Shoshonitic rocks

REE patterns are fractionated silicic rocks contain negative Eu anomalies (Fig. 7.14a), which are much smaller than observed for the Lipari and Vulcano rhyolites. Mantle normalised incompatible element patterns of mafic rocks show high LILE/HFSE ratios and a positive anomaly of Pb a small positive Sr spike is observed in the calc-alkaline basaltic andesites (Fig. 7.14b). HKCA and shoshonitic rocks have higher incompatible element abundances than the associated CA products. 

The Aeolian arc is formed by calc-alkaline, high-K calc-alkaline and shoshonitic rocks, with some slightly undersaturated potassic alkaline lavas similar to the KS rocks from central Italy. Three sectors have been... 

Morra V, Secchi F A, Melluso L, Franciosi L (1997) High-Mg subduction-related Tertiary basalts in Sardinia, Italy. Lithos 40 69-91 Morris J, Ryan J, Leeman WP (1993) Be isotope and B-Be investigations of the historic eruptions of Mt. Vesuvius. J Volcanol Geotherm Res 58 345-358 Morrison GW (1980) Characteristics and tectonic setting of the shoshonite rock association. Lithos 13 97-108... 

Morrison G.W., 1980, Characteristics and tectonic setting of the shoshonite rock association. Lithos, 13, 97-108. 

Figure 1.199. Plot of K2O versus Si02 for volcanic rocks thought to be genetically related to Au mineralization. High sulfidation (HS) deposits appear to be associated with a narrow range of igneous rock composition, dominated by dacite and andesite. Low sulfidation (LS) deposits are largely associated with andesite and rhyolite, but major deposits such as Ladolam, Porgera and Cripple Creek are associated with shoshonitic and alkalic rocks (Hedenquist et al., 1996).

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. 

This is divided into a western, a central and an eastern sector. The western Aeolian arc (Alicudi, Filicudi, Salina) consists of calc-alkaline rocks with typical island arc signatures. Mafic and intermediate rocks dominate the volcanic sequence, with minor silicic volcanics. The central islands (Vul-cano and Lipari) are dominated by calc-alkaline to shoshonitic mafic to silicic rocks mafic rocks from this sector show isotopic compositions and incompatible trace element ratios similar to the western islands. The eastern arc (Panarea and Stromboli) consists of calc-alkaline to potassic alkaline rocks. Stromboli shows geochemical and isotopic signatures akin to the Neapolitan volcanoes. The Island of Panarea, located between Stromboli and Lipari, has intermediate characteristics between these two volcanoes (Calanchi et al. 2002a). 

Calc-alkaline, shoshonitic and potassic rocks Lamproiles... 

Fig. 2.7. Mantle normalised incompatible element patterns of representative Tuscany mafic rocks (A, B) and for mafic enclaves hosted by silicic rocks (C). The field of Aeolian arc calc-alkaline and shoshonitic mafic rocks is shown for comparison.

Rock type Monzo- granite Leuco- granite Monzo- granite Monzogranite Leucogranite Shoshonitic basalt... 

Rock type Andesite Latite Lamproite Lamproite Lamproite Lamproite Shoshonite... 

Ma (Metrich 1985 Metrich et al. 1988) and consists of basalt, trachybasalt, shoshonite, latite and phonolite (Fig. 6.18). The Pontine Islands are formed entirely of volcanic rocks, except for Zannone, where the sedimentary and metamorphic basement (phyllites, quartzites and Mesozoic to Miocene limestones, dolostones, marls and siltstones) crops out. 

Rock compositions range from mafic to silicic, and show a calc-alkaline (CA), high-potassium calc-alkaline (HKCA) to shoshonitic (SHO) affinity. A few potassic alkaline rocks with a composition close to the Roman potassic series (KS) occur at Vulcano and Stromboli (e.g. Keller 1982 Francalanci et al. 2004). Arc tholeiites have been dredged along some seamounts (Beccaluva et al. 1982). 

Stromboli 200 ka to present - Stratovolcano with summit caldera and flank collapses, and a satellite neck (Strombolicchio) formed of mafic to intermediate lavas and pyroclastic rocks with calc-alkaline, shoshonitic and potassic alkaline petrochemical affinities. 

The SiC>2 vs. K2O plot (Fig. 7.8) shows that the Lipari volcanics define a steep increase in K2O from mafic to intermediate rocks, straddling the limits between arc tholeiitic, calc-alkaline and shoshonitic series. Basaltic andesites and andesites have porphyritic textures with phenocrysts of zoned... 

Complex (20 and 15 ka), sited north of Primordial Vulcano, is the remnant of a stratovolcano with a central caldera (Fossa Caldera), mainly formed by latitic, trachytic and rhyolitic lava flows, domes, and pyroclastic rocks. Fossa Caldera products were erupted between 15 and 8 ka by pyroclastic and effusive eruptions of shoshonitic intermediate to silicic magmas. Cono della Fossa is a 391 m high active edifice that rises at the center of the Fossa Caldera it was formed in the last 6000 years by several silicic pyroclastic eruptions and a few lava effusions. Vulcanello is a shield made of mafic potassic lavas showing a KS affinity, with central trachytic pyroclastic cones. Vulcanello was formed as a new island probably about one thousand years ago (magnetostratigrafic age by Tanguy, personal communication) sand accumulation in the isthmus area finally connected Vulcanello with the main island. 

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