Li,Pb and Tl abundances in the K-alkaline rocks from the Middle Latina Valley volcanoes (southern Latium,Italy) and their petrological significance

Li, Pb and Tl contents of 15 primitive lava samples from the Middle Latina Valley volcanoes (southern Latium, Italy) are higher in the high-K than in the K-Series rocks, the enrichment factors roughly following the increase of the ionic size of the elements.The abundances in both series are higher than those of typical alkali basalts from oceanic environments, but similar to those of granitoid rocks. Such anomalous features may be explained as due to either crustal contamination of the parental magmas or derivation of these latter from a lithophile-enriched mantle region due to metasomatism by a lower crust-derived fluid. In both hypotheses, however, a larger involvement of crustal materials is suggested for the HKS rocks.Comparison of Li, Pb and Tl abundances in the primitive rocks of the Middle Latina Valley and Roccamonfina volcanoes shows that, unlike the KS rocks from the two districts show comparable levels and probably originated under similar conditions, the HKS rocks from the Middle Latina Valley are enriched in Li, Pb and Tl relative to their analogues from Roccamonfina. This suggests either a higher involvement of crustal materials in their genesis, or an evolution at shallower depth in the crust.