Double evaporitic décollements: Influence of pinch-out overlapping in experimental thrust wedges

• Analogue modelling of thrust systems with two décollements.
• Structures formed include two-level thrust sequences with different geometry.
• Overlap between basal and upper décollements promotes forelandwards deformation.
• Geometry and activity of structures is controlled by the basal/upper décollement offset/overlap.
• Interaction between Triassic and Eocene décollements in the Pyrenees is consistent with analogue models.

This article focuses on how deformation and displacements are transferred between two décollements located at different stratigraphic levels by means of analogue modeling using brittle/viscous, sand/silicone systems. We present results from ten analogue models, in which we varied key parameters, such as the amount of horizontal offset or overlap between the pinch-outs of the upper and lower décollements, the total amount of shortening, and the planform geometry of the upper décollement. Results indicate that (i) structures root onto the basal and upper décollement, defining an inner and an outer domain and (ii) the offset/overlap of the décollements controls the geometry of the transition zone located between the two décollements, the propagation of deformation into the foreland both in space and time, and the deformation style and kinematics in the different domains of the model. When the pinch-out of the upper décollement is at an angle with the backstop, oblique structures form, and the geometry and propagation-mode of the structures change progressively along-strike. We compare our experimental results with other silicone/sand analogue models and with the natural examples of the Southern Pyrenees, where Upper Triassic and Eocene–Oligocene syn-tectonic evaporites acted as basal and upper décollements, respectively.