Deep electrical resistivity structure of the northern Gibraltar Arc (western Mediterranean): evidence of lithospheric slab break-off

P>Uncertainties about the lithospheric structure of the Gibraltar Arc have led to the proposal of several contradictory models to explain its geodynamic setting. Herein, we present a novel 3-D model of the lithospheric electrical resistivity distribution beneath the whole Betic Cordillera obtained by inverting both broad-band and long-period magnetotelluric data. The lithosphere-asthenosphere boundary under SW Iberia is shown to be deeper than under the Alboran Basin. In addition, the sensitivity tests confirm the presence of a N-S oriented low-resistivity anomaly at lithospheric mantle depths east of the 4 degrees W meridian. It coincides with an area of low velocities without earthquake hypocenters and is interpreted as asthenospheric material intruded by the lateral lithospheric tearing and breaking-off of the E-directed subducting Ligurian slab under the Alboran Domain. This scenario suggests that the opening of the Alboran Basin is related to the westward rollback of this E-directed subducting slab.