5 de novembre de 2021

María Jiménez-Mejías; Joan Andújar; Bruno Scaillet; Ramón Casillas. Experimental determination of H2O and CO2 solubilities of mafic alkaline magmas from Canary Islands. Comptes Rendus. Géoscience, Online first (2021), pp. 1-26. doi : 10.5802/crgeos.84.

Abstract

We present new H2O and CO2 solubility data in mafic to intermediate alkaline magmas from Fasnia and Garachico volcanoes, Tenerife. H2O- and CO2-saturated experiments were conducted at ∼50–400 MPa, 1200 °C, and fO2 from 2 log units below the NiNiO solid buffer to 3.2 log units above it. Although existing solubility models for alkali-rich mafic magmas broadly describe H2O and CO2 behaviour, associated errors are worthy of consideration since they usually exceed 15–20%. For this reason, we have determined the specific solubility laws of basanitic and phonotephritic melts from the Canary Islands. Results show similar H2O solubilities for both compositions, whereas the basanite can dissolve an average of ∼45% more CO2 than the phonotephrite. By combining these data, we have established a simple empirical model that allows us to calculate melt inclusion entrapment pressures accurately and, therefore, better understand the inner workings of volcanic oceanic islands. Application to El Hierro 2011–2012 and young (<20 ka) basanites from this location shows that previous barometric estimates were, on average, overestimated by 15–28%. Our results suggest that magmas rising from depth experienced a first but short episode of equilibration at 8–10 km, whereas the bulk of the crystallization occurred during the subsequent dyke injection, ascent, and degassing at P⇐200MPa (6–1.5 km).