Highlighting the crustal structure of southern Tuscany by the reprocessing of the CROP03 NVR profile

The formation of the Tyrrhenian basin and the formation and evolution of the Apennines are believed to be the consequence of the settlement of two mantle domes, one in the southern Tyrrhenian Sea and one in the Tuscan-Latium area. These domes are considered the result of the interaction between the pre-existing lithospheric mantle (and crust) and a thermal input in presence of fluids derived from deep mantle sources. A consequence is the peculiar structure of the crust which interacts with the uppermost mantle, in a region where extensional regime, crustal thinning and magma intrusions have been identified utilizing geophysical data, and in particular the reprocessing of reflection seismic lines crossing an area where important geothermal fields have been exploited. The new models were derived from heat-flow and gravity anomalies, deep seismic soundings, S-waves velocity models constructed by shallow and deep tomographic inversion and subsequent modelling of flow and stress distribution in the lithosphere, deep reflection lines (CROP profiles). The reprocessed section of the deep seismic profile CROP-03, in the sector from the Tyrrhenian shore to the Siena graben, puts in evidence important features, that are compared directly to the land profiles CROP-18A and -18B and to LISA lines acquired offshore, in the Tuscan archipelago. The high resolution of reflection seismic images, and the AVO analysis, highlight the lithology and physical properties of the crustal rocks of southern Tuscany. The intrusion of mantle-derived magmas and lithology differentiation inside the lower crust, the vertical channels corresponding to the ascent paths of magma from crust-mantle transition and fluids dominating the upper crust of southern Tuscany represent the source and motor of the geothermal resources.