Crust-mantle structures and Neogene-Quaternary magmatism in Italy

After the Middle Miocene, the Tyrrhenian-Apennine region is considered a kinematically closed system. Geodynamic forces were only local, and large lateral motions, induced by plate dynamics, were absent. During the last 10 Ma these forces transformed a segment of the Alpine-Adriatic collisional belt into a deep basin and into a new mountain chain. From the analysis of geophysical and geological data we infer that mantle upwelling above a deep-seated thermal plume caused this tectonic �revolution�. Support to this geological occurrence is given by the proposed presence of a 5 to 20 km-thick layer of dense magma (a soft mantle wedge, or mantle cushion) that underplates the western part of the Apennine range. This layer has contributed to the accretion of a new continental crust � an example of physical and chemical growing. The magmatic composition and the volcano-tectonic evolution indicate a tectonic rift environment and the transformation of the lithosphere mantle and crust, by a thermal anomaly and by fluid supply from deep mantle sources. In this model the high potash �Mediterranean� volcanism corresponds to the area underplated by mantle-derived material. New geophysical data acquired across the Tuscan geothermal province support this model.