Deciphering post-caldera volcanism: insight into the Vulcanello (Island of Vulcano, Southern Italy) eruptive activity based on geological and petrological constraints

Abstract

Integrated field-based volcanology and petrologic studies can provide relevant clues about the way in which structural features, magma replenishment of a shallow subcaldera reservoir, and magma evolution exert control on eruption behavior during post-caldera volcanism. Post-caldera activity of the past 1000 years at the La Fossa caldera (Island of Vulcano, Italy) occurred at two vents: the dominantly explosive La Fossa vent located at the center of the caldera and the lava-dominated Vulcanello vent located close to the northern ring fault of the caldera. Revised chrono-stratigraphic data indicate that the activity occurred in two clusters of eruptions: in the eleventh to twelfth centuries and during the seventeenth century. The activity was, in part, contemporaneous with La Fossa vent and led to the formation of three, partially overlapped Strombolian cones. Each cone-building episode was accompanied by the outpouring of lava in subaerial and submarine environments. The erupted volumes of the pyroclastic cones vary between 2 × 10−3 and 3 × 10−6 km3, while the volumes of the three lavas span between 0.3 km3 (a submarine lava field) and 3 × 10−3 km3. Petrology data indicate that the activity of Vulcanello was fed by three different magma batches: Vulcanello 1 was fed by a slightly zoned reservoir of shoshonitic composition, Vulcanello 2 was fed by a slightly more evolved magma whereas Vulcanello 3 was fed by latitic magma. The compositions of melt inclusions (major elements and volatile content) trapped in olivine separated from pyroclastic materials record the entire differentiation history and suggest that all Vulcanello magmas underwent volatile loss during pre-eruption equilibration at ≤1 km depth. Integration of all available information also suggests that in the last 1000 years, the northern caldera fault acted as a preferential duct for the rise of degassed magma from the sub-caldera magma reservoir whereas volatile release namely took place separately at La Fossa cone where activity was almost entirely explosive in nature.