Crystal cargo perspectives on magma assembly and dynamics during the 2021 Tajogaite eruption, La Palma, Canary Islands

The 2021 Tajogaite eruption was the longest and most voluminous in recorded history on La Palma, Canary Islands. Extensive geophysical and geochemical data were collected before and during the eruption; however petrological monitoring saw little usage, largely restricted to rapid stereo microscope observations or off-island analyses. Here, we analyse lava and tephra sampled at near-daily frequency to investigate magmatic processes driving petrological, geochemical, and geophysical variations. Published whole-rock major and trace element data are combined with new QEMSCAN textural and mineral abundance data, major element analyses of macrocryst phases, and clinopyroxene trace element data, supported by mineral growth pressure–temperature modelling. Olivine Fe-Mg diffusion timescales from early tephra are compared with timescales of climactic unrest. Results indicate that more-evolved, mineralogically diverse magmas were tapped during the first week. Magma mixing only becomes apparent when more primitive magmas erupted after the first ~10 days, exemplified by reverse-zoned olivines. Clinopyroxene barometry suggests most material is fed from the upper mantle throughout. Timescales overlap and extend climactic unrest records, suggesting that destabilisation began before geophysical detection. From Stage 2 (~5–10 days) to eruption cessation (~85 days), crystal cargo chemistry is surprisingly uniform, with previously observed whole-rock and tephra glass changes not obviously reflected in the mineral record. We highlight the importance of combining both whole-rock and mineral scale observations to understand how eruptions progress, and ultimately end.