Neogene extensional collapse in the western Mediterranean (Betic-Rif Alpine orogenic belt): Implications for the genesis of the Gilbraltar Arc and magmatic activity

The Betic-Rif orogenic belt crops out in the western Mediterranean and constitutes the westernmost part of the Alpine edifice. The building up of this belt by compressional nappe tectonics occured during a series of Alpine deformational episodes. Subsequent Neogene extension resulted from the collapse of the previous compressional edifice through major extensional detachment systems. This episode was accompanied by cafe-alkaline to shoshonitic and lamproitic volcanism, tectonic denudation of metamorphic core complexes, and emplacement of peridotite bodies as a final consequence of the evolution of detachment systems. Furthermore, we relate the generation of the Gibraltar Arc and the opening of the Alboran Sea to this major extensional event. Finally, two main stages of tectonic denudation of these detachment systems are defined: (1) Nevado Filabride stage, with ex-humation of metamorphic core complexes, and (2) Ronda-Beni Boussera stage, with a more advanced degree of denudation, leading to the exhumation of upper mantle peridotites, which may be tentatively termed mantle core complexes.