Supplementary material - Pre-existing basement faults controlling deformation in the Jura Mountains fold-and-thrust belt: insights from analogue models
We conducted brittle-viscous analogue models to test the influence of pre-existing fault-steps on the evolution of structures in a viscous layer overlain by a brittle cover of fine quartz sand (Schori et al., submitted). The brittle layer is pushed horizontally (from right to left in videos and CT cross-sections). The viscous layer is ca. 13 mm thick and is made of a viscous mixture of Polydimethylsiloxane (PDMS) and corundum sand that has a density of ca. 1600 kg/m^3 (Zwaan et al., 2018). The brittle layer has a thickness of 70 mm (except in model U20-45°-RC, where the thickness is 40 mm) and consists of quartz sand that has a bulk density of 1560 kg/m^3 (Klinkmüller et al., 2016). Analogue models test oblique and frontal fault-steps and represent the case of the Jura Mountains fold-and-thrust belt (JFTB) in the Northern Alpine Foreland, where pre-existing faults in the pre-Mesozoic basement are suspected to have localised and controlled deformation during JFTB evolution (Laubscher 1961). The viscous layer at the base simulates a décollement zone consisting of Trassic evaporites (salt and anhydrite), whereas the brittle quartz sand layer simulates the Mesozoic carbonate cover (limestone, dolomite, marl) of the JFTB. Further detailed descriptions of the model set-up, model results and interpretation are provided in Schori et al. (submitted). This supplementary material contains top-view videos of 18 brittle-viscous analogue models, which feature flat-base, frontal and oblique steps. Thick, black lines across the models indicate the position of the vertical base-plate step (absent in flat-base models F1 and F2). Thin black lines to the left and right of the step indicate the calculated position of thrusts at the surface, which nucleate above the step (step-controlled thrusts). The dip angle of thrust planes, used to calculate the position of step-controlled thrust lines, is given in the parameter list at the bottom left of each video. The parameters specify (1) the throw of the base-plate step and the obliquity angle α of the oblique step in respect to frontal steps (α = 0°). (2) Scaling ratio of the image in pixels per centimetres. (3) The dip of the thrust plane used to construct the line of step-controlled fore-thrusts (thin, black line to the left of the step). (4) The dip assumed to construct the step-controlled backthrust line (thin, black line to the right of the step). (5) Velocity of backstop displacement. (6) Thickness of the brittle cover. (7) Thickness of the viscous base layer with comments in case of uneven distributions. In addition to top-view videos, this supplementary material also comprises a PDF file with five cross-sections across model U20-45°-CT, which features an oblique upward step with a throw of 20 mm and an obliquity angle α = 45°. Cross-sections are raw slices across computed tomography (CT) scans of model U20-45°-CT. CT-scans were conducted in 15 minute intervals.