Somma-Vesuvio

Vesuvio lavas younger lhan 1631 AD Somma volcano  

Several ejected blocks are found in the Somma-Vesuvio pyroclastics. These include lavas, sedimentary carbonate rocks, skams, and mafic and ultramafic xenoliths (e.g. Joron et al. 1987). The latter have been suggested 

REE patterns show variable fractionation, with small negative Eu anomalies, which increase in trachytes and phonolites (Fig. 6.7a). HREE depletion is observed is some phonolites. Patterns of incompatible elements normalised to primordial mantle compositions for mafic rocks (Fig. 6.7b) are fractionated and contain positive spike of Pb and negative anomalies of HFSE. However, these are less sharp than in other Italian ul-trapotassic rocks, such as those of the Roman Province, and HFSE abundances are much higher than observed in MORBs (Sun and McDounough 1989). 

Oxygen isotope signatures of Vesuvio rocks show wide variations (S180 —1-7.0 to +10.0) and are negatively correlated with MgO (Ayuso et al. 1998). Helium isotope studies on clinopyroxene and olivine from historical lavas gave values of R/Ra 2.2 to 2.7, close to ratios found in the fumar-oles of Campanian volcanoes (Tedesco et al. 1990 Graham et al. 1993). 

Variation of many major and trace elements in the Somma-Vesuvio rocks suggest that fractional crystallisation was a main mechanism in magma evolution. Different trends shown by the various rock series for both major and trace elements have been interpreted either to reveal the presence of different types of parental magma and/or to indicate fractionation dominated by different relative amounts of clinopyroxene and feldspar, possibly as a consequence of variable pressure during fractionation (Joron et al. 1987 Trigila and De Benedetti 1993). 

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Campania and Pontine Islands (1 Mato Present) Somma-Vesuvio (0.03-1944 AD), Campi Flegrei (0.3-1538 AD), I-schia (0.15-1302 AD), Procida (0.05-0.01), Ventotene (0.8-0.1), younger Ponza (1). - Shoshonitic, potassic (trachybasalt to trachyte) and ultrapotassic (leucite tephrite to phonolite) rocks forming stratovolcanoes and multi-centre complexes. 

Volcano Somma-Vesuvio Age 30 ka to 1944 AD Volcanology and Petrology - Stratovolcano (Mount Somma) with multiple caldera and an intracaldera cone (Vesu-vio) formed of slightly to strongly silica undersaturated trachybasalt and leucite-tephrite to trachyte and phonolite. 

Fig. 6.3. Sketch map of Somma-Vesuvio volcano. Simplified after Civetta et al. (2004).

Fig. 6.4. TAS classification diagram for Somma-Vesuvio volcanics. Note different trends for groups of rocks with different ages.

Fig. 6.5. Variation diagrams of selected major and trace elements vs. SiC>2 for Somma-Vesuvio rocks. For symbols see Fig. 6.4.

Fig. 6.7. REE (A) and incompatible element (B) patterns (restricted to mafic compositions) for Somma-Vesuvio rocks. Patterns of average E-MORB and OIB (Sun and McDonough 1989) are also shown.

The volcanoes in the Campania Province, Pontine Islands and Vulture are composed of a wide variety of magma types. Silica undersaturated ultrapo-tassic volcanism is restricted to Somma-Vesuvio, whereas mildly undersaturated to oversaturated potassic rocks occur at Campi Flegrei, Ischia, Procida and Ventotene. In the latter two islands, low potassium compositions close to calc-alkaline basalts are found among lavas and lithic ejecta. Pliocene calc-alkaline rocks are found as rhyolites at Ponza and as basalts and basaltic andesites beneath the Campanian Plain. At Vulture, volcanism is highly enriched in both Na and K, a composition that is distinct from any other volcano in the Italian peninsula. 

An important feature of magmatism in Campania is that the Campi Flegrei mafic rocks are moderately potassic in composition but have very similar concentrations and ratios of several incompatible elements as the ultrapotassic rocks from Somma-Vesuvio these, however, contain higher concentrations of K and Rb (e.g. Peccerillo 2001). In other words, the positive correlation between potassium and incompatible elements observed in other Italian volcanic districts (e.g. Emici and Roccamonfma) is not so evident in Campania. 

Volcanic sector made up by volcanics of the Neapolitan potassic province (Somma-Vesuvio, Campi-Flegrei, Ischia, and Roccamonfina) (Peccerillo, 2005). 

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