Geothermal Anomalies and Structural Features of Southern Tuscany (Italy)

Abstract

The reconstruction of the geothermal situation in southern Tuscany is updated from a series of integrative geophysical investigations carried out over the past few years and from the analysis of almost 500 thermal measurements points (shallow gradient and deep boreholes). All of Tuscany is characterized by thermal gradient (G>50oC/km) and heat flow density (HF) (q>100 mW/m2) positive anomalies that decrease eastwards along the Elsa-Siena grabens. Three thermal anomalies of minor extent and intensity have been found outside the well known geothermal areas and could represent the continuation of the two main anomaoies of LarderellopTravale and Mt. Amiata, circumscribed by the isoflow line of 200 mW/m2. Two of theses anomalies are situated south of Larderello -Travale, while the most extensive is west of Mt. Amiata. The deep HF has also been defined within the limits of the geothermal fields under exploitation, in order to evaluate any difference with respect to raised surface values caused by shallow convective circulation. The HF anomalies of Larderello-Travale and Mt. Amiata correspond to structural and geophysical anomalies, which corroborate the hypothesis that extensive deep intrusive bodies produce the thermal anomalies.