The effect of plate stresses and shallow mantle temperatures on tectonics of northwestern Europe

Northwestern Europe is tectonically more active, in terms of seismicity, ve rtical motions and volcanism, than would be expected from its location far from any plate boundaries. In the context of the Netherlands Earth System D ynamics Initiative, we investigated the implications of two recent modeling efforts, of Eurasian plate forces and European mantle structure, for our u nderstanding of the dynamics of these intraplate tectonics. We find that: ( 1) a simple balance between ridge push and collision forces along the south ern European boundary does not seem sufficient to explain the observed dire ction of maximum horizontal compression in northwestern Europe. Our stress model, which imposes dynamical equilibrium on the full Eurasian plate, pred icts that collision forces along the African-European boundary are relative ly weak and have only a minor effect on the stress field in northwestern Eu rope; (2) seismic velocity anomalies in the shallow mantle imply 100-300 de greesC variations in temperature under northwestern Europe. This regional m antle structure probably plays a significant role in the high level of intr aplate tectonic activity and the regional variations in stress and tectonic style. For most tectonically active areas in Europe, observed surface heat flow anomalies coincide with anomalies in mantle velocity. Low velocity an omalies under northwestern Europe coincide with areas of recent volcanism a nd uplift, but are offset from the regions of maximum surface heat flow. Th is suggests that the thermal regime of the central European lithosphere is not in a steady state, probably due to changing mantle conditions. The effe ct of strong variations in lithospheric strength, predicted from the modele d thermal gradients in the shallow mantle, and of dynamic stresses induced by proposed active mantle upwellings may account for (some of) the differen ces between the observed and modeled stress field and will be investigated in future stress models. (C) 2000 Elsevier Science B.V. All rights reserved .