Tectonic influence on magma storage and ascent during the older evolutionary stages (223-105 ka) of the Lipari island (Aeolian archipelago, southern Italy)

Pure CO2 fluid inclusions are observed in fifteen quartz-rich xenoliths collected in basaltic-andesitic to andesitic volcanic products relevant to the older evolutionary stages of Lipari Island (223-105 ka). In volcanics forming central composite volcanoes (M. Mazzacaruso, 223-127 ka; and M. S.Angelo, 105 ka), fluid inclusions are trapped during two distinct events: early Type I inclusions formed before host magma transport, and late (i.e. secondary) Type II inclusions trapped during magma ascent. Early Type I inclusions show homogenization temperatures corresponding to densities from 0.9 to 0.6 g/cm³, while Type II inclusions record a considerably lower density interval between 0.38 and 0.1 g/cm³. At the estimated trapping temperatures between 950 and 1090°C, obtained density values correspond to pressures of 0.58-0.25 GPa (22-16 km) for Type I, and 0.13-0.03 GPa (5.5-1 km) for Type II inclusions, respectively. In those magmas erupted from fissural eruptive vents aligned along the main regional NNW-SSE and E-W faults systems (Timpone Ospedale, Monterosa and M.Chirica; 223-127 ka) only early Type I inclusions are observed. Density values form to two distinct intervals between 0.8 and 0.6 g/cm3 (M. Chirica), and between 0.68-0.18 g/cm³ (0.32-0.05 GPa; 12-2 km; Timpone Ospedale and Monterosa). Fluid inclusion data together with tectonic features outline a complex magma storage and ascent evolution during the Lipari’s older evolutionary stages. Beneath the central volcanoes of M. Mazzacaruso, M. S.Angelo and the M. Chirica, two magma reservoirs, located at lower crustal depths (~22 km; close to the Moho) and at very shallow levels (5.5-1 km), are present. Mantle-derived magmas are accumulated into the deep magma chamber and may then reside in the shallower reservoir for a short period of time before being erupted to the surface. Such a magma feeding system is similar to those outlined for the Alicudi and Stromboli volcanoes, and for most of the Vulcano’s eruptive stages. Conversely, an intermediate magma reservoir at middle crustal levels (~12 km) is shown to play an important role in storage and differentiation processes of mafic magmas relevant to the fissural eruptive vents of Timpone Ospedale, Monterosa, and M. Chirica. Magmas more likely arise from the deepest magma storage level located close to the Moho, as outlined by M. Chirica eruptive vent. The proposed scenario is that the regional fault systems control the magma storage evolution, contributing to create a zone of preferential accumulation at mid- crustal levels. Fault systems may also influence magma ascent and determine the upward magma movement directly to the eruptive system without an effective ponding in the shallow reservoirs located at 5-1 km depth. At mid-crustal depths, magmas may reside for long time, and low rates of fractional crystallization occur. The occurrence of an intermediate storage level at similar depths beneath the rhyolitic Lentia domes at Vulcano, which are aligned along the main NNW-SSE tectonic trend, supports present model.