Timescales of pre-eruptive magmatic processes at Vulcano (Aeolian Islands, Italy) during the last 1000 years

Abstract

An integrated petrological and geochemical study on plagioclase crystals erupted at Vulcano Island (Aeolian Islands, Southern Italy) over the past 1000 years allowed us to draw a detailed model of the internal structure of the volcanic system, in which modes of magma interaction and timescales of storage at crustal depth are shown. The integration of compositional, textural and temporal record preserved in plagioclase crystals provides evidence for an articulated plumbing system constituted by several reservoirs connected at the crust-mantle boundary. Here, a basaltic-shoshonitic magma resides and is thought to feed the shallow magma reservoir of both La Fossa and Vulcanello centers, finally triggering eruptions throughout injections from depth. Textural and micro-compositional data on plagioclase crystals suggest the presence of three main magma levels located between ca. 17 and 2 km of depth beneath La Fossa Cone, which were intermittently reactivated over the whole period of activity considered. Plagioclase textures and compositional zoning indicate that the shallow (<11 km bsl) portions of the La Fossa plumbing system were particularly active over the last 1000 years, as crystals record the ascent and continuous episodes of magma recharge and mixing that affect the shallower reservoirs. The first stage of activity at Vulcanello (i.e. Vulcanello I eruption) was fed by slightly differentiated melts that directly rose from the deep basaltic-shoshonitic reservoir, residing for a short period of time into the crust before the eruption. Indeed, diffusion modeling calculations on Sr zoning in plagioclase indicate shorter timescales of residence (<2 years) for crystals erupted at Vulcanello compared to those of the La Fossa Cone eruptions (ca. 2–10 years). If compared with the time span between eruptions occurred at La Fossa, our time estimations may suggest that magma feeding the activity at La Fossa resides most of the time in reservoirs located below the plagioclase nucleation depth (~11 km of depth), finally rising up only few years before the eruption onset. According to our model, magmatic eruptions at Vulcano Island are related to the ascent of deep basic (basaltic/shoshonitic) magmas that trigger a sort of “reaction chain” through subsequent episodes of recharge and mixing toward the upper magmatic reservoirs.