Sicily Province

Fig. 8.6. Sr-Nd (A) and Pb (B) isotope diagrams for the Sicily Province. Compositions of HIMU, DMM, MORB and European Asthenospheric Reservoir (EAR) are also shown. See text for explanation.

Fig. 8.22. Normative compositions of basaltic rocks (Si02 < 52 wt % MgO > 4 wt %) from the Sicily Province. Dashed arrow indicates increasing depth of magma genesis and degree of source metasomatism. Full arrow indicates degree of partial melting, increasing from about 3% to 20% for nephelinitic to tholeiitic magmas.

Overall, isotope and trace element data have led to the conclusion that the mantle sources beneath the Sicily Province are heterogeneous and result from the interaction between various mantle compositions or reservoirs. There is a lively debate on the origin and physical nature of these mantle compositions, not only in Sicily, but at a global scale (e.g. Hofmann 1997 Meibom and Anderson 2003). 

In contrast, Esperanca and Crisci (1995) and Trua et al. (1998) propose that magmatism in the Sicily Province is derived from young lithosphere that was enriched by addition of asthenosphere-derived melts. As recalled earlier, this is a relatively young process, which occurred during Permian-Triassic times. The young age of metasomatism is supported by Sr-Nd isotopic studies on the Iblei xenoliths, which give a pseudo-isochron of about 200 Ma (Tonarini et al. 1996). 

The Sicily Province consists of tholeiitic to Na-alkaline magmas. Most rocks are mafic in composition, ranging from basalt to hawaiite and nephelinite, except at Pantelleria where peralkaline acid volcanics (pantellerites) dominate. A few trachytic rocks occur at Etna, Ustica and as lithic ejecta at Linosa. 

Mafic rocks from the Sicily Province display variable abundances of incompatible elements, which increase from tholeiites to alkali basalts and nephelinites. However, all the rocks show low LILE/HFSE ratios, typical of intraplate basalts, in contrast with the high LILE/HFSE compositions of volcanism from the Aeolian arc and the Italian peninsula. They have a relatively restricted range of Sr-Nd isotopic compositions, but variable Pb isotopic ratios, which fall along a trend connecting HIMU and intermediate compositions between DMM and EMI mantle. 

Radiogenic isotopic variations for Sardinia Plio-Quaternary volcanics are accompanied by systematic modifications of trace element ratios (Lustrino et al. 2004a). For instance, Ba/Nb is higher in the northern than in the southern outcrops, whereas Ce/Pb is lower (Fig. 9.9). In general terms, the rocks from the southern occurrences have incompatible element ratios close to typical anorogenic magmas such as those of the Sicily Province,... 

The Sardinia Province contains a wide variety of rocks, ranging from subalkaline to Na alkaline and nephelinitic, and from mafic to felsic. Most rocks have relatively unradiogenic Sr and Pb isotopic signatures, resembling EMI mantle compositions. A few outcrops from southern Sardinia have isotopic and trace element signatures very close to the rocks of the Sicily Province. Plio-Quatemary volcanism in Sardinia overlies Oligo-cene-Miocene arc-type tholeiitic to calc-alkaline volcanism. 

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