Alpine inversion of the Permo-Carboniferous Salvan-Dorenaz Graben and its relation with the overlying Morcles nappe

The Salvan-Dorenaz <<syncline>> results from an intense late alpine folding along with moderate inversion of a Permo-Carboniferous graben fill, sittin g on top of the external crystalline Aiguilles Rouges Massif. Folds are non -cylindrical and disharmonic owing to the non-parallel, non-horizontal bedd ing plane orientation of the terrigenous sediment bodies. A concommittant w eak inversion of the graben fill by about 400 m of vertical extrusion is in dicated by the arcuate shape of the Triassic dolomites and the thrust plane of the overlying Morcles nappe. The main foliation, the SE-NW oriented str etching lineation and intense ductile folds with subhorizontal axial planes are observed within the Morcles nappe, in parautochtonous thrust slices an d in the Tertiary cover of the Aiguilles Rouges Massif. These first deforma tion structures, however, fade out rapidly towards the footwall and are vir tually absent within the Permo-Carboniferous graben fill. Upright folds wit hin the latter are due to a second alpine deformation phase. Second phase f olds within the inverted limb of the Morcles nappe have an asymmetry indica ting the <<wrong>> i.e. a normal limb, vergence, which is interpreted as du e to ongoing shear displacement towards the NW. Style differences of second phase folds between the Permo-Carboniferous graben fill, the parautochthon ous and the Morcles nappe are explained as disharmonic folding on either si de of incompetent Triassic cornieules with strongly varying thickness. Deta iled structural observations and the construction of cross sections indicat e no late Variscan compression.