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The western Mediterranean late Oligocene–Miocene basins (Alboran, Valencia and Provençal basins) are a coherent system of interrelated troughs. In all basins normal faults and thermal subsidence migrated toward the east progressively moving to the Miocene‐to‐Pleistocene Algerian and Tyrrhenian basins. All those troughs appear elements of the back‐arc opening related to the eastward roll‐back of the W‐directed Apennines–Maghrebides subduction zone, similarly to western Pacific back‐arc settings. These late Oligocene–early Miocene basins nucleated both within the Betic cordillera (e.g. Alboran sea) and in its foreland (Valencia and Provençal troughs). The N40–70° direction of grabens is oblique to the coexisting N60–80°‐trending orogen and shows its structural independence from the orogenic roots. Thus, as the extension cross‐cuts the orogen and developed also well outside the thrust belt front, the westernmost basins of the Mediterranean had to develop independently from the Alps‐Betics orogen. Therefore, the Alboran extension, considered a classic example of a basin generated by the collapse of an orogen, cannot be ascribed to the detachment or annihilation of the lithospheric root. In contrast with the eastward migrating extensional basins, the Betic‐Balearic thrust front was migrating westward producing interference or inversion structures.

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A simple mechanism of arcuate fold belt and back‐arc basin formation is presented based on the opening of mega‐continental tension gashes along pre‐existing, deep, parallel and steep faults that separate lithospheric units with different properties. If plate convergence is parallel to these faults, the fault‐bounded units open at right angles to the convergence vector, adopting an arcuate shape with thrusting in front of the bowed‐out units and extensional basin opening between the separated units. This model is applied to the Cenozoic geodynamic evolution of the western Mediterranean. After the Iberian collision 35–30 Ma, several ellipsoidal basins (Valencia, Alboran, North Algerian and Liguro–Provençal) developed by 10 Ma along the eastern margin of the Iberian plate. The formation of these basins is attributed to an increase in NE–SW horizontal tectonic palaeostress during early–middle Miocene times resulting from the post‐subduction collision of the Tethyan oceanic lithosphere.

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