Lead isotopic composition of the potassic rocks from Roccamonfina (South Italy)

Abstract

Pb isotope data are presented for the potassic rocks from Roccamonfina and some other Campanian volcanoes. Pb isotope variations for Roccamonfina fall within the previously found range of values for the Italian potassic volcanism and form similar shallow regression lines in the Pb-Pb diagrams. Their interpretation as two-component mixing lines is well supported by other geochemical evidence. The relation of the mixing processes deduced for Roccamonfina and for the wider regional volcanism is discussed. The enriched and anomalous mantle under Italy is proposed to be a result of various degrees of metasomatism of a range of “Atlantic island” type mantle compositions by an LIL-element-enriched mantle “fluid”. The mantel “fluid” may either derive its isotope and trace element characteristics from an old LIL-element-enriched mantle source or from continental crust which has to some extend retained its geochemical identity in the upper mantle.