Fig. 1

a Simplified tectonic map of the north-western part of the Western Alps (modified after Le Bayon and Ballèvre 2006). E Etirol Levaz, Em Emilius, GR Glacier-Rafray, Pi Pillonet, V Verrès. Because of their small sizes, the Santanel, Tour Ponton, and Acque Rosse basement slices are not shown in the map. The outlines of the Dent Blanche Tectonic System, the Pillonet klippe, and the Sesia Zone (together referred to as the Sesia–Dent Blanche nappes) are marked by white lines; b Metamorphic map of the same area. The map combines the age and the grade (i.e. the metamorphic facies) of the Alpine metamorphism