The Gibraltar arc, which closes the westernmost part of the Mediterranean basin, is a Miocene A-type subduction arc formed by the continental collision of various pre-Miocene terranes in the major zone of collision between the Iberian and African cratons. The hanging-wall block, known as the Albor¿n domain, has undergone more than 300 km migration from a more easterly position, where it was the continuation of the Alpine Cretaceous-Paleogene orogen. Contemporaneous with thin-skinned thrusting in the footwall, the Albor¿n domain underwent two episodes of nearly orthogonal extension in which extensional systems developed with directions of extension varying from a 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 chocolate tablet megastructure. This extensional pattern is not satisfactorily explained in previously proposed models for the evolution of the arc. Orthogonal extension is plausible in a process of the gravitational collapse of an overthickened crust; nevertheless, orogen-parallel extension is more difficult to explain in this context. We advocate that the WSW directed low-angle normal faults formed during large-scale extension in connection with important westward arc migration. The driving force of extension in a general context of convergence is controversial and varies between a convective removal model and a delamination model. Constraints on both the timing and the kinematics of extension, as presented in this paper, seem to support the contribution of both mechanisms. Convective removal may have started the process, but continued N-S convergence could have resulted in westward tectonic escape and asymmetric lateral inflow of asthenospheric material accompanying lithospheric delamination.¿ 1997 American Geophysical Union