Collision tectonics in the Western Alps

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Abstract
Summary: This paper gives a brief review of some different models that have been proposed to account for the tectonic development of the Western Alps, emphasizing the field evidence which indicates the major role played by strike-slip tectonics. Sketch maps of the tectonic evolution since Cretaceous times are presented which interpret the Alps as a strike-slip collision belt followed by ‘hypercollision’ on the western edge of the northward-moving Adriatic Promontary. There was early local collision along N-S strike-slip faults, while intervening E-W trending basins remained open. General collision is considered to have been completed by Eocene times when the pre-existing basins disappeared and the previously stretched lithosphere was restored to normal thickness. The following hypercollision first continued along the same N-S strike-slip displacements, with thickening of the lithosphere and migration of flysch basins. Later Oligocene hypercollision evolved into mainly westward displacement, limited by E-W strike-slip zones, dextral in the N and sinistral in the S. Strike-slip collision and hypercollision are considered as sufficient to explain the particuliarities of the tectonic development of the Western Alps, with associated metamorphisms and basinal evolution, since 80 Ma.