The Internal Zone of the Betic Cordillera, SE Spain, consists of a nappe stack of three complexes, the deepest of which is the Nevado-Fil¿bride Complex. The zone is separated from the overlying Alpuj¿rride Complex by a crustal scale shear zone that has variously been interpreted as a thrust or an extensional detachment. A suite of 74 new apatite and zircon fission track results have been obtained from the Nevado-Fil¿bride Complex and these have been used to define regional cooling patterns for the complex. Rapid cooling (105 ¿C--200 ¿C Ma-1) is spatially related to the tectonic contact with the overlying Alpuj¿rride 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 therefore 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.¿ 1997 American Geophysical Union