DYNAMICS OF INTRAPLATE COMPRESSIONAL DEFORMATION - THE ALPINE FORELAND AND OTHER EXAMPLES

Intra-plate compressional structures, such as inverted extensional bas ins and upthrusted basement blocks, play an important role in the tect onic 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 M ap shows that horizontal compressional stresses can be transmitted ove r great distances through continental and oceanic lithosphere. Althoug h a number of geodynamic processes contribute to the build-up of intra -plate horizontal compressional stresses, forces related to collisiona l plate interaction appear to be responsible for the most important in tra-plate compressional deformations. Such deformations can involve wh ole-lithosphere buckling and folding, crustal folding and, by reactiva tion of pre-existing crustal discontinuities, upthrusting of basement blocks and inversion of tensional hanging-wall basins. Mechanical aspe cts of basin inversion depend on the interplay of stresses and rheolog y of the lithosphere. Pre-existing crustal discontinuities weaken the lithosphere and play a crucial role in localizing intra-plate compress ional deformations. Reactivation of relatively steeply dipping normal faults occurs when the angle between their strike and the compressiona l stress trajectory is smaller than 45 degrees. Compressional deformat ions restricted to crustal levels involve 'simple-shear'-type detachme nt of the crust at the level of the theologically weak lower crust fro m the mantle-lithosphere; whole-lithospheric 'pure-shear'-type compres sional deformation is indicated for certain inverted basins. A distinc tion must be made between collision-related and anorogenic compression al/transpressional intra-plate deformations. The hypothesis is advance d that the stratigraphic record of collision-related intra-plate compr essional deformations can contribute to the dating of orogenic events affecting the margin of the respective craton.