Consequences of thrusting and intraplate stress fluctuations for vertical motions in foreland basins and peripheral areas

SUMMARY We present a conceptual model for short‐term and long‐term alternations in subsidence and uplift in foreland basins. Convergence of lithospheric plates produces forces at the plate boundaries, generating stresses in the accretionary wedge, the underthrusted crust, and the lithosphere. When the stresses reach the shear strength of the rocks in these units, deformation, which results in the redistribution of mass, takes place contemporaneously with reduction of the stress level. Modelling of both the effects of this alternating building up and relaxation of stress, and the effects of the resulting mass redistribution on foreland basin geometry, employing an elastic rheology of the lithosphere, demonstrates that these processes exert an important control on the shape of foreland basins. Vertical motions take place on different time‐scales dependent on the scale of thrusting and the style of deformation. Short‐term (10–10 4 yr) vertical motions are related to small‐scale thrust events, while long‐term vertical motions are induced by larger scale deformation in the overriding thrust wedge. Furthermore, the geometry of faults influences the duration of the magnitude of stress fluctuations. Stress‐induced alternations of subsidence may lead to the deposition of alternating sequences in foreland basins on scales of centimetres (e.g. cyclothems) to scales of several hundreds of metres (on‐lap and off‐lap sequences). In this respect, the mechanical coupling between convergent zones and peripheral areas is of particular importance, as it induces simultaneous alternations in regional facies patterns. The model also provides an explanation for vertical motions in the foreland basin previously attributed to visco‐elastic relaxation processes.