Plastic velocity vector diagrams applied to indentation and transpression in the Alps

Alpine collision tectonics has affected the European Alps for more than 110 Ma and is probably still active today. The cumulative large-scale convergence in the Alps adds up to 1100 km. About 500 km of this convergence can be budgeted by escape tectonics, 300 km by continental and oceanic subduction, and an equal amount by crustal thickening. Considerable uncertainty still exists as to the kinematics of the collision; a transpressive indentation of a more or less rigid “Italy/Adria” block into a deformable European plate appears likely. In recent surveys of horizontal mass transfer in the Alps, as inferred from structural analyses, a dominant westwards directed flow regime has been recognized. Theoretical indentation models have been applied to explain the palaeo-flow field. The flow can be explained by: Case I normal indentation without transpression but a space restriction to the east. A palinspastic space restriction did not exist, on the contrary, remnant oceanic terrain survived longest in the east; Case II dextral transpression with no significant indentation. This would require an age progression of westward flow from the east (oldest) to the west (youngest) which is not observed; and Case III transpressive indentation with a sinistral shear component. This seems to be the most satisfactory solution as it explains large-scale sinistral lineaments, and leaves palinspastic space for the rapid rotation of Corsica and Sardinia.