Continental collision, crustal thinning and nappe forming during the pre-Miocene evolution of the Alpujarride Complex (Alboran Domain, Betics)

The tectono-metamorphic evolution of the Alpujarride Complex within the internal zones of the Gibraltar Arc indicates that the Alboran Crustal Domain underwent several contractional and extensional events. The superposition of structures and the metamorphic evolution observed in the Alpujarride Complex, and in particular in the Adra unit, suggest that these events are as follows: (a) the first thickening event (D1) results from continental subduction, and is evidenced by the presence of pre-S2 high-pressure mineral relicts; (b) the thinning and associated vertical shortening event (D2) is indicated by an almost isothermal decompression during which the S2 main foliation developed; (c) kilometric-scale N-vergent recumbent folds of the condensed metamorphic sequences, and thrust and nappe-forming in the Alpujarride Complex, suggest that a second thickening event (D3) took place; (d) the second thinning event (D4), which affects the whole Alboran Domain, is evidenced by extensional fault systems resulting in the opening of the Alboran Sea. The oldest synrift deposits are of the Late Oligocene and Early Miocene, suggesting that D1 to D3 events are pre-Miocene; and (e) from the Late Tortonian to the Pliocene, the extensional systems were folded due to a continuous N-S to NW-SE compression.