The Ambin massif, south of the Mont Cenis col, Savoie (France), on the Italian border, appears as a window below the Schistes lustres nappe. It consists of a Permo-Carboniferous core, overlain by autochthonous Mesozoic rocks (Brianconnais facies), which were partially eroded before emplacement of the overriding nappe. The Mesozoic cover was metamorphosed at the same time as the Permo-Carboniferous core, and their present distinct aspects are due to their originally different chemical compositions. Emplacement of the nappe was accompanied by local slicing and folding. Later the nappe and its substratum were deformed together.