Flexure of the continental lithosphere beneath Apennine and Carpathian foredeep basins

Abstract

The formation and development of foredeep basins adjacent to marginal fold and thrust belts are thought to be the result of flexural loading of the foreland lithosphere by migrating thrust sheets¹, and this concept has formed the basis for many recent studies of the deformation of the continental lithosphere and consequent evolution of foreland basins^2–7. The preservation of foredeep basins, after the associated mountain belt has been greatly reduced by erosion, suggests that an additional load, independent of the topography, must act on the lithosphere of the subducted slab⁶. To determine whether such an additional load might be present in some very young orogenic belts, we constructed transects through the Apennine and outer (flysch) Carpathian thrust belts of the Mediterranean region (Fig. 1). Using a simple elastic model, which assumes a semi-infinite (broken) elastic plate of constant flexural rigidity overlying a weak fluid, we show that the topographic loads present along these transects are insufficient to cause the observed plate deflection. This suggests that there is an additional load (or downward force) acting on the plate to produce the observed plate deflection beneath the foredeep troughs. We suggest that this extra load resulted from either the negative bouyancy contrast between the subducted slab and the surrounding asthenosphere, or modification of the crustal structure within the overriding plate due to the initiation of backarc rifting in the hinterland.