EVIDENCE FOR THE EASTWARD MIGRATION OF THE ALBORAN SEA BASED ON REGIONAL SUBSIDENCE ANALYSIS - A CASE FOR BASIN FORMATION BY DELAMINATION OF THE SUBCRUSTAL LITHOSPHERE

The paradox of an extensional basin forming at a site of colliding con tinents is apparent in the evolution of the Neogene Alboran Sea basin of the westernmost Mediterranean. Processes that may be responsible fo r such basins forming at sites of continental collision include subduc tion and the removal of subcrustal lithosphere by either convection (e xtensional collapse) or delamination and have recently been invoked to explain the formation of the Alboran Sea basin. Decoupling of the the rmal boundary layer can reverse the stress field from a state of compr ession to one of extension. The processes of extensional collapse and delamination involve removal of this layer and would have similar cons equences in terms of modifying lithosphere geometry: replacement of th e detached thermal boundary layer by hot asthenospheric material, whic h would produce a high geothermal gradient and in turn cause uplift at the surface. With identical effects, it is difficult to distinguish b etween the two mechanisms. Using the technique of backstripping, a sub sidence history which evidences the coexistence of subsided and uplift ed areas in the Alboran Sea basin through the Miocene to the Quaternar y, has been reconstructed for the basin. While the deformation front o f the Alboran Domain migrated westward, subsidence in the Alboran Sea basin propagated in the opposite sense, east/southeastward. This is be st explained as the basin forming above a southeastward-propagating, d elaminating subcrustal lithospheric slab,