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

Abstract

Abstract. In this paper, we present new exhumation ages for the imbricated proximal molasse, i.e. Subalpine Molasse, 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 massifs (i.e. external crystalline massifs) in the hinterland. Our results agree with other findings along the north Alpine foreland. While site-specific variations in the mechanical stratigraphy of the molasse deposits influence the pattern of thrusting at the local scale, we observe that late-Miocene thrusting 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 suggests 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 boundary 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 crystalline massifs, as well as the main deformation in the Jura fold-and-thrust belt are at least partly linked to changes in slab dynamics.

Chronology of thrust propagation from an updated tectono-sedimentary framework of the Miocene molasse (western Alps)

“…Between 12 Ma and 5 Ma, Molasse deposits were affected by thrusting along the ECMs borders and the entire front of the Central Alps, coeval with the main deformation phase of the adjacent Jura massif and the late exhumation of the ECMs. Hundreds of kilometers southwestwards, our results therefore support that this regional uplift probably corresponds to a tectonic event at the scale of the Alps, which may be caused by lithospheric processes (Mock et al, 2019(Mock et al, , 2020.…”

“…This adds new evidences to Deville et al (1994)'s observations postulating for a post-Langhian uplift (linked with an isostatic rebound) and the activation of out-of-sequence thrust systems in an internal position of the subalpine massifs. Interestingly, in the North Alpine foreland basin, Mock et al (2019Mock et al ( , 2020 documented a similar pattern based on low-temperature apatite (U-Th-Sm)/He thermochronometry. Between 12 Ma and 5 Ma, Molasse deposits were affected by thrusting along the ECMs borders and the entire front of the Central Alps, coeval with the main deformation phase of the adjacent Jura massif and the late exhumation of the ECMs.…”

Structural and thermal evolution of the eastern Aar Massif: insights from structural field work and Raman thermometry

“…2020 ) and break-back thrusting in the Subalpine Molasse, which lasted until at least 5 Ma (Mock and Herwegh 2017 ; Mock et al. 2020 ; von Hagke et al. 2014 ).…”

“…Deformation in the Aar Massif and other ECMs is inferred to be kinematically linked to thrusting along the Subalpine Molasse (Boyer and Elliott 1982 ; Burkhard 1990 ; Burkhard and Sommaruga 1998 ; Mock et al. 2020 ; Pfiffner et al. 1997 , 1990 , 2011 ; von Hagke et al.…”

Cenozoic Tectonic Deformation Along the Pontarlier Strike‐Slip Fault Zone (Swiss and French Jura Fold‐and‐Thrust Belt): Insights From Paleostress and Geomorphic Analyses

“…Absolute ages from different studies confirm the earlier initiation of the Jura, and the oscillating development of deformation in the detached alpine foreland. Thus, apatite fission track dating shows that thrusting in the Subalpine Molasse to the South of the Molasse Basin which occurred prior to the initiation of the JFTB, also shows pulses of thrusting between 12 and 6–5 Ma and possibly thereafter (Mock et al., 2020; von Hagke, Cederbom, et al., 2012). These ages confirm the backward stepping sequence of foreland thrusting (see also Bonnet et al., 2007, 2008).…”