Role of sedimentation during basin inversion in analogue modelling

Sand-box experiments were designed to reproduce the effect of sedimentation during extensional basin development and tectonic inversion. These experiments were motivated by growing evidence for tectonic inversion in early Miocene times of an extensional basin (Abanico Basin) in the central Chilean Andes with contemporaneous intense volcanic activity. The experiments perform an extension followed by compression. The first series of experiments were performed without sedimentation in the developing basin; the second series were performed with partial filling of the basin, and the third series with total filling of the extensional basin. The effect of sedimentation on the sides of the basin was also controlled. Compression experiments reproducing tectonic inversion of the previously developed extensional basin were also performed with and without coeval sedimentation (series with null, partial or total fill, and also external sedimentation). The analogue experiments show that high amounts of sediments accumulated during the evolution of an extensional basin enhance subsidence and lead to the development of shortcuts in the footwall of the basin bounding faults during tectonic inversion. During extension the earliest appearance of normal faults occurs in the compartment with the greater sedimentary fill, and this causes asymmetric basin development. The post-extension compressional models show that the greater burden caused by a thicker accumulation of sediments within the basin inhibits tectonic inversion, causing the development of thrust structures rooted in the basin bounding faults. The accumulated sedimentary load affects both the extension and compression phases of the experiments, but has greater influence in the case of sedimentation during extension. A higher burden on the outer edges of the basin compared to the interior enhances the reactivation of normal faults and hampers the development of new thrust structures. The thrust fault(s) originating from the most loaded basin compartment develops as a footwall shortcut from the reactivated fault. With increasing sedimentation the shortcut is developed more superficially. The shortcut absorbs less deformation than the associated main fault.