Magmatic Evolution and plumbing system of ring-fault volcanism: the Vulcanello Peninsula (Aeolian Islands, Italy)

Abstract

The Vulcanello peninsula is situated north of Vulcano, the southernmost island of the Aeolian Arc. It was built at the rim of La Fossa Caldera between 1000 and 1650 A.D. Erupted products are mafic to intermediate in composition, while the coeval products erupted inside the caldera are mainly rhyolitic. Therefore, Vulcanello’s activity represents an anomalous mafic post-caldera volcanism in a convergent setting. A petrographic and geochemical study was carried out on lavas and pyroclastic rocks representing the entire eruptive history of the volcanic centre. New data (major and trace elements and Sr isotope ratios on whole rocks, and major element compositions on mineral phases) and geochemical models were used to investigate shallow level differentiation processes ( i.e. , fractional crystallisation, fractional crystallisation plus crustal assimilation, degassing, magma mixing/recharge). The study suggests that the entire Vulcanello activity can be considered as the uninterrupted expulsion of a single deep magma batch of shoshonitic composition emitted from a NE–SW ring fault of La Fossa Caldera. The magma is genetically related to the shoshonitic basalts found as melt inclusions in the olivine crystals erupted in the products of the 1888–1890 “ La Fossa” activity. This points to a possible single deep plumbing system for both La Fossa Cone and Vulcanello centres, strongly controlled by NW–SE to N– S regional structures. The shoshonitic magma, undergoing fractional crystallisation, partly rose directly to the surface where two strombolian cones were constructed, while residual magma remained at depth, and, partially degassed and crystallised, it subsequently erupted both effusively to form a lava platform and explosively to form a third pyroclastic cone. The remaining magma evolved to latite by AFC process and was erupted both as a lava flow (Punta del Roveto) and in the form of pyroclastic products ( i.e. , the upper part of the third cone), controlled by shallow ring faults of La Fossa Caldera. Therefore the Vulcanello plumbing system is controlled by tectonic structures at depth and by shallower volcano-tectonic (caldera) fractures.