The Thermal Structure of the Upper Crust in Central-Southern Italy and its Correlation with the Distribution of Geothermal Resources

Temperature is a key parameter in controlling the in-situ petrophysical properties, the solid and fluid phase equilibria, the stress-strain relationships as well as the occurrence and potential of geothermal resources. Thermal field anomalies are determined by a great number of different factors and the study of their nature together with a quantitative appraisal are critical in mapping the spatial distribution of the conventional and unconventional geothermal resources as well as estimating the deep crustal conditions and their lateral variability. With the aim to study the thermal structure of the upper crustal levels in Central-Southern Italy, we exploited lithostratigraphic, hydrological, petrophysical and geophysical data. We described the main heat transport phenomena occurring in the upper crust and we applied these concepts to a numerical modelling approach. We developed a new 3D geological model considering the main lithothermal units acting as the cap-rock of the deep-seated hydrothermal systems, the regional carbonate reservoirs and the crystalline/metamorphic basement. The temperature data from the accessible deep boreholes represented the main thermal constraints of the models. The maximum logged depth is about 7 km, although the majority of the data distributes in the depth range 1.5-3.5 km. At greater depths, seismological and rheological evidence (i.e. the thickness of the seismogenic layer) gave us further indirect information regarding the deep thermal state of the upper crust. Along the Apennine chain, particularly in correspondence of outcropping carbonate units, the temperature distribution is affected by downward heat advection. The most favourable geological conditions leading to the development of high temperature hydrothermal systems occur far from the outcropping carbonate units; especially in the Tyrrhenian side of the peninsula affected by crustal stretching and Plio-Pleistocene magmatic activity.