Geodynamic implications of transverse folding in the Western Alps for the Alpine fold belt

LARGE amplitude translations towards the external parts of the Alpine arc are still considered as the major feature of Alpine tectonics1–5. More recent approaches, inspired by concepts of global tectonics6–8, have led to the development of new models, none of which however accounts for the widespread distribution of early transverse folds which in general are thought to have been formed either before9 or later10–13 than the overthrusting, and are considered to be minor structures. New data on the variations in strike of both transverse and longitudinal folds have been gathered over wide areas of the Alps between Savone and the Simplon Pass. The results indicate that in the whole Pennine Zone as well as part of the external zone only two important successive phases of folding have occurred, the trends of which are completely different. Here I am concerned with the ‘initial transverse phase’ or ‘main Alpine phase’ of deformation.