Fold-and-thrust tectonics in the Helvetic Nappes (E Switzerland)

Summary The Helvetic Nappes in E Switzerland form an example of décollement nappes. The Säntis Thrust represents both an upper and a lower detachment. In the units underlying this detachment shortening is accomplished by a combination of folding and thrusting and is strongly influenced by the occurrence of 2nd order décollement horizons. Nappe-internal deformation resulted in the reorientation of folds (development of a fold arc) and smoothing out of ramps and flats in thrust surfaces. Two types of folds can be recognized: true buckle folds and folds due to ramps and flats. The movement direction of the thrust sheets was S-N and fold axes oblique to this direction developed probably due to initially ENE striking ramps. Transverse faults with a strike slip component allow changes in displacement along individual thrust surfaces.