Geodynamic control on orogenic and anorogenic magmatic phases in Sardinia and Southern Spain: Inferences for the Cenozoic evolution of the western Mediterranean

The genetic relationships between orogenic (i.e. subduction related) and anorogenic (i.e. intra-plate) Cenozoic igneous phases have been investigated in two regions of the western Mediterranean area: Sardinia and Southern Spain. In Sardinia the ‘orogenic’ magmatism (38–12 Ma) is followed by the ‘anorogenic’ previous termvolcanism,next term mostly since about 6 Ma, whereas in Southern Spain the ‘anorogenic’ previous termvolcanismnext term follows the ‘orogenic’ phase (34–6 Ma) after a gap of 0–4 Ma in the Betic–Calatrava districts. The older orogenic magmatism (tholeiitic, calcalkaline and more potassic products) of both areas is related to the subduction of the Ionian oceanic lithosphere which developed beneath the Paleo-European-Iberian continental margin probably since Middle-Late Eocene. This subduction system migrated southeastwards with time up to its present position in the Eolian–Calabrian Arc and the Betic–Alboran regions along the Apennine–Maghrebide belt. Relics of subducted lithosphere are geophysically recorded as nearly-vertical bodies down to 500–600 km, flattening for several hundreds of kilometres under the Tyrrhenian–Sardinia and Betic–Calatrava areas, respectively. These relics of subducted slabs, which pond over large areas of the mantle transition zone, appear to play a significant role also in the genesis of the younger anorogenic magmas, whose major volcanic fields lie above the frontal part of the subducted slab where convective instabilities and upward mantle flow components are geophysically supported by laboratory and 3D numerical models. This dynamic response to subduction, involving localised mantle upwellings and remobilization of pre-existing mantle components, may have been a fundamental factor in the generation of anorogenic magmas. Due to slab roll-back and inter-arc extension in both Eolian–Tyrrhenian and Betic–Alboran regions, the magma sources of the previous orogenic phases can be completely replaced by “fresh” mantle diapirs from whic h anorogenic magmas will be generated. These magmas are invariably characterised by OIB isotopic signatures (HIMU and EMI) which are classically interpreted as long-term recycling of oceanic crust (plus variable sedimentary components) via ‘ancient’ pre-Paleozoic subduction events. We propose that the ‘recent’ Cenozoic subduction from which the orogenic series was generated, also had a dynamic influence on the younger anorogenic magmatism by remobilization of long-term isolated mantle components which resulted in the secular evolution of OIB-type magmas. In this view, the on-going subduction processes of the Mediterranean orogenic belts did not provide chemical “ingredients” to the mantle sources of the anorogenic magmas, but induced reactivation of older metasomatised mantle domains ultimately triggering magma genesis.