THE ALPUJARRIDE NEVADO-FIBABRIDE EXTENSIONAL SHEAR ZONE, BETIC-CORDILLERA, SE SPAIN

In the Betic Cordillera, the initial thickening of the Alboran Domain produced an Alpine high pressure-low temperature (HP-LT) metamorphism in the Alpujarride and Nevado-Filabride complexes. After 19 Ma this thickening process evolved to an extensional stage with uplift rates of between 1 and 2 mm year-1. The extensional stage generated structures in a heterogeneous shear regime with a top-to-the-west sense of movement. The present-day Alpujarride-Nevado-Filabride contact is a detachment fault generated in this shearing regime. In the footwall, the first structure developed in this extensional stage is a planar-linear fabric characterized by constrictive strain, that is axial planar to kilometric recumbent tight to isoclinal folds. The planar-linear fabric is folded by inclined close to open folds with axes parallel to the stretching lineation. The planar-linear fabric and folds are deformed by a late extensional crenulation cleavage near the detachment surface. Finally, brittle deformation was generated within the same kinematic framework as that of the ductile structures. In the hanging wall, meanwhile, deformation had a brittle character producing faults and joints.