The 2021 Cumbre Vieja eruption (La Palma, Canary Islands): new perspectives on the geochemistry of lavas and noble gases isotopes trapped in fluid inclusions

We collected samples from the lava flows from the Cumbre Vieja 2021 eruption, the 1677 San Antonio eruption and picrites from the 3 Ma old Taburiente calderaand in La Palma (Canary Islands) with the aim to investigate the geochemistry of the lavas and their He and CO2 isotopic composition in fluid inclusions. The above information is crucial to better understand the evolution in time of the volcanic system and the nature of the local mantle source.

Our results suggest that during the Cumbre Vieja eruption there was a systematic increase in the volatile concentrations (particularly He and CO₂) between late September and early October. The above is accompanied by an increase of the whole rock Mg#, CaO/Al₂O₃ and the Nb/La ratios from 50.5 to 58.7, from 0.78 to 0.87, and from 0.88 to 1.01, respectively (we also observed that these variations coincide with the occurrence of deeper earthquakes; 30-40 km; D’Auria et al., 2022), which likely indicate the intrusion of a more primitive less-degassed magma rising from the asthenosphere at the end of September. Regarding the mineral chemistry, the composition of olivine and pyroxene do not show any noticeable heterogeneity in all analyzed samples. The ³He/⁴He ratios are homogeneous over time and exhibit MORB-like signatures between 7 and 7.5 Ra. In comparison the whole rock composition and the ³He/⁴He ratios of the San Antonio lavas are very similar to the lavas erupted in late October-early November 2021, whereas the picritic lavas from the Taburiente caldera show higher ³He/⁴He ratios equal to 9.4±0.1 Ra that are comparable with the signatures measured in the Dos Aguas cold spring (Pérez et al., 1994; Padrón et al., 2022) indicating plume origin.

In conclusion, the He isotopic differences between lavas form northern and southern La Palma could be advocated to the small-scale heterogeneities in the mantle, and/or a plumbing system responsible for the lower ³He/⁴He of the 2021 Cubre Vieja magmas.  Moreover, considering the more radiogenic helium ratios reported in mantle xenoliths from La Palma (6.5 - 7.2Ra; Sandoval Velasquez et al., 2022) we propose that the isotopic signatures observed at Cumbre Vieja and San Antonio are likely the result of a mixing between a plume component (highlighted by the ³He/⁴He in the picrites and the Dos Aguas Spring of the Taburiente caldera) and a more radiogenic reservoir located in the shallower lithospheric mantle.