FROM COLLISION TO COLLAPSE - PHASES OF LITHOSPHERIC EVOLUTION AS MONITORED BY SEISMIC RECORDS

Deep seismic reflection profiles in Europe and elsewhere cover a range of different tectonic units. Specifically, in western and central Eur ope they cross structures relating to the Alpine, Variscan and Caledon ian orogens with considerable crustal shortening, delamination, and in terfingering. The Variscan mountain belts in France and Germany show c ollapsed structures from various collision events between 300 and 350 Ma ago. Still further north in middle England and the southwest Baltic Sea traces of the Caledonian collision around 400 Ma and associated c ollapse structures are visible. Here, the terrain East Avalonia (Cadom ia) docked to the colliding continents of Baltica and Laurentia in a c omplex pattern with closing oceans and compressional boundaries, which can still be seen in today's seismic sections in Britain and the SW B altic Sea. All the processes of crustal shortening, interfingering and delamination were certainly active during the compressional stages of these earlier orogens and have left their marks, which are still reco gnizable in today's seismic image of the crust. Crustal roots and high elevations have disappeared in the extensional collapse phase, therma l events have intruded, 'underplated' or otherwise modified the stretc hed lower crust. In the Variscan internides massif granite production started, and the lower crust assumed an especially strong and thick sh eared, laminated structure with a plane Moho. The various tectonic sta ges are illuminated by a gross analysis of reflectivity patterns. We p ostulate that the fate of these patterns from their origin to their de ath is imbedded in thermally and rheologically varying creep processes , which always accompany the brittle and ductile deformation in the Ea rth's crust.