Constraints on Moho Depth and Crustal Thickness in the Liguro-Provençal Basin from a 3d Gravity Inversion : Geodynamic Implications

Abstract

3D gravity modelling is combined with seismic refraction and reflection data to constrain a new Moho depth map in the Liguro-Provencal Basin (Western Mediterranean Sea). At seismically controlled points, the misfit between the gravimetric solution and the seismic data is about 2 km for a range of Moho depth between 12 km (deep basin) and 30 km (mainlands). The oceanic crust thickness in the deep basin (5 km) is smaller than the average oceanic crust thickness reported in open oceans (7 km), pointing to a potential mantle temperature 30°C to 50°C below normal and/or very slow oceanic spreading rate. Oceanic crust thickness is decreasing towards the Ligurian Sea and towards the continent-ocean boundary to values as small as 2 km. Poor magma supply is a result of low potential mantle temperature at depth, lateral thermal conduction towards unextended continental margin, and decrease of the oceanic spreading rate close to the pole of opening in the Ligurian Sea. Re-examination of magnetic data (paleomagnetic data and magnetic lineations) indicates that opening of the Liguro-Provencal Basin may have ceased as late as Late Burdigalian (16. 5 Ma) or even later. The absence of significant time gap between cessation of opening in the Liguro-Provencal Basin and rifting of the Tyrrhenian domain favours a continuous extension mechanism since Upper Oligocene driven by the African trench retreat.