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 th ickening 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 moveme nt. The present-day Alpujarride-Nevado-Filabride contact is a detachme nt fault generated in this shearing regime. In the footwall, the first structure developed in this extensional stage is a planar-linear fabr ic characterized by constrictive strain, that is axial planar to kilom etric recumbent tight to isoclinal folds. The planar-linear fabric is folded by inclined close to open folds with axes parallel to the stret ching lineation. The planar-linear fabric and folds are deformed by a late extensional crenulation cleavage near the detachment surface. Fin ally, brittle deformation was generated within the same kinematic fram ework as that of the ductile structures. In the hanging wall, meanwhil e, deformation had a brittle character producing faults and joints.