title: Chlorine as a geobarometer for alkaline magmas: Evidence from a systematic study of the eruptions of Mount Somma-Vesuvius.
abstract: Defining the magma storage conditions of a volcanic system is a major goal in modern volcanology due to its direct implications for the style of a possible eruption, and thus on the associated risk of any crisis and the necessary management and mitigation strategies. Below 200 MPa and at equivalent depths, the strongly non-ideal behaviour of the H-C-O-S-Cl-F system in the silicate melt causes unmixing of the fluid phase to form an H2O-rich vapour and a hydrosaline phase in equilibrium with the silicate melt, both responsible for buffering the chlorine (Cl) concentration. Following this equilibrium, the Cl concentration in melts may be used as a geobarometer for alkaline magmas. Systematic application of this method to the main explosive eruptions of Mount Somma-Vesuvius highlights two main magma ponding zones, at ~180-200 and ~100 MPa. At these pressures, the maximum pre-eruptive H2O contents for the different magma compositions can be estimated; the results obtained, largely in agreement with the current literature, therefore confirm the validity of the method. The Cl geobarometer may help scientists to define the variation of the magmatic reservoir location through time and thus provide strong constraints on pre-eruptive conditions, which are of utmost importance for volcanic crisis management.
authors.affiliation: Sorbonne Universités, UPMC Univ. Paris 06, CNRS, Institut des Sciences de la Terre de Paris (iSTeP), 4 place Jussieu 75005 Paris, France.
authors.forename: H
authors.initials: H
authors.lastname: Balcone-Boissard
authors.affiliation: Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ Paris Diderot, CNRS, F-75005 Paris, France.
authors.forename: G
authors.initials: G
authors.lastname: Boudon
authors.affiliation: Dip.to Scienze della Terra, Universita' degli Studi di Firenze, Via La Pira 4, 50121 Firenze, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Cioni
authors.affiliation: Department of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th St., NY, NY 10024-5192 USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Webster
authors.affiliation: Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ Paris Diderot, CNRS, F-75005 Paris, France.|Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse, Università degli Studi di Napoli Federico II, Largo S. Marcellino 10, 80138 Napoli, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Zdanowicz
authors.affiliation: Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse, Università degli Studi di Napoli Federico II, Largo S. Marcellino 10, 80138 Napoli, Italy.|Dipartimento di Fisica "E. R. Caianiello" Università degli Studi di Salerno, Via Giovanni Paolo II 132, 84084 Fisciano, Salerno, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Orsi
authors.affiliation: Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse, Università degli Studi di Napoli Federico II, Largo S. Marcellino 10, 80138 Napoli, Italy.|Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo La Malfa 153, 90146 Palermo, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Civetta