A Multiple thermochronometer approach reveals post 12Ma tectonic activity in the foreland basin of the Northern Alps

Accelerated denudation during the late Neogene is reported from the Alpine region, but the driving mechanism behind the erosion signal is so far unknown. In order to explore this cooling signal, we use a multiple-thermochronometer approach, applying apatite fission track (FT) and (U-Th-Sm)/He dating. Combining these two thermochronometers along vertical and horizontal transects limits the possible cooling histories markedly and has major consequences for the interpretation of tectonic activity within the Alps and its foreland basin. The FT ages presented here were produced by LA-ICP-MS determination of uranium (avoiding sample irradiation). For some sample pairs of neighbouring localities and identical tectonic origin, data are compared with conventional EDM dating results. Even though differences between two sampling points might result from changes in heat flow, differential tectonic uplift or variable glacial erosion, the data produced by different analysts with an independent method reproduces well within error. The new apatite FT and (U-Th-Sm)/He data from a horizontal profile and a complementary vertical profile are presented, and pinpoint the periods of active thrusting where data offsets occur across thrusts emerging at the surface. The horizontal profile encompasses the entire Subalpine Molasse, which is the most external tectonic unit of the Alps, and a transition zone between orogen and pro-wedge foredeep. It is therefore uniquely suited to understand the potential connection between late Miocene to Pliocene erosion in the Alps and the basin itself. The cooling ages we present and the modelled cooling histories derived corroborate the idea of renewed Mid-Miocene to Pliocene thrusting in the Subalpine Molasse. Moreover, we identify different cooling events and their contribution the entire cooling signal. The discovered cooling events do not coincide with known climatic changes. Therefore, we suggest that tectonic forcing at crustal and mantle level is responsible for the observed signals.