The viscosity of latitic melts from Lipari (Aeolian Islands, Italy): Inference on mixing–mingling processes in magmas

Abstract

The viscosity of latitic melts occurring as enclaves in the rhyolitic lava flow of Rocche Rosse (RR, Lipari, Aeolian Islands, Italy) has been measured in the high T range (1323–1473 K) for a dissolved water content varying from 1.23 to 4.39 wt.%. Measurements were performed by the falling sphere method in an internally heated gas pressure vessel. As expected, the viscosity of latite decreases with increasing water content and temperature. No pressure effect was detected between 200 and 500 MPa. Combining the new viscosity data for hydrous melts with data for dry latite of similar base composition [Giordano, D., Mangiacapra, A., Potuzak, M., Russell, J.K., Romano, C., Dingwell, D.B., Di Muro, A., 2006. An expanded non-Arrhenian model for silicate melt viscosity: a treatment for metaluminous, peraluminous and peralkaline liquids. Chemical Geology 229, 42–56.] we propose an empirical equation to estimate the viscosity of latitic melts as a function of temperature and water content over the range 10 1 to 10 12 Pa s. The obtained relationship reproduces the experimental data with a 1σ standard deviation of 0.22 log units. However, the empirical model is not constrained by data for hydrous melts at high viscosity and, therefore, it can only be used at low temperatures for water-poor melts. The viscosity data were used to model mixing–mingling processes between latitic and rhyolitic magmas at conditions relevant for the Rocche Rosse (RR, Lipari, Aeolian Islands) and La Fossa Cone 1888–1890 (LFC, Vulcano, Aeolian Islands) eruptions. The results demonstrate that the ratio between mafic and silicic end-members is the main parameter governing mixing–mingling interactions between magmas. This study suggests a faster ascent of magma underneath Vulcano compared to Lipari, which may be taken into account in hazard forecasting.