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 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.

Origin and evolution of Cenozoic magmatism of Sardinia (Italy). A combined isotopic (Sr–Nd–Pb–O–Hf–Os) and petrological view

“…Vogelsberg; Jung et al, 2005Jung et al, , 2011Pfander et al, 2012) Beccaluva et al, 1989;Gueguen et al, 1998;Lustrino et al, 2009;Carminati et al, 2012).…”

“…Trace element abundances and isotopic ratios of the less differentiated Late Eocene-Middle Miocene rocks led several authors to propose a derivation from a mantle wedge modified by slab-derived fluids (e.g., Morra et al, 1997;Mattioli et al, 2000;Downes et al, 2001;Franciosi et al, 2003;Lustrino et al, 2009;Conte et al, 2010;Guarino et al, 2011).…”

“…The geological setting and background of the island of Sardinia has been recently reviewed (e.g., Lustrino et al, 2009Lustrino et al, , 2011Carminati et al, 2010Carminati et al, , 2012 and for this reason only the most important aspects will be summarized here. Until the Oligocene, Sardinia and Corsica were part of the southern European paleo-margin.…”

“…The oldest igneous rocks (~38 Myr; Lustrino et al, 2009;Fig. 3) are represented by a small microdiorite body from Calabona area (N Sardinia).…”

“…2) In Sardinia two different igneous phases developed during the Cenozoic, the oldest (Late Eocene-Middle Miocene) is considered to be related to the originally NW-directed Apennine subduction system, whereas the youngest (Middle Miocene-Quaternary) volcanism seems geochemically unrelated to active or recent subduction processes (e.g., Lustrino et al, 2007aLustrino et al, , 2009Lustrino et al, , 2011; Fig. 1).…”