Reconstruction of the intensive variables and magmatic architecture of Vulcano Island (Aeolian Arc, Italy)

In this study, we present new mineralogical and petrological data from fifteen eruptive products erupted at Vulcano Island (Aeolian Arc, Italy) over a period of time from 54 to 8 ka and representative of the Eruptive Epochs from 5 to 8 of this volcanic system. These rocks show shoshonitic (SHO) to high-K calc-alkaline (HKCA) affinity, with compositions changing from primitive basalts-shoshonites (Mg#35-60) to intermediate latites (Mg#32-54) to evolved trachytes-rhyolites (Mg#23-40). The intensive variables driving the crystallization path of magmas were reconstructed through mineral-melt equilibrium and thermodynamic models, as well as barometers, thermometers, hygrometers and oxygen barometers. The stability of olivine (Fo59-91), as first phase on the liquidus, is more favored at low-P (100-300 MPa) and high-H2O (4 wt.%) contents dissolved in the melt. Afterwards, the melt is co-saturated with clinopyroxene (Mg#92, diopside), whose composition progressively evolves (Mg#71, augite) as the temperature decreases to 1100 °C. The crystallization pressure recorded by clinopyroxene decreases from basalts (550-750 MPa) to shoshonites-latites-trachytes (100-450 MPa) to rhyolites (~50 MPa). The melt-H2O content (0.5-4.2 wt.%) is sensitive to either pressure or melt composition, thereby controlling the plagioclase stability and chemistry (An13-77) within a thermal path of ~860-1100 °C. Titanomagnetite (Usp11-39) equilibrates with progressively more oxidized melts as the magma composition changes from basalt (ΔQFM+1.5) to rhyolite (ΔQFM+3). Mass balance calculations and trace element modeling indicate that basaltic to trachytic magmas are prevalently controlled by fractional crystallization processes, in concert with variable degrees of assimilation of crustal rocks. Conversely, rhyolitic and highly differentiated trachytic magmas are generated by extraction of interstitial melts from shallow mush zones dominated by feldspar and titanomagnetite saturation. We conclude that the architecture of the plumbing system at Vulcano Island is characterized by multiple reservoirs in which compositionally distinct magmas pond and undergo polybaric-polythermal differentiation, before erupting to the surface.Here we document how the different growth features and intracrystalline distributions of both major and trace cations in clinopyroxene phenocrysts are important recorders of the intricate magma dynamics at Vulcano Island (Aeolian Arc, Italy). The compositions of clinopyroxene phenocrysts from products erupted over the last 54 ka cluster at different degrees of evolution, paralleling the polybaric-polythermal differentiation of mantle-derived mafic magmas into more evolved silicic melts. The hotter lower crust is the most favorable location for the storage of mafic magmas and the early crystallization of diopsidic (Mg#91) clinopyroxene (Pmax 750 MPa and Tmax 1,220 °C). Diopsidic phenocrysts are depleted in both rare earth elements (REE) and high field strength elements (HFSE) but are enriched in transition elements (TE). The transfer and accumulation of primitive magmas in the colder upper crustal regions lead to the formation of an interconnected series of more differentiated magmatic reservoirs (P 100-450 MPa and T 1,100-1,180 °C) hosting discrete populations of clinopyroxene (Mg#84-85) with a broad spectrum of zonations and dissolution features. Recharge bands in clinopyroxene are markers of multiple inputs of primitive REE-HFSE-poor, TE-rich magmas from depth. Augitic phenocrysts (Mg#82) with strong negative Eu anomaly and REE + HFSE enrichments crystallizes from highly differentiated trachytic and rhyolitic melts stored at very shallow crustal conditions (P ≤ 50 MPa and T ≤ 1,100 °C). These silicic reservoirs represent residual melts trapped-extracted from crystal-dominated mush regions in the uppermost part of the plumbing system. The residence time of clinopyroxene increases from ∼0.1 to ∼44 years from basalt to rhyolite, together with an increasing number of recharge bands. The mineral assemblage in more silicic and viscous mush melts is sufficiently resilient to record numerous mafic injections and high degrees of magma mixing, hybridization, and crystallization before eruption. Overall, the compositional zoning pattern of clinopyroxene presents a picture of plumbing system that extends through the crust and is characterized by distributions of melts and crystals which are progressively more evolved and heterogeneous in both space and time