An unusual triangle zone in the external northern Alpine foreland (Switzerland): Structural inheritance, kinematics and implications for the development of the adjacent Jura fold-and-thrust belt

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.

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Structural inheritance and cenozoic stress fields in the Jura fold-and-thrust belt (France)

Tectonophysics ◽

10.1016/s0040-1951(02)00366-9 ◽

2002 ◽

Vol 357 (1-4) ◽

pp. 137-158 ◽

Cited By ~ 42

Author(s):

C Homberg ◽

F Bergerat ◽

Y Philippe ◽

O Lacombe ◽

J Angelier

Keyword(s):

Stress Fields ◽

Thrust Belt ◽

Structural Inheritance ◽

Fold And Thrust Belt

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

Solid Earth ◽

10.5194/se-11-1823-2020 ◽

2020 ◽

Vol 11 (5) ◽

pp. 1823-1847

Author(s):

Samuel Mock ◽

Christoph von Hagke ◽

Fritz Schlunegger ◽

István Dunkl ◽

Marco Herwegh

Keyword(s):

Late Miocene ◽

Late Stage ◽

Thrust Belt ◽

Central Alps ◽

Slab Geometry ◽

Long Wavelength ◽

The North ◽

Fold And Thrust Belt ◽

Alpine Foreland ◽

Main Deformation

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.

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Building a valid structural model in a triangle zone: An example from the Neuquén fold and thrust belt, Argentina

Interpretation ◽

10.1190/int-2015-0014.1 ◽

2015 ◽

Vol 3 (4) ◽

pp. SAA117-SAA131 ◽

Cited By ~ 4

Author(s):

Gonzalo Zamora-Valcarce ◽

Tomás Zapata

Keyword(s):

Structural Model ◽

Seismic Interpretation ◽

Fold Axis ◽

Thrust Belt ◽

Systematic Analysis ◽

Triangle Zone ◽

Fold And Thrust Belt ◽

Basement Fault ◽

New Interpretation ◽

Surface Geology

Structural modeling and systematic analysis are necessary in complex areas even before seismic interpretation. Seismic data in these zones usually show poor-quality images of the geologic elements. Therefore, a detailed analysis of the available information (e.g., seismic, previous wells, and surface geology) is needed to build a comprehensive structural model to constrain the seismic interpretation. Although a restorable structural cross section is not necessarily the unique solution, it is a valid interpretation to begin with, which can be tested against additional information. As an example, a structural profile interpretation in the Agrio fold and thrust belt of the Neuquén Basin, northeastern Argentina, is presented and described as invalid on the basis of several unrestorable geometric components. This led to the reevaluation of the structure to understand its possible exploratory potential. Integration of different data such as regional structural styles inferred fault trajectories from seismic reflection termination patterns, synorogenic deposit geometries in seismic, and surface geology, dipmeter data to identify the presence and location of fault position and vergence of the fold axis, and a kinematic forward model, resulted in a new restorable structural model. The new interpretation proposes a “broken triangle zone” framed by two opposite surface anticlines with the same detachment level, later faulted by a basement fault. The interpreted model suggests at least two phases of deformation (1) a thin-skinned phase with the two opposite anticlines sharing the same detachment level that is responsible for about 80% of the shortening and (2) a thick-skinned phase from an east-verging basement fault, transporting the western anticline and crosscutting the eastern anticline, that is responsible for 20% of the shortening and the synorogenic deposits at the frontal region. This new interpretation defined a new exploration prospect drilled by a wildcat well, which validated the interpretation and model predictions.

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