The structural evolution of the Radicondoli–Volterra Basin (southern Tuscany, Italy): Relationships with magmatism and geothermal implications

• The Radicondoli–Volterra Basin in southern Tuscany evolved in a compressive regime.
• Magmatic intrusions of southern Tuscany area coeval with the compressive regime.
• Magmatic intrusions likely ascended along active or inactive thrust ramps.
• Ramps anticlines may represent future targets for geothermal researches.

The Western Tuscany, in the inner sector of the Northern Apennines, is characterized by a thinned continental crust (∼20–25 km), high heat flow (>100 mW m−2), and the presence of magmatism. The latter produces the current geothermal activity, which is mostly localized at the large Larderello–Travale field settled above the granites with the same name. These features and the several Late Miocene sedimentary basins that developed in the area are normally related to an extensional tectonics that affected the back-arc area since the Early-Middle Miocene (∼16 Ma), although, some geophysical studies image the continental crust deformed by W-dipping thrust faults. Here we present a new field survey conducted in the Radicondoli–Volterra Basin, which bounds the Larderello–Travale pluton system to the northeast. The results support former conclusions that the basin infill has been intensely shortened. Integrated analysis of other surrounding hinterland basins suggests that a phase of regional shortening affected the back-arc area approximately between 7.5 and 3.5 Ma. This period partly overlaps with the emplacement of the Larderello–Travale granites that started no later than 3.8 Ma, thus raising the possibility that compressive structures may have – at least in part – controlled magma emplacement, and/or also that the early emplacement of the Larderello–Travale granites occurred when the compressive stresses started to decay. In some cases, isotherms localize and elongate in the direction of subsurface anticlines in the basement, as occurs in the Travale area. Comparison with the results of analogue models indicates that the core of active and inactive fold anticlines in the basement may focus the upraising of magmatic fluids, with obvious implications for the geothermal exploration of the area.