Flexural expression of European continental lithosphere under the western outer Carpathians

We present the results of an analysis of the flexural down bending of the European lithosphere under the western outer Carpathians for a grid of five profiles with a lateral spacing of about 100 km crossing the Carpathians and its foreland. Seismic sections, including two deep seismic reflection lines, and numerous wells allowed us to quantify the flexural curvature of the lithosphere. In addition, gravity data are used to obtain independent constraints. Two evolutionary scenarios involving subduction/underthrusting of passive margin and a phase change in the lower crust are investigated in a context of relatively flat Moho under the area. Furthermore, recent uplift, expressing itself in erosional features observed along the distal margin of the foredeep, is quantified. The generally modest Bouguer gravity anomaly points to nonisostatic processes causing this uplift. Steeply dipping basement under the Carpathians to about 10 km depth at the location of the Pieniny Klippen Belt is explained by relatively weak lithosphere, which is expressed in the predicted low values of effective elastic thickness of 16 km decreasing locally to 3 km. The low strength of the European lithosphere in this region is probably caused by mechanical weakening controlled by partial yielding due to high flexural curvature. The weakest parts of the lithosphere along the profiles, corresponding to low effective elastic thickness, are concentrated in the areas of maximum bending. Predicted flexural bending stresses as a function of bending moment and effective elastic thickness increase dramatically under the outer zone of the Carpathian belt, explaining reactivations of older basement structures in these regions.