A Geological History for the Alboran Sea Region

Abstract

The Alboran Basin is a Neogene-Quaternary extensional basin located within the Betic-Rif alpine cordillera. The region where the current basin is located holds great oceanographic relevance, as it lies in the area of connection between the western (Atlantic Ocean basin) and eastern seas (ocean basins of the Ligurian Tethys and then Western Mediterranean Sea) of Iberia. The extensional collapse of the Eocene Alpine orogen led to the crustal thinning and formation of the Western Mediterranean basin and the splitting of lithospheric fragments, the Alboran Domain among them, along its margins. The N-S convergence of the African and Eurasian plates, together with the westward escape of the Alboran Domain and its extensional tectonics in the back-arc region linked to the retreat of a subduction zone northwestward has determined the basin’s formation and evolution since the upper Oligocene to Tortonian times. The stretching of the continental crust produced its configuration, creating several sub-basins and tectonic highs, and was accompanied by an important magmatic phase that peaked in the middle-late Miocene. The direction of African-Eurasian convergence evolved to NW-SE in the late Tortonian and is presently WNW-ESE, producing an inversion of the basin in its interior, with the uplift of main reliefs (e.g., the Alboran Ridge), and a progressive elevation of adjacent mountain ranges in southern Iberia (Betic) and northern Africa (Rif), substantially reducing the basin’s width. During this phase, convergence is resolved with an indentation tectonic model in the central Alboran Sea; and to accommodate this deformation, two conjugated sets of dextral WNW-ESE and sinistral NE-SW to NNE-SSW faults are generated. The sedimentary infill of the Alboran Basin consists of unconformable Miocene to Quaternary deposits controlled by the tectonic deformation and paleoceanography. Two important events marked the sedimentary evolution: Messinian desiccation and the opening of the Strait of Gibraltar