THE ROLE OF EXTENSION IN THE MIOCENE DENUDATION OF THE NEVADO-FILABRIDE COMPLEX, BETIC CORDILLERA (SE SPAIN)

The Internal Zone of the Betic Cordillera, SE Spain, consists of a nap pe stack of three complexes, the deepest of which is the Nevado-Filabr ide Complex. The zone is separated from the overlying Alpujarride Comp lex by a crustal scale shear zone that has variously been interpreted as a thrust or an extensional detachment. A suite of 74 new apatite an d zircon fission track results have been obtained from the Nevado-Fila bride Complex and these have been used to define regional cooling patt erns for the complex. Rapid cooling (105 degrees C-200 degrees C Ma(-1 )) is spatially related to the tectonic contact with the overlying Alp ujarride Complex. Cooling to near-surface temperatures occurred first in the east (Sierra de los Filabres) during the mid-Serravallian (12+/ -1 Ma) and was completed by the early Tortonian (9-8 Ma) in the west ( Sierra Nevada). There is no correlation between fission track age and sample elevation. These results are consistent with tectonic unroofing of this complex, a finding that favors extension as the mechanism by which the two complexes were brought into contact. Extension spans the middle and earliest upper Miocene (12-8 Ma) in the study area and the refore lasted much longer than previously documented. A hypothesis is advanced which links oblique convergence between the Iberian plate and the Betic internal Zones, resulting in crustal contraction at depth, with orogen parallel extension in the middle and upper crust.