Strain-displacement compatibility and restoration of the Chaînes Subalpines of the western Alps

Summary Finite strain values and trajectories of the sedimentary cover of the French Chaînes Subalpines (Chartreuse, Vercors, Diois, Baronnies) with respect to the stable platform west of these regions were deduced from the strain measurements of a folded and faulted competent layer (Tithonian). The removal of this finite deformation was obtained by a finite element analysis (84 elements of initial size of about 15×15 km) and the finite displacement field of this cover was calculated. Assuming a stable margin (one fixed element, and one line with a constant direction during the progressive deformation) the displacement of the eastern, southern and western limits of the Chaînes Subalpines were estimated. A displacement towards the west, associated with a counterclockwise rotation (15–20°) was found for the Miocene—Present basement thrust of the Belledonne massif. The presence of local heterogeneities (such as Jurassic normal faults) deflect the general E-W displacement along dextral NE-SW and N-S strike-slip faults and induce a displacement of the Chaînes Subalpines towards the southwest. The comparison of the restored depth of the Tithonian with its estimated initial depth reveals an excess of elevation of the Chaînes Subalpines with a maximum value (1000–1500 m) for the Diois—Vercors which might be associated with an external basement thrust under the Chaînes Subalpines.