Cenozoic extension in the Western Mediterranean is related to the dynamics of back-arc domains. However, extension propagated into the external Foreland Thrust Belts (FTB) of the region. Here we revisit the structure, metamorphism and radiometric ages of the Tunisian Tell FTB, where HP/LT blastomylonitic rocks (300-370ºC at 0.9-1.0 GPa), were exhumed by the sequential activity of extensional detachments. Normal faults thinning the Tunisian Tell FTB detached at two different crustal levels. The shallower one cuts down into the Atlas Mesozoic sequence, involving allochthonous Triassic evaporites at the base of the hanging-wall that form halokynetic structures intruding the Mejerda basin Late Miocene infilling. Meanwhile, the deeper-detachment level bounds metamorphic domes formed by marbles and metapsamnites. Illite crystallinity of Triassic rocks in the region shows epizonal to anchizonal values, at deep and intermediate structural depths of the Tell-Atlas FTB, respectively. New U-Pb 49.78 ± 1.28 Ma rutile ages together with existing K-Ar ages in marbles at the footwall of the deepest detachment, indicate a polymetamorphic evolution. The Tell Triassic rocks underwent Cretaceous extensional metamorphism, followed by crustal thickening and rutile growth in the Early Eocene. Further, Early Miocene thickening thrusted the metadolerites over lower-grade sediments, producing HP/LT metamorphism overprinting the base of the FTB. The exhumation of midcrustal roots of western Mediterranean FTBs after the tectonic shortening phase is a common feature of other FTB´s, like the Betics and Rif, which underwent a late-stage tearing at the edges of the subduction system together with delamination of their subcontinental lithospheric mantle.

We study the structure of the Llevant ranges in Mallorca with special emphasis in the Cenozoic extensional evolution of the island, which we integrate in a new geodynamic model for the Westernmost Mediterranean. Mallorca underwent two rifting phases in the Oligocene and Serravallian, before and after the development of its Foreland Thrust Belt (FTB). The first extensional phase produced Oligocene semigrabens (29-23 Ma) that were inverted during the Early-Middle Miocene (23-14 Ma) WNW-directed FTB development. The second rifting phase produced the extensional collapse of the Mallorca FTB during the Serravallian (14-11 Ma). This later rifting was polyphasic, with NE-SW and NW-SE directed transport, resulting in an overall sequential, radial extension. The Oligocene extension affected great part of the Western Mediterranean, opening the Liguro-Provenzal and proto-Algerian basins after the collapse of the Palaeogene AlKaPeCa orogen, and Mallorca, its former hinterland. Continued plate convergence nucleated a new subduction system in the Early Miocene that initiated along the Ibiza transform, producing the Mallorca WNW-directed FTB and the subduction of the South-East Iberian passive margin. A process that individualized the Betic-Rif slab and initiated its westwards retreat. Serravallian extension occurred at the northern edge of the subduction system coeval to the Algero-Balearic basin opening. Extension initiated towards the SW direction of slab tearing and later rotated to a NW-SE direction, probably related to flexural and isostatic rebound. These processes drove the Alboran domain archipelago southwestwards until the Late Miocene, contributing to the present isolation of the Mallorca FTB from its Betic hinterland.