Ponza island

Several volcanoes with calc-alkaline, tholeiitic (MORB and arc tholeiites) to Na-transitional and alkaline affinity coexist on the Tyrrhenian Sea floor. According to some authors (Savelli 1988 Locardi 1993), the calc-alkaline and shoshonitic seamounts developed along arcuate structures that become younger from west to south-east. The older volcanic cycle (4.5 Ma) of Ponza Island may represent the northern end of one of these arcs. 

Belkin, H. E., De Vivo, B., Lima, A., and Torok, K. (1996). Magmatic silicate/saline/sulphur rich/ CO2 immiscibility and zirconium and REE enrichment from alkaline magma chamber margins evidence from Ponza island, Pontine archipelago, Italy. Eur.J. Miner. 8, 1401—1420. 

Ylagan RF, Altaner SP, Pozzuoli A (2000) Reaction mechanisms of smectite illitization associated with hydrothermal alteration from Ponza Island, Italy. Clays Clay Minerals 48 610-631 Zhoukhlistov AP, Zvyagin BB, Lazarenko EK, Pavlishin VI (1977) Refinement of the crystal stracture of ferrous seladonite. Sov Phys Ciystallogr 22 284-288... 

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. 

Volcanic rocks in Campania and Pontine Islands range from mafic to felsic and mostly have silica undersaturated potassic to ultrapotassic compositions (Fig. 6.2). Mafic rocks with K2O contents close to calc-alkaline basalts have been found both as lavas and as lithic ejecta at Ventotene and Procida-Vivara. Pliocene (about 4.5 Ma) calc-alkaline rhyolites occur at Ponza, and 2 Ma old calc-alkaline basalts to andesites have been found by borehole drilling beneath the Campanian Plain north of Campi Flegrei. 

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. 

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