Possible models of the deepest part of the Larderello geothermal field

The geological and geophysical data gathered so far at Larderello indicate the presence of a magmatic body, whose size, depth and volume are still a matter of debate. Granitic dikes as old 3.8-2.9 as Ma and a widespread contact aureole have been found in several wells. Heat flow data show positive anomalies, interpreted as the result of circulation of hot fluids above shallow magmatic bodies. The presence of low-density bodies is inferred by negative gravity values, often correlated with the positive heat flow anomalies. Reflection seismic surveys reveal the presence of a highly reflective horizon (named K) at a depth range of 3-12 km below the geothermal area; seismic tomography shows a low velocity body 30-40 km wide below the K horizon. Magnetotelluric surveys indicate the presence of a conductive body in good correlation with the other anomalies. These geophysical informations are used as "a priori" input data to test the reliability of various models: granite intrusion, geopressurized horizons below impervious layers, contact metamorphic aureole, listric faults or a combination of the four