Tertiary compression and extension in the Sardinian basement

This study describes the Tertiary tectonics of Sardinia and its possible relationships to coeval tectonics in Corsica and to continental collision in the Northern Apennines. The most important Tertiary compressive features of Sardinia are the positive flower structures associated with sinistral transpressive faults that control the location of thrusting of the Paleozoic basement on the Mesozoic and Tertiary cover. The distribution of the deformation and the direction of shortening indicate that this transpression was associated with the collision between the Iberian plate continental margin and the Apulian continental margin. Emplacement of Corsican "Alpine" continental units and the transcurrent tectonics of NE Sardinia occurred after post-Middle Eocene clastic sedimentation and before the deposition of Burdigalian-Langhian neritic formations. Transpressive tectonics of NE Sardinia and of SW Corsica probably developed during the Oligocene-Aquitanian in the hinterland of the Northern Apennines during the ensialic evolution of this chain, During the Early-Middle Miocene, tectonic inversion from compression Io extension lead to a) the formation of the Sardinian rift; b) the exhumation of middle-crustal levels of the metamorphic core complexes of "Alpine" Corsica and Alpi Apuane and the development of the "serie ridotta" of Southern Tuscany; c) the transgression of Lower-Middle Miocene marine deposits over the Northern Apennines chain, over Sardinia and Corsica, in the Northern Tyrrhenian and in the Balearic basins. Extension continued during the Late Miocene and Phocene-Pleistocene with the development, in SW Sardinia, of the Campidano graben and, on the castern side of the island, with the opening of the Southern Tyrrhenian basin. This last extensional phase is contemporaneous with the NE-migration of the Northern Apennines thrust belt foredeep-foreland system. If the age of the initiation of post-collisional extension in "Alpine" Corsica and in Tuscany is indeed Early Miocene, it is likely that drifting of the Corsica-Sardinia block was contemporaneous with post-collisional extension of the Northern Apennines and not with the collisional tectonics of this chain as has been often accepted.