Tectonic adaptation of the External Zones around the curved core of an orogen: the Gibraltar Arc

Abstract

There is no real curvature in the External Zones of the Arc of Gibraltar. These External Zones are made up by the juxtaposition of segments with NNW-SSE- or E-W-trending structures. Juxtaposition does not result from late tectonics nor from a paleogeographic layout, but only from Miocene tectonics. During and after the late Burdigalian, relative motion between Europe and Africa was essentially a N-S convergence which accounts for the E-W structural trends. The NNW-SSE trends are the result of offset of the two main plates along sinistral strike-slip fault zones that cross-cut the previously mobile block of the Internal Zones and that shifted southward through time. To explain the sharp juxtaposition of different trending structures, two tectonic stages must be considered in each area of the External Rif. During the first one the rocks behaved plastically while during the second they could only move as a block. The Internal Zones (Alboran block) slid independently between Europe and Africa only until early Burdigalian. After this time, they were locked in the main plates and broken together with them to allow further displacements.