How did crustal thinning help create the Tyrrhenian Sea?

The Tyrrhenian Sea was formed through the southward drift of the Calabrian peninsula, which previously lay against Sardinia. This movement was part of a broader tectonic process where fragments of crust separated from southern Europe and drifted across the western end of the ancient Tethys Ocean, opening the new western Mediterranean basin behind them.1

While the Apennines were being built by the folding and faulting of sedimentary rock, the region experienced complex crustal dynamics. The opening of the Tyrrhenian basin is specifically linked to the southward migration of the Calabrian arc, a process involving crustal extension and thinning as these crustal fragments shifted. This tectonic activity is distinct from the crustal shortening that characterizes the mountain-building processes of the Apennines themselves.1