Beginning of the Apennine subduction system in central western Mediterranean: Constraints from Cenozoic "orogenic" magmatic activity of Sardinia, Italy

Abstract

Major and trace element analyses plus six new 40 Ar/ 39 Ar 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 40 Ar/ 39 Ar 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 spinellherzolite 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. Copyright 2009 by the American Geophysical Union.