U-Pb dating of middle Eocene-Pliocene multiple tectonic pulses in the Alpine foreland

Foreland fold-and-thrust belts (FTBs) record long-lived tectono-sedimentary activity, from passive margin sedimentation, flexuring, and further evolution into wedge accretion ahead of an advancing orogen. Therefore, dating fault activity is fundamental for plate movement reconstruction, resource exploration, and earthquake hazard assessment. Here, we report U-Pb ages of syn-tectonic calcite mineralizations from four thrusts and three tear faults sampled at the regional scale across the Jura fold-and-thrust belt in the northwestern Alpine foreland (eastern France). Three regional tectonic phases are recognized in the middle Eocene-Pliocene interval: (1) pre-orogenic faulting at 48.4 +/- 1.5 and 44.7 +/- 2.6 Ma associated with the far-field effect of the Alpine or Pyrenean compression, (2) syn-orogenic thrusting at 11.4 +/- 1.1, 10.6 +/- 0.5, 9.7 +/- 1.4, 9.6 +/- 0.3, and 7.5 +/- 1.1 Ma associated with the formation of the Jura foldand-thrust belt with possible in-sequence thrust propagation, and (3) syn-orogenic tear faulting at 10.5 +/- 0.4, 9.1 +/- 6.5, 5.7 +/- 4.7, and at 4.8 +/- 1.7 Ma including the reactivation of a pre-orogenic fault at 3.9 +/- 2.9 Ma. Previously unknown faulting events at 48.4 +/- 1.5 and 44.7 +/- 2.6 Ma predate the reported late Eocene age for tectonic activity onset in the Alpine foreland by similar to 10 Myr. In addition, we date the previously inferred reactivation of pre-orogenic strike-slip faults as tear faults during Jura imbrication. The U-Pb ages document a minimal time frame for the evolution of the Jura FTB wedge by possible in-sequence thrust imbrication above the low-friction basal decollement consisting of evaporites.

Automated summary

The study reports U-Pb ages of syn-tectonic calcite mineralizations from different periods in the Jura fold-and-thrust belt in eastern France and identifies three regional tectonic phases. During this time, pre-orogenic faulting, syn-orogenic thrusting, and syn-orogenic tear faulting occurred, revealing a complex history of tectonic activity in the region.