Petrogenesis and evolution of Mt. Vulture alkaline volcanism (Southern Italy)

摘要: The Late Pleistocene Mt. Vulture strato-volcano developed at the intersection of NE-SW and NW-SE lithospheric fault systems, on easternmost border Apennine compressional front overthrust onto Apulian foreland. initial phase volcanic activity is represented by pyroclastic deposits, including lava blocks, subordinate eccentric domes, mostly phonolitic in composition. later stages formed bulk (pyroclastic products lavas), tephritic composition, with minor intercalations basanite, mela-foidite melilitite lavas dikes. Variations rock mineral composition suggest that volumetrically predominant basanite-tephrite (foidite)-phonotephrite-phonolite series can be accounted for fractional crystallization processes starting from basanitic parental magmas, agreement remarkably constant 87Sr/86Sr isotopes (0.70586–0.70581). Mass-balance calculations indicate variably differentiated magmas may have been produced removal wehrlite, clinopyroxenite syenite cumulates, some which are occasionally found as cognate xenoliths volcanics. Fractionation probably multiple-zoned magma chambers, depths 3–5 km, corresponding to tectonic discontinuity between allochthonous formations underlying platform. Highly capping chambers their conduits thus appear fed activity, whereas dominantly were erupted stages. least evolved mafic namely basanites, mela-foidites melilitites, characterized diverse Na/K ratios critical SiO2-undersaturation, derivation independent melts generated distinct, heterogeneously enriched mantle sources variable partial melting degrees. Primitive mantle-normalized incompatible element patterns invariably share analogies both orogenic subduction-related (high Low Field Strength Elements/High Elements ratios, K, Rb Th contents marked Ti Nb negative anomalies) alkaline within-plate rift settings Light Rare Earth Elements, P, Zr, Na). These geochemical features generation deep sources, Na-alkali silicate/carbonatite anorogenic components, subsequently affected K-metasomatism, analogous modified Roman Magmatic Province along internal Chain.