Recurrent evacuation of mantle mush by mafic recharge in ocean island basalts, recorded by La Palma clinopyroxene

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 can modulate eruption priming, with direct consequences for interpreting pre- and syn-eruptive signals. However, how such processes unfold in low-flux volcanoes remains poorly constrained, leaving a gap in our understanding of eruption precursors. Here we examine the temporal evolution of magmatic processes at La Palma, Canary Islands, a low-flux ocean-island basaltic system, by interrogating the clinopyroxene zoning record from three historical eruptions during which lava composition transitioned from tephritic to basanitic: El Charco 1712, Teneguía 1971, and Tajogaite 2021. By combining major and trace element data from clinopyroxene crystals and carrier melts with textural observations, thermobarometry, quantitative trace element mapping, and cluster analysis, we reconstruct the magmatic processes and storage conditions preceding these eruptions. Both tephritic and basanitic magmas were stored in the upper mantle (18–25 km depth) together with an evolved tephritic to phonolitic crystal mush preserved in clinopyroxene antecryst cores. The phonolitic mush was stored at lower temperatures and likely originated by >80% fractionation of a basanitic melt. Repeated injections of basanite recharge melts gradually eroded and remobilized this mush, after which the recharge magma underwent 10-20% fractional crystallization, producing a tephritic melt. Despite its pivotal role in priming the system, mafic recharge did not act as the immediate trigger for the La Palma historical eruptions. Early-erupted tephrite-hosted clinopyroxenes lack clear recharge-related signatures in their inner rims, suggesting that eruption onset was more likely linked to internal evolution of the reservoir.