Palaeomagnetism and continental collision in the Alpine Belt and the formation of late-tectonic extensional basins

New palaeomagnetic data are consistent with the hypothesis that Adria moved as a promontory of the African Plate during the Mesozoic. This hypothesis is supported by regional facies analysis and by geophysical data from the eastern Mediterranean basins which indicate a continental lithosphere. However, the new data cast doubt upon the concept of a rigid, autochthonous African promontory remaining coherent during Alpine deformation. It is apparent that small-scale relative rotations have occurred during the Tertiary in areas which were previously considered authochtonous. Late-tectonic extensional basins, such as the Tyrrhenian Sea, are superimposed on the continent-continent collision suture and their growth is contemporaneous with thrusting in surrounding arcs. The very rapid evolution of the collision suture into a region of extension is due to a rapid lithospheric thinning process, such as catastrophic delamination of part of the mantle lithosphere. Such delamination would be most likely to occur very soon after a collision involving fast lithospheric thickening.