The explosive-effusive transition within the Miocene Fataga suite, Gran Canaria

Abstract

Many volcanoes show transitions between explosive and effusive eruptive styles both through the history of the volcano as a whole and occasionally within the course of a single eruption. These differing eruptive styles have vastly different implications for hazard assessments in surrounding regions and so understanding such changes is important. Here, we investigate the intercalated lavas and ignimbrites of the Miocene Fataga Group on the island of Gran Canaria, Spain. Ignimbrites reflect the products of explosive events from the Tejeda caldera, while lavas found within the pyroclastic succession were erupted from extra-caldera sources some 5–10 km from the caldera margin. The ignimbrites exhibit textural complexity containing both crystal-poor juvenile pyroclasts and late-erupted crystal-rich juvenile clasts interpreted to reflect interaction between cumulates and recharge magmas. The lavas meanwhile are almost phenocryst-free, with the exception of few large (cm-scale), unzoned sanidine crystals. Despite their textural differences, the lavas are geochemically similar (in terms of bulk rock and feldspar compositions) to the crystal-poor juveniles in the ignimbrites. Oxygen and lead isotopic compositions of the lavas and surrounding ignimbrites reveal that the magmas shared a deeper source and that petrographic variability is imprinted upon the magmas at shallow levels. We interpret the lavas as originating from peripheral magmatic pockets, on the edges of the main caldera-feeding reservoir. These peripheral magma chambers felt the effects of recharge only as slight thermal fluctuations that fostered the production of the large sanidine crystals. Our findings highlight the potential for storage of magmas aside from the main magmatic system that may represent an underappreciated hazard at volcanoes worldwide.