath Denmark into th e southern North Sea.