Mount Etna as a window into the lubricants of plate tectonics

Flux or decompression melting of the mantle are the two main mechanisms proposed for the generation of magma beneath large stratovolcanoes. However, Mount Etna, one of the most active volcanoes on Earth, differs from active volcanoes in subduction zones or oceanic islands because of the eruption of large volumes of volatile-rich alkaline lavas over relative short time scales. This questions the mechanism of magma formation at depth as Mount Etna lavas requires specific melting conditions to account for their enrichment in alkali and other incompatible elements. Here, we link the origin of Mount Etna to the extraction of pre-existing melts in the Low Velocity Zone (LVZ). This zone characterizes the lithosphere-asthenosphere boundary (LAB) and is identified beneath oceanic plates by electric and seismic anomalies reflecting the presence of small melt volumes. We use geochemical data and modelling to show that volcanism in response to plate flexure around Sicily, when coupled with varying degrees of melt-rock interaction, accounts for the temporal and chemical evolution of magma and eruptive volume for both Mount Etna's lavas and the earlier volcanic activity on the Hyblean Plateau. Mount Etna may be a unique place on Earth where the composition of melts at the LAB, the essential rheological lubricants for global plate tectonics can be studied directly on the Earth’s surface.