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Based on a revision of stratigraphic and structural data relative to the Balearic basin, the Corsica‐Sardinia massif, the Northern Tyrrhenian Sea and the Northern Apennines the following new hypothesis is proposed for the area located between the Sardinian‐Corsican‐Provençal and Northern Apennines regions: (a) convergence with subduction of oceanic crust under the Iberian plate beginning in the Late Cretaceous; (b) continental collision in the Oligocene‐Aquitanian, with development of the Northern Apennines belt and transpressive deformation in a hinterland that consisted of the Corsica‐Sardinia massif (still attached to the Iberian plate); (c) in the Burdigalian the tectonic regime changed from compressive to extensional. During this period the Corsica‐Sardinia massif migrated contemporaneously with opening of the Balearic basin, the Sardinian rift, and the Northern Tyrrhenian sea; (d) from the Burdigalian to the present, there was contemporaneous compression at the front and extension at the back of the Northern Apennines chain; both these features progressively migrated toward the east. The coeval extension and compression is attributed to lithospheric delamination toward the external part of the belt.

The Larderello geothermal field is located in the Inner Northern Apennines, in an area which has been subject to extension since the Early Miocene. The latest extensional episode (Pliocene -Present) has resulted in the formation of NW-trending, NEdipping listric normal faults, whose geometry is controlled down to f 3 km by borehole data. In this paper, we integrate a new interpretation of seismic reflection lines with existing seismic, field, and borehole data to analyse the relations among listric normal faults, the top of the brittle -ductile transition, and the migration of geothermal fluids.In accordance with previous interpretations, we consider the strong reflector (K-horizon) marking the top of the reflective mid-lower crust, and located at a depth of 3 -5 km in the geothermal area, to represent the top of the brittle -ductile transition. Its reflectivity most probably derives from the presence of overpressured fluids. We identify three main NW-trending, NEdipping extensional brittle shear zones, showing listric geometry and soling out in the vicinity of the K-horizon. The latter appears to be dislocated in correspondence of the soling out of the shear zones. These shear zones, because of the associated intense fracturing, represent the most natural channels of upward migration of geothermal fluids from the magmatic sources located below the K-horizon.We suggest that these two conclusions-that listric normal faults root at or near the brittle -ductile transition, and that they act as preferential upward migration paths for magmatic fluids-may be of general validity for geothermal fields located in extensional settings. D

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