Petrology and Geochemistry of submarine volcanism in the Sicily Channel Rift

Abstract

Submarine magmatism in the Sicily Channel Rift began in the early Pliocene and lasted until almost 200 yr ago. We present here petrological and geochemical data on volcanic rocks dredged from Graham and Nameless banks and Pantelleria seamounts in the Pelagian sector of the Sicily Channel Rift. Petrological evidence suggests that the ascent of magmas to the surface was relatively rapid, probably through channels superimposed over the major tectonic discontinuities of the Rift. Major and trace element data indicate an ocean island basalt affinity for Graham and Nameless bank alkaline lavas and a depleted tholeiitic signature for one Pantelleria seamount, which had a shallower mantle source. Sr-Nd-Pb isotopic compositions suggest a heterogeneous mantle source involving both focus zone (FOZO) and high-m (HIMU) components. Lead isotopic compositions are slightly less radiogenic in the tholeiitic basalt and more radiogenic (closer to HIMU) in the alkaline lavas.We hypothesize that a decompressional meltingmechanism affected the mantle beneath the Sicily Channel at different levels. Our data fit in a regional scenario characterized by the presence of HIMU or FOZO components in alkaline and calc-alkaline volcanics all around Sicily. The explanation for the common isotopic composition could lie in a (fossil) plume head that variably contributed to magmatogenesis in response to variable lithospheric stretching.