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.