Magmatic feeding system and crustal magma accumulation beneath Vulcano Island (Italy): Evidence from CO 2 fluid inclusions in quartz xenoliths

Pure CO 2 fluid inclusions are observed in quartz xenoliths from four lava flows in the Island of Vulcano, corresponding to distinct activity stages during the last 120 kyr. Xenoliths, which consist of aggregates of quartz grains, are present in lavas of contrasting composition ranging from basaltic‐andesites to rhyolites. Two main generations of CO 2 inclusions are observed: early (type I) inclusions were trapped prior to the ascent of the host xenoliths, while type II inclusions were trapped during the ascent into the host magma. Fluid inclusions show a bimodal distribution of homogenisation temperatures, corresponding to two distinct density intervals: 0.89–0.52 g/cm 3 (type I) and 0.42–0.13 g/cm 3 (type II). Type I inclusions indicate pressures of 0.56–0.33 GPa (21–13 km), relating to the levels of xenolith entrapment in the host lavas. Type II fluid inclusions show considerably lower pressures ranging from 0.14 to 0.03 GPa (5.5–3 km). Present data suggest ponding of mantle‐derived magmas in at least two distinct reservoirs, located at lower crustal depths and at shallow levels, respectively. Combined fluid inclusion and petrological data suggest that the deep reservoirs were the sites of extensive fractional crystallization, mixing with source‐derived magmas, and various degrees of crustal assimilation. Evolutionary processes also occurred inside shallow magma chambers, in which deep magma mixed with residing melts and rested for short periods of time before being erupted to the surface.