The effects of basal friction and basement configuration on deformation of fold-and-thrust belts: insights from analogue modeling

This thesis discusses the effects of basal friction and basement configuration on the deformation of the fold-and-thrust belts in convergent zones. A series of analogue models were conducted with adjacent different basal configuration and frictional properties to observe and gain a better understanding of these basal effects and their interactions. The results from these side-by-side systematic models demonstrate that the kinematics and geometry of the deformation wedges are strongly influenced by the mechanical and geometrical basal effects. In these experiments, high accuracy laser scanner and digital camera were used to record the evolution of the surface topography of the deformed sand packs. Comparison between models with different basal friction shows that the basal friction plays a significant role on the propagation and topography of the deformation structures in aspects such as wedge height, taper angle, number of imbricates and deformation front. The models with a basal viscous material, which acts as low friction substrate, illustrates that the propagation of deformation above viscous material is faster and further than above the adjacent mechanically different frictional decollement. In the experiments with a moving plate under the part of the sand pack, the velocity discontinuity was introduced by either rigid, i.e. frontal edge of the metal plate, or deformable like distal end of the viscous materials. The results of these kinds of experiments, applicable to for example basement faults, salt decollements and tectonic underplating simulations, illustrate that the deformation localizes and develops continuously above the velocity discontinuities. Besides, the different rate and distance of the propagation of deformation fronts caused by different substrate distribution between the adjacent zones also lead to the formation of transpressive zones at the boundary of these adjacent domains with different basal friction/configurations