Water solubility and speciation in shoshonitic and latitic melt composition from Campi Flegrei Caldera (Italy)

Abstract

We report new data on water solubility in two melt compositions representative of volcanic units of the Campi Flegrei Caldera (Italy). The first composition is a primitive shoshonite and the second one is a more evolved latitic composition that have been chosen because of their less evolved nature compared to the other erupted products of Campi Flegrei. Water solubility was investigated at pressures from 25 to 200 MPa and 1200 °C following synthesis in an Internal Heated Pressure Vessel (IHPV). The glasses obtained from water-saturated experiments were analysed using both Fourier Transform Infra Red spectroscopy (FTIR) and Karl Fischer Titration (KFT). KFT was used as an independent method to obtain water concentration for the calibration of molar absorptivities of infrared bands at ∼3550 cm−1 (total water), ∼4500 cm−1 (hydroxyl groups) and ∼5200 cm−1 (molecular water). Water solubility in the shoshonitic melts is similar to that of a basalt while a slightly higher water solubility is observed for the latitic composition. As regards the speciation, we have investigated the water speciation for the shoshonitic composition only and we have made a comparison between the data resulting using different molar absorptivities obtained for basaltic compositions similar to our shoshonite.