The metamorphic and structural evolution of the Alpujarride Complex - Internal Zone, Betic Cordillera (S. Spain)

The Metamorphic and Structural Evolution of the Alpujarride Complex - Internal Zone - Betic Cordillera (S Spain) Metamorphosed pelitic schists within the Alpujarride Complex - a component of the Internal Zones of the Betic Cordillera, southern Spain - have experienced a complex metamorphic/structural evolution, most recently during an Alpine-age orogenic event. Preservation of disequilibrium textures permits an insight into the metamorphic conditions during the formation of structural fabrics. Metamorphic grade in the area varies from sillimanite grade to chlorite grade. Rocks in the area (50 km south of Granada) have been affected by at least three phases of ductile deformation. The two most recent fabrics, Ss and St, are both crenulation cleavages; widespread examples occur which demonstrate the superposition of St on to Ss. Ductile/brittle normal faults developed during and after both phases of ductile deformation. The Dt phase of deformation generates kilometre-scale folds, the inverted limbs of which overturn the metamorphic sequence related to the Ds deformation and fault contacts that developed during and after the Ds deformation, but prior to Dt. High grade rocks are apparently structurally above low grade rocks in the overturned limbs of Dt folds. Trajectories in P-T space for rocks of different metamorphic grades, constrained from mineral relations with the regional foliations Ss and St and the application of thermobarometric techniques to appropriate assemblages, show that the Ss and St foliations developed during decompression, accompanied by heating. Peak metamorphic temperature occurred after the end of the Ds deformation event, and temperatures of above 550°C persisted to low pressure (3-4 kbar) conditions. Results from geochrology techniques - U-Pb, Ar-Ar on muscovite and biotite, and apatite fission track - yield ages that are within error of each other, indicating that the Alpujarride Complex experienced rapid cooling during decompression from around 19.2 Ma