4D analogue models of extensional fault systems in asymmetric rifts: 3D visualizations and comparisons with natural examples

Abstract

New three-dimensional analogue modelling experiments have been carried out to simulate the development of offset and segmented asymmetric rift systems. High-resolution digital photography, combined with animations and 3D reconstructions, has enabled the detailed study of the progressive 4D evolution of these complex rift fault systems. In particular, this paper focuses upon the growth of faults at the early stages of development and the formation of accommodation zones where the rift fault architectures change along-strike. These sandbox analogue models simulate the development of asymmetric oblique rifts where the extension direction was at an average angle of 60° to the rift axis, controlled by the underlying baseplate configuration. Segmented rifts were generated by discrete offsets in the baseplates of the sandbox models. In all models the rift border faults were controlled by the orientations (and offsets) of the baseplates beneath the models whereas the intra-rift faults generally initiated at high angles to the extension direction. With increased stretching, both the rift border faults and the intra-rift faults propagated along-strike, producing segmented fault systems separated by relay ramps that were breached as fault linkage occurred. Kinks along the fault traces indicate these linkage points. In all models the asymmetric extension produced a dominant border fault system on the static rift margin, whereas the moving rift margin was characterized by domino-style extensional fault systems dipping into the centre of the rift basins. In the segmented rift models, zones of offset were characterized by complex accommodation zones formed by arrays of oppositely dipping faults. In serial cross sections the accommodation zones consisted of complex conjugate fault systems formed by the overlapping tips of oppositely dipping faults. Three-dimensional visualizations of the completed models, together with fault displacement analyses using Traptester, allowed detailed analyses and geometric reconstructions of these accommodation zones. The asymmetric oblique and segmented rift models display many structural similarities to the segmented rifts of the Central and Northern North Sea rifts as well as to those in the Northern Ethiopian rift system, and in the Gulf of Suez, Egypt.