Recurrent evacuation of mantle mush by mafic recharge in ocean islands revealed by clinopyroxene from La Palma

Alberto Caracciolo , Teresa Ubide , Mónica Ágreda López, Raquel Herrera, Álvaro Márquez, Diego Gonzalez-Garcia, Maria Jose Huertas Coronel, Eumenio Ancochea, Nicolás Chicharro, Juan Jesus Coello-Bravo , Maurizio Petrelli 

Temporal variations in magma plumbing architecture and magmatic processes influence eruption priming and the interpretation of pre- and syn-eruptive signals. Yet, how these variations operate in low-flux ocean island volcanoes remains poorly constrained, leaving a key gap in understanding eruption precursors. Here we examine the temporal evolution of magmatic processes recorded in clinopyroxene at the Cumbre Vieja system in La Palma, Canary Islands, a low-flux ocean-island basaltic system characterized by nine eruptions in the last 1100 years. We decode clinopyroxene zoning from three historical eruptions during which lava composition transitioned from tephritic to basanitic: El Charco 1712, Teneguía 1971, and Tajogaite 2021. We combine major and trace element data from clinopyroxene crystals and carrier melts with textural observations, thermobarometry, quantitative trace element mapping, and cluster analysis of clinopyroxene zoning to reconstruct magmatic processes and storage conditions preceding these eruptions. Prior to each eruption, an evolved tephri-phonolitic to phonolitic crystal mush was stored in the upper mantle (∼18–25 km depth) and recycled and evacuated by injections of basanitic recharge melts. This mush was stored under relatively cool (1000 – 1025 °C) conditions and likely formed through 80–90% fractionation of basanitic magmas. At least one week before eruption, mafic recharge (1100 – 1150 °C) recycled this evolved mush and promoted magma ascent. Ascending magmas may have briefly stalled in the crust (at ∼5–10 km depth) prior to eruption, crystallising some of the clinopyroxene rims and microlites. Mafic recharge was critical in unlocking the mush, yet may not represent the immediate trigger for historical eruptions at La Palma. When compared across ocean island basalt systems worldwide, our findings suggest that evolved mushes may commonly develop in upper mantle plumbing systems, and their occurrence is likely controlled by the evolutionary stage of the volcanic island and the magma flux regime.