Petrological and geochemical characteristics of Plio-Pleistocene volcanics from Ponza island (Tyrrenian Sea, Italy)

Volcanic rocks on Ponza Island (Tyrrhenian Sea, central Italy) consist of Pliocene submarine ryolites and Pleistocene subaerial trachyte and comendite lavas. Chemical variations and the homogeneous Sr and Nd isotopic signatures within the analyzed Pliocene rocks are ascribed to chrystal fractionation. The absolute isotopic values, however, indicate the important role of a crustal component in the origin of these magmas. The very high-silica rocks were probably derived from a superimposed mechanism which may have been connected to the ascent of hydrothermal magmatic fluids. Compositional and 87 Sr/86Sr variations at constant 143Nd/144Nd values in the Pleistocenes rocks are like due to fractionation of the observed phenocryst assemblage, possibly coupled with minor crustal interaction. These processes, however, cannot account for the extreme enrichment of many incompatible trace elements in the comendites. Some evidence suggests the influence of a halogen-and/or CO2-rich volatile phase.