Effect of mechanical stratigraphy on the structure and kinematics of salt-bearing fold-and-thrust belts: Insights from scaled analogue experiments with optical strain monitoring (digital image correlation)

2D contractional scaled analogue experiments with composite materials including silica-sand and mica-flakes for overburden and silicone for salt analogue are used to investigate effects of mechanical stratigraphy on the structural evolution and kinematics of salt-detached fold-thrust-belts. Specific parameters tested are mechanical stratigraphy of the overburden and thickness variation of the basal silicone layer. The silicone-detached models in general are characterized by low-taper thrust wedge geometries and non-systematic vergence of folds and thrusts. Strain localization in the undeformed layer occurs as an in-sequence foreland breaking sequence. Strain is nucleating as detachment folds including thrust-bounded and concentric folds. Increased shortening develops break-thrusts in fold limbs. In-sequence frontal thrust interacts with out-of-sequence reactivation of older thrusts in the internal thrust wedge. Syn-kinematic silicone mobilization causes diapirism, allochthonous sheets and source-fed thrust. The specific distribution of discordant and allochthonous silicone structures vary with the mechanical stratigraphy. The impact of the mica-interlayer in the overburden sequence is strain-dependent. It strengthens the undeformed sand-pack compared to initial thrusting while active thrusts with mica-flakes in shear zones are weaker and active for longer than in homogeneous sand-pack. The longevity of thrusts correlates with the transfer of silicone to external domains and hanging-walls of thrusts. The silicone thickness controls the strain nucleation modes whether thrusting-dominated or folding-dominated predating main-thrusting stages. It also governs silicone supply and flow regimes with thick silicone source layers being readily remobilized to source-fed thrust and inflate silicone massifs in the foreland. Insights from the modelling results are that the formation of large-transport source-fed thrusts such as Quele Thrust (China) and Chazuta Thrust (Peru) observed in salt-bearing FTB's is possibly attributed to salt detachment thickness and anisotropic overburden resulting from mechanically layered stratigraphy. •Salt thickness controls deformation nucleation modes and governs viscous material supply and flow regimes.•The impact of mica interlayers is strain-dependent.•Large-transport source-fed thrust can form from salt-cored fold if there's enough salt supply and anisotropic overburden.