Superposition of extensional detachments during the Neogene in the internal zones of the Betic cordilleras

Abstract

In the internal zones of the Betic cordilleras, extensional structures have developed from the Upper Oligocene to the present day; they are contemporaneous with compressional structures (folds and thrusts) in the external zones. From the Upper Oligocene to the Aquitanian, extension occurred in the Malaguide/Alpujarride detachment, and related structures show varying kinematics in different sectors. Younger deformations with a top-to-the-N sense of movement have affected Nevado-Filabride (ductile shear zones), Alpujarride (ductile and brittle shear zones) and Malaguide rocks (normal faults). At least from the Late Burdigalian up to the Lower Tortonian, displacements have occurred in the Alpujarride/Nevado-Filabride detachment. Deformations have been generally non-coaxial, with a top-to-the-W sense of movement. Stretching lineation trends in the Nevado-Filabride rocks curve from E to W suggesting a progressive variation of the ductile-shear-zone kinematics related to the Alpujarride/Nevado-Filabride detachment between the Aquitanian and Lower Tortonian stages. Deformations from the Lower Tortonian to the present day are normal faults, formed in extensional settings in the upper part of the crust, and folds and strike-slip faults which indicate N-S to NNW-SSE shortening directions and E-W to ENE-WSW extension directions.