Thermo-mechanical evolution and rheology of the northern sector of the Tyrrhenian–Apennines system

The connection between the thermal field and the mechanical properties in the northern sector of the Tyrrhenian–Apennines system is analysed. The thermal setting is the result of three main extensional events, which have taken place within relatively small space and time intervals. The oldest tectono-thermal event took place in eastern Corsica 14 Myr ago and the second between Capraia and Elba islands 7 Myr ago. The third and youngest rift episode, with an average age of 3 Myr, affected a wider area extending east of Elba Island and including most of the peri-Tyrrhenian zone. By assuming lithosphere extension, the expected Moho temperature increases eastward from 550 to 750 °C. Uniform stretching cannot account for the high heat flux in the zone affected by the youngest tectono-thermal event. For this zone, we propose a thermo-mechanical model, which incorporates the removal of 15 km of mantle lithosphere, as a result of eastward asthenosphere flow induced by the Apennines subduction. This yields a predicted heat flux in agreement with that observed. Lithosphere mechanical strength analysis indicates that the thickness of the uppermost crustal–brittle layer decreases eastward from 15 to 10 km, while the temperature discriminating the rheological behaviour is rather uniform, being on average, 320 °C.