Impact of synkinematic sedimentation on the geometry and dynamics of compressive growth structures: Analogue modelling insights

National audienceAnalogue sandbox models have been set up to study the impact of synkinematic deposits on the geometry and evolution of single thrusts and folds according to different sedimentation modes (a slow or rapid sedimentation rate that is constant or changing in space and time) and rheological profiles (thin or thick sedimentary series, with a basal décollement level or not). A first series of experiments documents the influence of synkinematic deposits according to their sedimentation rate and the rheology of the prekinematic materials. A second series investigates the influence of changes in the sedimentation rate through time. A third one considers the influence of changes in the sedimentation rate in space. All these experiments suggest that the geometry and evolution of single compressive growth structures vary according to the sedimentation rate. The number and dip of their frontal thrust segments change with the ratio R between the sedimentation rate (Vsed) at the footwall of the faults and the uplift rate (Vupl) of their hanging wall. The latter is then more or less uplifted depending on the dip of the thrusts. As a result, the overall structure has either a fault-bend fold or a fault-propagation fold geometry. Those rules are verified when the ratio R (Vsed/Vupl) changes in space or through time. In addition, the rheological profile of the models also affects the geometry and evolution of compressive growth structures. Their structural style, as well as the synsedimentary splitting and steepening of the associated thrusts, varies according to the occurrence and strength of the brittle and ductile layers. According to this modelling study, the ratio R (Vsed/Vupl) and its changes in space and time, along with the rheology of the deformed materials, are key parameters to better understand the geometrical and kinematical complexities of natural growth thrusts and folds and to improve their interpretation