Fig. 4

Schematic geological profile of the Zweisimmen-Rawil-Sierre-Weisshorn-Monte Rosa transect of the Swiss-Italian Alps. The Zweisimmen-Zermatt transect is based on reflexion seismic data of the National Foundation 20 deep seismic project (Escher et al. 1997; Steck et al. 1997). In the frontal part of the Monte Rosa nappe, the axial trace of the Mondelli fold is in fact a « paleo-axial » trace that does not correspond any more today to the definition of an axial trace. This line marks the emplacement where the axial trace was after the completion of the F3 phase of folding. As curvature is a geometrical property that is not conserved by strain (even homogeneous), this trace has been transformed by younger deformation in such a way that today it is no more a locus of maximum curvature. As for the Berisal fold, the Monte Rosa border was already curved before the F5 phase, so that the point of its intersection with the Berisal axial trace is also not a point of maximum curvature of this borderline. (3) Pizzo del Vallone nappe