Large-scale three-dimensional gravity analysis of the lithosphere below the transition zone from Western Europe to the East European Platform

Large-scale three-dimensional gravity modelling using data averaged on a 1 degrees grid has been carried out for the transition area from Western Euro pe to the East European craton. The model consists of two regional layers o f variable thickness - the sedimentary cover and the crystalline crust - wi th lateral variation of average density. Removal of the calculated gravity effect of the crustal model from the observed gravity field reveals residua l anomalies of mantle origin. This is confirmed by the correlation between mantle gravity anomalies and upper mantle velocity heterogeneities imaged b y seismotomographic studies. The Tornquist-Teisseyre Zone (TTZ), marked in general by a gradient zone of mantle gravity anomalies, is considered as a deep density section traced in the upper mantle down to a depth of 200 km. Across this suture zone a dramatic change of the structure, physical proper ties and composition of the lithosphere of the continent occurs. The differ ent characters of the mantle gravity anomalies over the two main parts of t he TTZ - the Danish-Scandinavian and Polish segments - are explained by the peculiarities of their evolution and the different character of the prevai ling tectonic regimes during the Proterozoic-Cenozoic. (C) 1999 Elsevier Sc ience B.V. All rights reserved.