Exhumation during a continental collision inferred from the tectonometamorphic evolution of the Alpujarride Complex in the central Betics (Alboran Domain, SE Spain)

The tectonometamorphic evolution of the Alpujarride Complex within the internal zones of the Betics reveals a complex structural and metamorphic succession of continental collision, synmetamorphic exhumation, nappe forming in the final stage of exhumation, and rifling. A complex tectonic evolution is deduced front the superposition of structures observed in several Alpujarride units of the central Betics together with their metamorphic record. The following sequence of events is suggested: (1) A first stacking event (D-1) is deduced from the presence of pre-St high-pressure-low-temperature metamorphic assemblages, (2) The synmetamorphic exhumation is inferred from the almost isothermal decompression pressure-temperature paths during which the S-2 main foliation developed; the condensation of the mineral zones perpendicularly to the S-2 foliation suggests large-scale vertical shortening during event D-2, (3) A new stacking event (D-3) is inferred from post-metamorphic thrusts and nappes, which are probably associated with kilometer-scale recumbent folds affecting the St main foliation, (4) A thinning event (D-4), revealed by extensional fault systems, is associated with crustal spreading on the concave side of the Gibraltar Arc, which resulted in the opening of the Alboran Basin from the early Miocene (Burdigalian), (5) From late Tortonian to Pliocene a continuous N-S to NW-SE compression took place (D-5). Stratigraphic, paleontological, and geochronological data suggest that event D-3 could be lower Miocene in age (Aquitanian): consequently, event D-1 and D-2 would be pre-Miocene.