Sardinia

Abstract

Sardinia is the site of three stages of volcanic activity that show variable ages, geochemical-petrological characteristics and geodynamic significance. An early stage of Oligo-Miocene activity erupted dominant calcalkaline basalt to rhyolite lavas and pyroclastics. Similar magmatism also took place in the Corsica-Ligurian basin and in Provence, southeastern France. Compositions show typical arc-type (orogenic) characteristics and are related to a mantle wedge contaminated by fluids released by the west-dipping Neotethys ocean lithosphere. The following activity is Miocene-Quaternary in age and shows OIB-type anorogenic geochemical signatures. It took place during two stages. An early Upper Miocene to Lower Pliocene (about 12 and 4.5 Ma) activity emplaced low-volume Na-alkaline mafic to intermediate magma bodies. This was followed by a more voluminous Plio-Pleistocene stage that emplaced large amounts of tholeiitic to Na-alkaline volcanics in central-northern Sardinia. These two stages of volcanism share anorogenic trace element characteristics (i.e. low LILE/HFSE ratios) but show significant geochemical and isotopic diversities. The Mio-Pliocene anorogenic rocks are compositionally similar to other anorogenic centres in the Mediterranean region, and probably originated in the lower lithospheric or upper asthenospheric mantle passively ascending during the Mio-Pliocene extensional phases of the Sardinia block. The younger anorogenic stage shows unradiogenic Pb-isotope compositions similar to EM1-type mantle component, a unique case in Europe. The origin of such a component is controversial and could be related either to a deep plume or to an anomalous lithospheric mantle, which had undergone a Paleozoic or Pre-Cambrian contamination by acidic melts originated from delaminated lower continental crust.