Late Miocene to present deformation and erosion of the Central Alps — Evidence for steady state mountain building from thermokinematic data

We present new apatite fission track and apatite (U–Th)/He data from the Alpine orogenic front, the Austrian Subalpine Molasse. We show that the cooling signal reported from the Swiss part of the basin since 10 Ma is also present farther east. Hence, it appears to be independent of the kinematic relation to thrusting in the external thrust belt present further west, the Jura Mountains. By reconstructing the Central Alpine pro-wedge geometry at 10 Ma, we show that the taper of the Central Alps has not changed significantly and presumably remained close to the critical state since then. From cooling offsets at faults, the present day shortening rate of the pro-wedge ranges between 1.0 and 2.0 mm/a and appears to have been constant since at least the Late Miocene. In conjunction with the observations of repeated out-of-sequence thrusting in the Subalpine Molasse, a stationary deformation front, constant shortening and erosion rates and the constant taper, we argue that the Central Alpine pro-wedge is at kinematic, as well as at mass flux steady-state since 10 Ma. Our results suggest that distinct climate-driven erosion events – in contrast to more continuous erosion – are not distinguishable in the deformation record of the last 10 Ma. Hence, kinematic and mass flux steady state in the Central Alpine pro-wedge along with stable localization of deformation restricted to the Subalpine Molasse may indicate a feedback between ongoing shortening and erosion at low rates during the Late Neogene to present