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A deep, narrow, and distorted Benioff zone, plunging from the Ionian Sea towards the southern Tyrrhenian basin, is the remnant of a long and eastward migrating subduction of eastern Mediterranean lithosphere. From Oligocene to Recent, subduction generated the Western Mediterranean and the Tyrrhenian back-arc basins, as well as an accretionary wedge constituting the Southern Apenninic Arc. In the Tyrrhenian Sea, stretching started in late Miocene and eventually produced two small oceanic areas: the Vavilov Plain during Pliocene (in the central sector) and the Marsili Plain during Quaternary (in the southeastern sector). They are separated by a thicker crustal sector, called the Issel Bridge. Back-arc extension was rapid and discontinuous, and affected a land locked area where continental elements of various sizes occurred. Discontinuities in extension were mirrored by changes in nature of the lithosphere scraped off to form the Southern Apenninic Arc. Part of the tectonic units of the southern Apennines, accreted into the wedge from late Miocene to Pliocene, had originally been laid down on thinned continental lithosphere, which should constitute the deep portion of the present slab. After Pliocene, only Ionian oceanic lithosphere was subducted, because the large buoyancy of the wide and not thinned continental lithosphere of Apulia and Africa (Sicily) preserved these elements from roll back of subduction. After Pliocene, the passively retreating oceanic slab had to adjust and distort according to the geometry of these continental elements. The late onset of arc volcanism in respect to the duration of extension in the Tyrrhenian-Ionian system may find an explanation considering an initial stage of subduction of thinned continental lithosphere. The strong Pleistocene vertical movements that occurred in the whole southeastern system (subsidence in the back-arc basin and uplift in the orogenic arc) may instead be related to the distortion of the oceanic slab.

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