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

Luca Smeraglia,Nathan Looser,Stefano M Bernasconi,Flavien Choulet,Olivier Fabbri,Marcel Guillong

doi:10.5194/se-12-2539-2021

Luca Smeraglia, Nathan Looser + Show 4 more

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https://doi.org/10.5194/se-12-2539-2021

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Abstract

Abstract. 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 fold-and-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 ∼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.

Highlights

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
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
Foreland fold-and-thrust belts develop at the external edges of orogens and are characterized by a multiphase tectonosedimentary history including pre-orogenic sedimentation, uplift at the peripheral bulge of the advancing orogen, progressively accelerating subsidence followed by syn-orogenic sedimentation, and accretion of the sedimentary cover into the fold-and-thrust belt (Lacombe et al, 2007)

Summary

Introduction

Foreland fold-and-thrust belts develop at the external edges of orogens and are characterized by a multiphase tectonosedimentary history including pre-orogenic sedimentation, uplift at the peripheral bulge of the advancing orogen, progressively accelerating subsidence followed by syn-orogenic sedimentation, and accretion of the sedimentary cover into the fold-and-thrust belt (Lacombe et al, 2007). Deciphering the different tectonic phases is complicated due to the overprinting of inherited structures by progressively younger tectonic events This issue is addressed by dating syn-tectonic sediments and, more recently, better constrained through the dating of fault activity with K–Ar, 40Ar/39Ar, and U–Pb and U–Th methods (Van der Pluijm et al, 2001; Vrolijk et al, 2018). Calcite U–Pb and U–Th geochronology (Roberts et al, 2020) is the unique method for dating syn-tectonic calcite mineralizations. This technique has been applied for dating single faults in extensional, strike-slip, and compressional settings (Goodfellow et al, 2017; Nuriel et al, 2017; Hansman et al, 2018; Smeraglia et al, 2019; Carminati et al, 2020). The dating of multiple faults at the regional scale across a foreland fold-and-thrust belt remains rare (Beaudoin et al, 2018; Looser et al, 2021)

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