Structural and kinematic constraints to the exhumation of the Alpujarride Complex (Central Betic Cordillera, Spain)

摘要

The polymetamorphic Alpujarride nappe Complex is one of the main constituents of the internal zones of the Alpine Betic-Rif chain. Still under debate are the tectonic processes involved in exhumation of its deep-seated portions, metamorphosed under high-pressure conditions during the Alpine crustal thickening. A systematic study of the exhumation-related ductile and brittle fabric observed in the different Alpujarride units reveals, independently from the metamorphic grade and age of the protoliths, a common sequence of deformation events. It involves early progressive top-to-the-N/NE ductile shearing, followed by a major top-to-the-N post-metamorphic extensional faulting event, which produced a complex re-organisation of the whole nappe pile. We propose that ductile exhumation of the deep-seated Alpujarride nappe piles was mainly completed before the onset of the post-orogenic extensional processes associated with the Early Miocene Alboran rifting. A switch from an early ductile underthrusting regime (Paleogene in age) to semibrittle-to-brittle extension (Early Miocene onward) is here proposed as responsible for the exhumation history of the Alpujarride Complex.