The Tyrrhenian Sea is classified as a back arc basin(Lavecchia & Stoppa 1990; Zamboni 2003) in the Western Mediterranean surrounded, mainly by Italy. Back arc basins occur in front of a subduction zone that is undergoing rollback and causing the overriding plate to also move in the same direction, which causes the extension (back arc) of the overriding lithosphere which causes the melting of the mantle due to decompression.
The subduction zone in this case has moved from the northern part of the Tyrrhenian area southeast ward to where it is now, just south of Calabria (Sartori et al. 2004; Calanchi et al. 2002), with this movement, the Tyrrhenian Sea opened, therefore from a geochemical perspective there must be rocks that have a geochemical signature of a subduction process (Volcanic arc) and rocks that show a geochemical signature of back arc rifting to confirm that it is indeed a back arc (Girolamo 1978).
The volcanic arc that has form in front of this subduction zone is the Aeolian arc to the NNW of Sicily (Calanchi et al. 2002). This arc of islands is formed by melts that formed as a product of subduction (partial melting) and is characterised by rocks that are normally enriched in potassium (K) and is of a calc-alkaline to shoshonite nature (Gertisser & Keller 2000; Lavecchia & Stoppa 1990; Girolamo 1978) with very low TiO (typically below 1.1-wt%) values and higher K2O values of about 2-wt% (Girolamo 1978). These islands have an island arc composition and are also quite strongly enriched in incompatible elements such as the large ion lithophile elements (LILE)(Trua et al. 2010; Lavecchia & Stoppa 1990).The Marsili basin (site 650 9n ODP leg 107), northwest of the Aeolian Arc, in the Southern Tyrrhenian sea shows a close affinity to converging plate margins (a calc alkaline trend) towards the upper part of the Marsili seamount (centre of the basin) (Beccaluva et al. 1990), the Th-Ti, Th-Nb and Ce-Nb ratios are more typical of converging margins, lower than mid ocean ridge basalts (MORB), although these rocks represent a magma with closer affinity to a volcanic arc such as the close by Aeolian arc, the Marsili basin is an extensional basin and the type of magma (more enriched and calc alkaline) could come from the steeply dipping close by subducting plate which could undergo partial melting introducing enriched melts into the system and dissolved alkalis can also be transported from the subducting plate and make its way up towards the seamount, Girolamo (1978) dredged rocks at the base of the seamount which from its TiO and low K2O-wt% values depict a magma more related to rifting, following a tholeiitic trend, thus this seamount has undergone an evolution from a tholeiitic nature when it was the spreading centre for the back arc to the calc alkaline nature it now has (Girolamo 1978; Beccaluva et al. 1990; Trua et al. 2010).
With the exception of the Marsili seamount that started as a more tholeiitic type and changed into a calc alkaline...