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.