Reconstructing the Evolution of Foreland Fold-And-Thrust Belts Using U-Pb Calcite Dating: An Integrated Case-Study From the Easternmost Jura Mountains (Switzerland)

Abstract

This case-study from the Jura Mountains in the foreland of the European Alps demonstrates how the coupling of subsurface analysis and U-Pb carbonate dating can provide absolute timing constraints and shortening rate estimates of fold-and-thrust belts. It is confirmed that the initial Late Cenozoic foreland deformation driving the formation of the easternmost Jura Mountains in Switzerland was predominately thin-skinned with contractional deformation largely restricted to the Mesozoic succession above a sub-horizontal basal décollement. Thereby, the localization and structural style of related deformation structures was strongly guided by the characteristics of underlying Late Paleozoic half grabens. The main thin-skinned thrust front formed at ∼12 Ma, followed by further deformation in the hinterland and locally continued foreland-directed thrust propagation. The major deformation zones exposed at surface were established at ∼8 Ma but shortening continued until at least ∼4 Ma. Thick-skinned contraction associated with the inversion of basement structures only played a subordinate role during the latest deformation phase after 8 Ma. Based on cumulative shortening values derived from balanced cross sections, our U-Pb ages of syn-tectonic calcite slickenfibres allow to estimate thin-skinned deformation rates for the easternmost Jura Mountains between ∼0.9 and ∼0.1 mm/year, decreasing toward the eastern tip of the arcuate belt. Moreover, deformation rates seemingly decreased over time with rates of initial thin-skinned thrusting being significantly higher than the later deformation north of the main thrust front. These new findings from a classical foreland setting highlight the potential of integrating U-Pb dating in regional fold-and-thrust belt investigations elsewhere.