Extension in the western Mediterranean commenced at 32-30 Ma and was primarily controlled by subduction rollback. The rapid rollback of the subduction hinge was accompanied by a relatively slow convergence between Africa and Europe. Therefore, convergence could not support the rate of subduction rollback, and extension occurred on the overriding plate.
During back-arc extension, marine basins progressively formed from north to south, floored either by thinned continental crust or new oceanic crust. The earliest basins began to form in Late Oligocene in the Gulf of Lion, the Ligurian Sea and Valencia Trough. In Early Miocene, back-arc extension propagated to Provençal, Algerian and Alboran basins, and in the Upper Miocene, extension in the Tyrrhenian Sea commenced.
Rifting led to breakup of continental terranes, which drifted and rotated as long as the subduction zone continued to rollback. Subduction rollback temporally or permanently ceased when continental crust arrived at the subduction zone, impeding subduction processes. The continental terranes have then been accreted to the continents and considerable crustal shortening occurred.