Melt inclusion constraints on the temporal evolution of magma and mantle during the 2021 Tajogaite eruption (La Palma)

Over geological timescales, processes such as subduction and convection have generated and distributed geochemical heterogeneities in the Earth’s mantle. Basaltic eruptions at oceanic islands sample the mantle and preserve their diverse geochemical signatures in crystal-hosted melt inclusions (MIs), revealing significant heterogeneity on short lengthscales. While mantle heterogeneity is well documented spatially, its temporal expression during the course of a single eruption, and its influence on magma evolution and volatile budgets, remain poorly constrained. 

The Canary Islands mantle is thought to comprise depleted and enriched lithologies overprinted by metasomatism involving carbonated and hydrous melts [1]. Here, we investigate how this heterogeneous mantle was sampled over the course of the 2021 Tajogaite eruption (La Palma), whose erupted products exhibited time-dependent geochemical variability [2]. We analysed olivine-hosted MIs using electron microprobe (major elements and S), ion microprobe (H₂O, CO₂, Cl, F), LA-ICP-MS (trace elements), and Raman spectroscopy (CO₂ density in bubbles). Since up to 85% of a MI’s volatile budget can be stored within its bubble [2,3], we also analysed experimentally homogenised MIs to reconstruct total volatile contents. We find temporal changes in MI compositions, including increasing MgO contents and decreasing Zr/Y ratios, consistent with progressive tapping of deeper and less fractionated magma batches during the eruption. Although H₂O contents decrease with time from 1.9 to 0.4 wt%, the highest CO₂ concentrations (up to 1.0 wt%) occur in homogenised MIs from Stage 2B of the eruption, suggesting enhanced contributions from CO₂-rich magmas.

We use time-resolved variations in REE ratios to trace changes in melting depth and the relative contributions of depleted and enriched melts; Rb–Ba–Nb–Ta systematics to constrain the role of minor hydrous phases; and Hf–Zr correlations to assess the imprint of carbonatitic metasomatism. By linking temporal variations in magma composition with in situ gas flux measurements and changes in eruptive style, we evaluate how the expression of mantle heterogeneity may have influenced gas emissions and eruption dynamics.

 

References: 

[1] Gómez-Ulla et al. (2018) Chemical Geology 10.1016/j.chemgeo.2018.07.015 

[2] Scarrow, J. H. et al. (2024) Volcanica 10.30909/vol.07.02.953980 

[3] Schiavi, F. et al. (2020) Geochemical Perspectives Letters 10.7185/geochemlet.2038 

[4] Buso, R. et al. (2025) Communications Earth & Environment 10.1038/s43247-025-02958-y