The post-Triassic evolution of the Sorgenfrei-Tornquist Zone - results from thermo-mechanical modelling

The Sorgenfrei-Tornquist Zone (STZ) is part of the Fennoscandian Border Zon e separating the Danish Basin from the Fennoscandian Shield. The STZ as a s tructural element is of Palaeozoic origin and represents the north-westerly segment of the Tornquist-Teisseyre Zone, which separates the younger West European crust from the older East European Platform and extends from the B lack Sea to the eastern North Sea area. The STZ was reactivated in Triassic -Jurassic extension and Late Cretaceous and Paleogene compression. This paper investigates the regional geological consequences of the reactiv ations by quantitative modelling along a profile across the STZ in the Dani sh area. The numerical model invokes elastic, viscous and plastic deformati ons of the lithosphere as well as surface processes governed by erosion, se dimentation and lateral transport under the influence of eustatic sea level variations and regional isostatic compensation. Surface processes and lith ospheric mechanics are coupled through thermal blanketing effects and loadi ng. The results, in general, address the regional geological consequences of th e existence of intracontinental zones of structural weakness. More specific ally the results show that the Late Cretaceous and Paleogene chalk depocent res in the Danish Basin are a direct consequence of the inversion of the ST Z, and that the STZ inversion together with falling sea level in Cenozoic t ime are amongst the principal controlling factors in the geological evoluti on in the eastern North Sea area. (C) 2000 Elsevier Science B.V. All rights reserved.