Exhumation of high-pressure metapelites and coeval crustal extension in the Alpujarride complex (Betic Cordillera)

Abstract

The current configuration of the Alpujarride complex (Betic Orogen) comprises a stack of thinned tectonic units, made up mainly of continental crust. P-T path modelling in different levels of an Alpujarride unit (the Salobreña tectonic unit) reveals a high-pressure metamorphic stage followed by subsequent decompression at nearly isothermal conditions. Nevertheless, the P-T conditions differ from one level to another: while the top of the Permo-Triassic metapelites includes carpholite-kyanite-bearing assemblages (10 kbar/425°C), intermediate levels are characterized by Mg-rich chloritoid-Zn-rich staurolite-kyanite-bearing assemblages (minimum 10.5 kbar/450°C) and the bottom of the Palaeozoic metapelite sequence presents garnet-kyanite-plagioclase-bearing assemblages (average conditions of 13 kbar/625°C). Thus, the Salobreña tectonic unit represents an entire upper continental segment containing several crustal layers which underwent high-pressure metamorphism during Alpine continental subduction. The decompression, associated with an important mineral growth stage and the development of flat-lying regional foliation, reflects the thinning of this crustal segment, which resulted in parallel disposition of the bedding and metamorphic zones. At low-pressure conditions, large-scale folds affect the regional foliation, producing stratigraphic duplication, metamorphic inversions and the general reorganization of previous Alpujarride sheets. Finally, brittle Miocene extensional tectonics, coeval with the generation of the Alboran Basin, contributed to the definitive exhumation of the Alpujarride complex.