3D evolution of a pop-up structure above a double basement strike-slip fault: Some insights from analogue modelling

In analogue modelling, pop-up structures have previously only been described in models of basement-involved strike-slip deformation with a stepover or restraining bend configuration. We describe the results of an analogue experiment with an alternative model configuration to investigate the structural development of pop-up structures. This model consists of a cover sequence of sand overlying two parallel running basement faults, which experience the same sense and the same amount of slip during deformation. The ratio of basement fault separation (1 cm) to overburden thickness (4 cm) is small. The experiment has been recorded in an X-ray tomograph, by which it was possible to investigate the 3D structural evolution of the model. During deformation, an elongated rhombic pop-up structure developed centrally above the basement faults. The faults bounding the pop-up structure displayed convex-upward as well as straight to concave-upward shapes. During deformation the topography above the basement faults increased to a maximum of c. 4.8 mm, compared to a maximum subsidence of c. 1.5 mm on both sides of the basement faults. During progressive deformation, local maximum horizontal principal stresses displayed a considerable rotation, from 45° in the initial stages, to (sub)parallel in a more advanced stage and finally back to c. 45° to the strike of the basement faults.