Magmatic Storage and Volatile Fluxes of the 2021 La Palma Eruption

Abstract

The 2021 La Palma eruption (Tajogaite) was unprecedented in magnitude, duration, and degree of monitoring compared to historical volcanism on La Palma. Here, we provide data on melt inclusions in samples from the beginning and end of the eruption to compare the utility of both melt and fluid inclusions as recorders of magma storage. We also investigated compositional heterogeneities within the magmatic plumbing system. We found two populations of olivine crystals: a low Mg# (78–82) population present at the beginning and end of eruption, recording the maximum volatile contents (2.5 wt % H ₂O, 1,800 ppm F, 700 ppm Cl, 3,800 ppm S) and a higher Mg# (83–86) population sampled toward the end of the eruption, with lower volatile contents. Despite their host composition, melt inclusions share the same maximum range of CO ₂ concentrations (1.2–1.4 wt %), indicating olivine growth and inclusion capture at similar depths. Overall, both melt and fluid inclusions record similar pressures (450–850 MPa, ∼15–30 km), and when hosted in the same olivine crystal pressures are indistinguishable within error. At these mantle pressures, CO ₂ is expected to be an exsolved phase explaining the similar range of CO ₂ between the two samples, but other volatile species (F, Cl, S) behave incompatibly, and thus, the increase between the two olivine populations can be explained by fractional crystallization prior to eruption. Finally, based on our new data, we provide estimates on the total volatile emission of the eruption.

Plain Language Summary

Melt inclusions, droplets of magma trapped during olivine crystal growth, record both evolved and primitive melts at the same depths exhumed during the 2021 Tajogaite eruption.

Key Points

• Melt and fluid inclusion record sub‐Moho storage depths

• Melt inclusions from the same crystal population can lose up to 1.5 wt% H ₂O within a single eruption through diffusive re‐equilibration during magma replenishment

• Heterogeneous abundances of volatiles in melt inclusion populations reflect pre‐eruptive fractional crystallization