The lithospheric extension affecting the Tuscan-Tyrrhenian domain represents one 
of the most relevant and recent tectonic processes within the entire Alpine-
Mediterranean deformation area. The heat input from the mantle is responsible for 
the presence of  large geothermal resources at accessible depths in the crust, as 
testified by temperature and heat flow anomalies, locally extremely high. Despite 
intensive exploration and exploitation drilling programs carried out in Tuscany, 
mainly since the 70s, the nature, physical properties and structure of the 
intermediate and lower crust and of the upper mantle are still debated. The 
available dataset for the Tuscan area was significantly improved by the acquisition 
of the deep crustal seismic reflection profiles (CROP Profiles), in the mid 90s. 
The profiles CROP 18A and 18B, crossing NW-SE wards the Larderello and Monte Amiata 
geothermal fields, and the CROP 03 profile, intersecting with W-E direction the 
CROP 18B, were recently reprocessed to better characterize the crustal and upper 
mantle structures of the entire Tuscan geothermal area. The results show new 
remarkable and interesting features, i.e.: the presence of extensional structures 
below the “K Horizon” regional high-amplitude discontinuous reflector; a second 
deeper and more continuous similar horizon; mantle intrusions; strong reflectors in 
the lower crust and a discontinuous crust/mantle transition with possible 
underplating. Accurate analyses of the seismic attributes suggest the presence of 
fluids/melts from the “K Horizon” down to about 10 km depth. 
These new data were put into a simple and conceptual 2-D model, aimed to provide a 
set of preliminary thermal models, to be compared with the experimental borehole 
temperature and heat flow data. The 2-D numerical modelling followed a two-steps 
process: first, modelling the regional conductive heat transfer in the upper 10-12 
km of the crust and, secondly, superimposing  local advection, in correspondence of 
the geothermal fields. The 2-D regional conductive model was realized by means of a 
steady-state forward simulation, under the assumption of a purely conductive heat 
transfer. The unknowns are the basal heat flow and the thermal properties of the 
crustal rocks, whereas the results are the temperature distribution with depth and 
the surface heat flow.  To account for the uncertainties in the physical properties 
of the crustal rocks we produced two sets of models, using the parameters and 
assumptions which maximise and minimise, respectively, the surface heat flow output 
to be compared with the experimental data. Local heat transfer by advection was 
introduced in the upper crustal structures of the geothermal fields, where the CROP 
seismic profiles were indicating presence of fluids. The temperature, depth and 
extension of these reservoirs can explain most of the present extremely high 
surface heat flow anomalies.

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