Between the original position and their present day location as klippen,
the Prealpes Medianes underwent a complex history of paleotectonics and
alpine tectonics. Due to the opening of the Piemont ocean the
Brianconnais sedimentation realm of the Prealpes Medianes evolved as a
rim basin of the northern passive margin during Jurassic to Eocene
times. Different paleotectonic features (normal faults, synsedimentary
growth structures, inversion structures) developed and were active above
a basal detachment in evaporitic layers. The tectonic movements were a
consequence of thermal events in the crust. Isolated from the Iberic
continent at the end of the Late Cretaceous, the Brianconnais exotic
terrain was incorporated into the accretionary prism of the closing
Piemont ocean and the incipient alpine orogeny during the
Lutetian-Bartonian. The Prealpes Medianes were detached from their
homeland during the Bartonian-Priabonian and were transported onto the
foreland. The tectonic style is one of a thin-skinned foreland fold and
thrust belt. Fault associated fold development above a main decollement,
together with internal deformation, represent the Prealpes Medianes main
structural features. The very low-grade metamorphic conditions have
their origin in the heat flux induced by tectonic burial by overriding
nappes in the accretionary prism. After having been transported on top
of the developing Helvetic nappes the Prealpes were emplaced in their
present day position in front of the Alpine mountain belt during
Oligocene times. Post-emplacement and out of sequence thrusting,
possibly younger than Oligocene, is observed and can be related to
thrusting in the sedimentary substratum and the basement.