Sur un modèle explicatif de l'arc de Gibraltar

Many authors have explained the Gibraltar arc in various manners. It is our purpose to set up an explanation which takes into account the recent geological discoveries about the Geology of this region, and the concept of Plate Tectonics. Stratigraphic, metamorphic and structural arguments support the fundamental opposition between internal and external zones in the Betic-Rif mountain system. Internal zones, clearly showing an arcuate structure, were built before Miocene. External zones, on the contrary, were folded mainly during Middle Miocene. Both zones have been involved in important shortening (with strike-slip faulting) just before Messinian (late Miocene). Taking into account the later deformations, we can assume that the internal zones constituted, at the beginning of the Miocene, the sub-plate of Alboran, which separated, eastwards from the Azores transform-fault, the European and African plates. According to this model, we can suppose the Alboran sub-plate to be fixed, whereas the European and African plates move eastwards. So, tectonic structures oblique to the direction of drift, like folds and thrusts along a transcurrent-fault, appear along the north-western and south-western margins of the Alboran sub-plate; along its western margin, N-S structures form, thrusting towards the west. Our geometrical model is able to account for peculiar and unexplained structures of this region. Because of its simplicity, we are conscious of the limits of our explanation, but it seems to us to be a valuable working hypothesis, which needs further geophysical and geological tests.