THE DEEP-SEISMIC IMAGE OF THE CRUSTAL STRUCTURE OF THE TORNQUIST ZONEBENEATH THE SKAGERRAK SEA, NORTHWESTERN EUROPE

In the SW Skagerrak Sea a set of deep-seismic profiles cross the Tornq uist Zone, a complex fault zone extending from the Black Sea to the No rth Sea. These sections show that the Scandinavian segment of the Torn quist Zone represents the boundary between the thick crystalline crust of the Fennoscandian Shield to the northeast and the thinner basin cr ystalline crust to the southwest. It is associated with a complex area of Moho offsets and sub-Moho reflectors. Flexural subsidence of the s hield edge appears to have occurred during the Mesozoic without substa ntial thinning of the crust. On the basin side, the thinned crust toge ther with the uppermost mantle appears to have been rigid enough to su pport segmentation and rotation of lithosphere blocks. The deep and na rrow Fjerritslev Trough is located at a bend of the Tornquist Zone and is observed to contain at least 15 km (8.5 s TWT) of sediments. It is interpreted as a pull-apart basin created by transtensional movements along the Tornquist Zone. The presence of at least 6 km (3 s TWT) of Palaeozoic sediments in the Fjenitslev Trough indicates that this segm ent of the Tornquist Zone was active also during this period. (C) 1998 Elsevier Science B.V. All rights reserved.