Shallow Asthenospheric Volumes Beneath Cenozoic Volcanic Provinces in the Circum-Mediterranean: Evidence from Seismic Tomography, Magmatic Geochemistry and Integrated Geophysical-Petrological Thermochemical Modelling

To relate Intraplate volcanism to upper mantle structure, we investigate small-scale structural-variations of the lithosphere-asthenosphere beneath the Circum-Mediterranean using regional high-resolution 3-D surface-wave tomography. The imaged low shear-wave velocities (Vs<4.2 km/s) between depths of ~70-300 km indicate the presence of nine shallow asthenospheric volumes (SAVs) across the Circum-Mediterranean upper mantle forming a partly interconnected belt and separated only by high velocity slabs and thickened lithosphere. Integrated geophysical-petrological modelling for 14 representative locations, yields estimates of the lithospheric thickness and the upper mantle geotherm and confirms the presence of thin lithosphere (<80 km) above areas of anomalously warm SAVs (>1300°C).

We distinguish between Intraplate, Mixed-origin and Subduction-related volcanism in the Circum-Mediterranean during the last 70 Ma and find a remarkable colocation between the SAVs and Cenozoic Intraplate and Mixed-origin volcanic provinces (IMVPs). Moreover, the lateral distance from any shallow asthenosphere to the closest neighboring volcanic province is, on average, as low as 100 km, with a maximum distance of 350 km, indicating a dense network of IMVPs above SAVs. By contrast, IMVPs are completely absent in areas of thick mantle lithosphere.

We relate origin of the SAVs either to asthenospheric upwelling caused by slab-rollback and back-arc extension (Aegean-Anatolian, Pannonian, Moesian, Western Mediterranean SAVs) or to thermal erosion of the lithosphere partly coupled with continental rifting (Adriatic, Central European, North African, Middle East SAVs), respectively. The oldest ages of the IMVPs in the Circum-Mediterranean indicate that the development of the current SAVs started at about ~60-70 Ma ago and accelerated in Neogene.