The lithosphere–asthenosphere boundary in the western Mediterranean from 3D joint gravity and geoid modeling: tectonic implications

A new integrated three-dimensional (3D) gravity and geoid forward modeling was used to investigate the lithospheric structure of the northwestern Mediterranean basins, namely the Gulf of Lyons, Liguro-Provençal Basin, Valencia Trough, and South Balearic Basin. Available geological and geophysical data were used to construct preliminary maps of the thickness of the sediments and the base of the crust and lithosphere, which were further refined by 3D modeling. Our model results show that the base of the crust thins from 22 km in the SW areas of the Valencia Trough to less than 12 km at its NE transition to the oceanic domain of the Provençal Basin and from 28 km in the shelf area of the Gulf of Lyons to about 12 km in the deep oceanic part of the basin. Upper mantle densities vary from 3240 kg/m3 beneath the Valencia Trough (where P-wave velocities are anomalously low, suggesting the presence of an anomalous uppermost mantle), to 3320 kg/m3 beneath the Gulf of Lyons and the Provençal Basin, where ‘normal’ P-wave velocities are recorded. The base of the lithosphere rises from ∼75–80 km at the shoreline of the Valencia Trough and Gulf of Lyons to 60 km in the northern part of the Valencia Trough and 55–60 km at the center of the Provençal Basin. The structure of the crust and lithospheric mantle obtained from the 3D modeling indicates differential thinning. Moreover, other geophysical observations, e.g., the uneven distribution of heat flow values, suggest an asymmetric extensional model.