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Absolute age and temperature constraints on faulting along the basal décollement of the Jura fold-and-thrust belt from carbonate U-Pb dating and clumped isotopes
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  • Nathan Looser,
  • Herfried Madritsch,
  • Marcel Guillong,
  • Oscar Laurent,
  • Stephan Wohlwend,
  • Stefano M. Bernasconi
Nathan Looser
Department of Earth Sciences, ETH Zurich

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Herfried Madritsch
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Marcel Guillong
Department of Earth Sciences, ETH Zurich
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Oscar Laurent
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Stephan Wohlwend
Department of Earth Sciences, ETH Zurich
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Stefano M. Bernasconi
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During its late-stage evolution, the European Alpine orogen witnessed a northwest-directed propagation of its deformation front along an evaporitic basal décollement into the foreland. This resulted in the decoupling of the northern Alpine Molasse Basin from its basement and the formation of the Jura fold-and-thrust belt. Here, we present the first absolute age and temperature constraints on deformation along this basal décollement using combined carbonate U-Pb LA-ICP-MS dating and clumped isotope thermometry. We analyzed calcite veins associated with a thrust fault branching off from the basal décollement in the distal Molasse Basin and slickenfibers from thrusts and strike-slip faults in the eastern Jura Mountains. Our U-Pb data provide evidence for tectonic activity related to Alpine contraction in this region between ~14.5 Ma and ~4.5 Ma ago. Accordingly, the propagation of Alpine deformation into the distal foreland along the basal décollement occurred earlier than commonly inferred by biostratigraphy, at Middle Miocene (Langhian) times at the latest. Younger deformation ages between ~11.5 and ~4.5 Ma correspond very well in time with shortening in the Subalpine Molasse and the Central Alps proving simultaneous tectonic activity along both thrust fronts; e.g. the Jura Mountains and the Subalpine Molasse. Clumped isotopes reveal vein calcite precipitation at temperatures between 53 and 104 °C from fluids with oxygen isotope compositions between -6.2 and +9.5 ‰. Our data show that the burial conditions in the studied area remained constant between ~14.5 Ma and ~4.5 Ma indicating that the previously reported large-scale foreland erosion initiated after ~4.5 Ma.