Role of décollement material with different rheological properties in the structure of the Aljibe thrust imbricate (Flysch Trough, Gibraltar Arc): an analogue modelling approach

The Miocene Aljibe thrust imbricate (Flysch Trough), in the external zone of the Gibraltar Arc, shows large changes in structural style towards the foreland. Rheological variation of the décollement rocks—Triassic evaporitic rocks and Mesozoic limestones—appears to be the main factor controlling the contrasts in structural style that characterise adjacent wedge domains. In order to test this hypothesis, we carried out analogue experiments involving three-dimensional variations of décollement material. A plate of viscous material was placed in the central part of the models, at the base of the sand multilayers. Different geometries of the viscous plate were used. Experimental results show a strong link between the rheological properties of the décollement material and the structure of the overlying thrust wedge. These results compare well with the internal geometry and vergence distribution in the Aljibe thrust imbricate. Indeed, the tectonic style of the wedge can be explained as a consequence of variations of rock type along the basal décollement.