MODE OF EXTENSIONAL TECTONICS IN THE SOUTHEASTERN BETICS (SE SPAIN) -IMPLICATIONS FOR THE TECTONIC EVOLUTION OF THE PERI-ALBORAN OROGENIC SYSTEM

The Gibraltar are, which closes the westernmost part of the Mediterran ean basin, is a Miocene A-type subduction are formed by the continenta l collision of various pre-Miocene terranes in the major zone of colli sion between the Iberian and African cratons. The hanging-wall block, known as the Alboran domain, has undergone more than 300 km migration from a more easterly position, where it was the continuation of the Al pine Cretaceous-Paleogene orogen. Contemporaneous with thin-skinned th rusting in the footwall, the Alboran domain underwent two episodes of nearly extension in which extensional orthogonal developed with direct ions of extension NNW-SSE system, orthogonal to the belt axis, in the late Burdigalian-Langhian to a WSW directed orogen-parallel one in the Serravallian. The superposition of these two systems resulted in a ch ocolate tablet megastructure. This extensional pattern is not satisfac torily explained in previously proposed models for the evolution of th e are. Orthogonal extension is plausible in a process of the gravitati onal collapse of an overthickened crust; nevertheless, orogen-parallel extension is more difficult to explain in this context. We advocate t hat the WSW directed low-angle normal faults formed during large-scale extension in connection with important westward are migration. The dr iving force of extension in a general context of convergence is contro versial and varies between a removal model and a delamination model. o n both the timing and the kinematics of extension, as presented in thi s paper, seem to support the contribution of both mechanisms. Convecti ve removal may have started the process, but continued N-S convergence could have resulted in westward tectonic escape and asymmetric latera l inflow of asthenospheric material accompanying lithospheric delamina tion.