Late stage of the Gibraltar arc subduction system (western Mediterranean): from slab-tearing to continental-edge delamination

The Gibraltar arc subduction system is the result of the fast westward roll-back of the Alboran slab at the westernmost end of the Mediterranean Sea. This westward motion is controlled, at its northern edge, by slab tearing along a so called STEP (Subduction-Transform-Edge-Propagator) fault under the Betics orogen. The Alboran subduction process is in its last evolutionary stage, where the oceanic lithosphere has been fully consumed and the continental lithosphere attached to it collides with the overriding plate. In this situation the continued slow convergence between Iberia and Africa could lead to a short stage of continental subduction. However, the particular setup after slab tearing, characterized by a sharp lateral contrast between the orogenic Betic lithosphere and the adjacent thinned lithosphere of the overriding Alboran domain, is also prone to trigger continental delamination, i.e. the detachment between the crust and the lithospheric mantle. Several lines of evidence indicate that northwards mantle delamination is likely occurring in the central Betics. The fast average topographic uplift during the last 8 Ma together with the lack of spatial correspondence between the highest topography (Sierra Nevada Mountains) and the thickest crust indicate that the topography could be partly supported by asthenospheric upwelling due to continental delamination. In this study we take advantage of an unprecedented resolution seismic receiver functions lithospheric mapping in the Betic orogen to investigate the conditions for, and consequences of, edge delamination in the Iberian margin after slab tearing. We show that given a weak enough Iberian lower crust the delaminated lithospheric mantle peels off the crust and adopts a geometry consistent with the imaged southward dipping Iberian lithosphere in the central Betics. In contrast, the thinned lower crust beneath the Iberian margin in the eastern Betics prevented mantle delamination via asthenospheric inflow into the lower crust.