Abstract

The external wedge of the Gibraltar Arc orogenic system (western Mediterranean) is a natural case of a fold-and-thrust salient. Although at the scale of the arc a swing of the structural trend can be observed, the presence of closed, crescent-like structures, some of them more than 25 km long and scattered over an area of 3500 km2, characterize the Gibraltar Arc external wedge. This feature makes it very different from a ‘classical’ arc-shaped fold-and-thrust belt. Detailed structural maps of representative crescent-like structures are presented. Synorogenic sediments reveal that they probably formed during a short time interval, most probably during a single shortening event. The crescent-like structures are localized in front of a recess formed by the internal zones that acted as backstop. This backstop shape and a viscous substrate (essentially Triassic evaporites below the fold-and-thrust external wedge) constrain the experimental setting of an analogue model in which we were able to reproduce structures that developed originally with a highly non-cylindrical shape during a single, straight convergence. Moreover, the tectonic transport directions along the thrusts are broadly comparable in the natural case and the model.

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