Beginning of the Apennine subduction system in central western Mediterranean: constraints from Cenozoic orogenic magmatic activity of Sardinia (Italy)

Major and trace element analyses plus six new 40Ar/39Ar data obtained on feldspar separates for selected igneous rocks belonging to the Oligo-Miocene igneous activity of Sardinia are reported here. The rocks show ''subduction-related'' geochemical characteristics, ascribed to the metasomatic modification of a mantle wedge developed above a W/NW directed subduction system involving the recycling of Neo-Tethyan oceanic lithosphere beneath the southern European margin. The 40Ar/39Ar data shift back the beginning of the igneous activity in Sardinia to late Eocene (38.28 ± 0.26 Ma), whereas the end of the igneous activity is possibly shifted forward to late middle Miocene (12.24 ± 0.98 Ma). We therefore propose to rename the Oligo-Miocene igneous phase as the ''late Eocene-middle Miocene'' phase. Rare earth element inversion modeling on subduction-related volcanic rocks of Sardinia requires equilibrium with spinel-lherzolite facies, therefore implying depths of formation lower than 80 km. To reach these depths, a 45 dipping slab needs 11 to 4 Myr (with 1 to 3 cm/yr subduction velocity, respectively), reducing the beginning of Apennine subduction to the 49-42 Ma interval. The different models proposed in literature to explain the origin and the evolution of the central western Mediterranean basins are here reviewed and critically discussed.