Dynamics of intra-plate compressional deformation: the Alpine foreland and other examples

Abstract

Intra-plate compressional structures, such as inverted extensional basins and upthrusted basement blocks, play an important role in the tectonic framework of the European Alpine foreland. Similar structures are observed on many continental cratons but occur also in oceanic basins and more rarely along passive continental margins. The World Stress Map shows that horizontal compressional stresses can be transmitted over great distances through continental and oceanic lithosphere. Although a number of geodynamic processes contribute to the build-up of intra-plate horizontal compressional stresses, forces related to collisional plate interaction appear to be responsible for the most important intra-plate compressional deformations. Such deformations can involve whole-lithosphere buckling and folding, crustal folding and, by reactivation of pre-existing crustal discontinuities, upthrusting of basement blocks and inversion of tensional hanging-wall basins. Mechanical aspects of basin inversion depend on the interplay of stresses and rheology of the lithosphere. Pre-existing crustal discontinuities weaken the lithosphere and play a crucial role in localizing intra-plate compressional deformations. Reactivation of relatively steeply dipping normal faults occurs when the angle between their strike and the compressional stress trajectory is smaller than 45°. Compressional deformations restricted to crustal levels involve ‘simple-shear’-type detachment of the crust at the level of the rheologically weak lower crust from the mantle-lithosphere; whole-lithospheric ‘pure-shear’-type compressional deformation is indicated for certain inverted basins. A distinction must be made between collision-related and anorogenic compressional/transpressional intra-plate deformations. The hypothesis is advanced that the stratigraphic record of collision-related intra-plate compressional deformations can contribute to the dating of orogenic events affecting the margin of the respective craton.