Imaging the seismic LAB and deeper asthenospheric low-velocity layers in the Ibero-Maghrebian region

Abstract

We present a new lithosphere-asthenosphere boundary (LAB) depth map of Iberia and adjacent areas built using ∼34500 Sp receiver functions from 998 broadband seismic stations, alongside an updated Ps-derived crustal thickness map of Iberia. We found an overall shallow LAB, with a minimum depth of 70-80km in areas of Cenozoic extension such as the eastern coast of Iberia and the Gibraltar-Alboran subduction back-arc, as well as in the Massif Central and the tectonically stable northwest of Iberia. LAB depths from 90km to 110km were only found within the areas of thickened crust in north-central Iberia and bordering the Gulf of Cádiz. The much deeper (150-180km) oceanic LAB of the Gibraltar-Alboran slab was also imaged in the western Gibraltar Arc. Sublithospheric negative-velocity gradients (NVG) in the 110-140km depth range are widespread in the back-arc of the Gibraltar-Alboran subduction system and in north-central Iberia, picturing a layered asthenospheric structure. In the Gibraltar Arc, the detachment of the slab through the subduction-transform edge propagator fault in the eastern Betics seems linked to the formation of the NVG, which are limited to the north by this structure.