N. Badertscher et M. Burkhard, Alpine inversion of the Permo-Carboniferous Salvan-Dorenaz Graben and its relation with the overlying Morcles nappe, ECLOG GEOL, 91(3), 1998, pp. 359-373
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.