Experimental determination of H 2 O and CO 2 solubilities of mafic alkaline magmas from Canary Islands

We present new H 2 O and CO 2 solubility data in mafic to intermediate alkaline magmas from Fasnia and Garachico volcanoes, Tenerife. H 2 O-and CO 2-saturated experiments were conducted at ∼50-400 MPa, 1200°C, and f O 2 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 H 2 O and CO 2 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 H 2 O solubilities for both compositions, whereas the basanite can dissolve an average of ∼45% more CO 2 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 ⇐ 200 MPa (6-1.5 km).