Long-wavelength late-Miocene thrusting in the north Alpine foreland: implications for late orogenic processes

In this paper, we present new exhumation ages
for the imbricated proximal molasse, i.e. Subalpine Mo-
lasse, of the northern Central Alps. Based on apatite
(U−Th−Sm)/He thermochronometry, we constrain thrust-
driven exhumation in the Subalpine Molasse between 12 and
4 Ma. This occurs synchronously to the main deformation in
the adjacent Jura fold-and-thrust belt farther north and to the
late stage of thrust-related exhumation of the basement mas-
sifs (i.e. external crystalline massifs) in the hinterland. Our
results agree with other findings along the north Alpine fore-
land. While site-specific variations in the mechanical stratig-
raphy of the molasse deposits influence the pattern of thrust-
ing at the local scale, we observe that late-Miocene thrust-
ing is a long-wavelength feature occurring along the north
Alpine foreland roughly between Lake Geneva and Salzburg.
The extent of this thrusting signal as well as the timing sug-
gests that late-Miocene thrusting in the north Alpine foreland
coincides with the geometries and dynamics of the attached
Central Alpine slab at depth. Interestingly, this implies that
the slab geometry at depth does not coincide with the bound-
ary between the Eastern and Central Alps as observed in
the surface geology. Using this observation, we propose that
thrusting in the Subalpine Molasse and consequently also the
late stage of thrust-related exhumation of the external crys-
talline massifs, as well as the main deformation in the Jura
fold-and-thrust belt are at least partly linked to changes in
slab dynamics.