Petrology of the explosive deposits from the April 2021 eruption of La Soufrière volcano, St Vincent: A time-series analysis of microlites

H. M. Frey, M. R. Manon, J. Barclay, B. V. Davies, S. A. Walters, P. D. Cole, T. E. Christopher, E. P. Joseph

Research output: Chapter in Book/Report/Conference proceedingChapter (peer-reviewed)peer-review

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After more than three months of lava dome extrusion, La Soufrière (St Vincent) transitioned to a series of explosive eruptions in April 2021. Here we present a time-series petrologic analysis of the phenocryst and microlite populations during the first c. 48 h of explosivity to constrain ascent conditions and processes that drove changes in behaviour. Primary eruptive products were crystal-rich (45–50 vol%) basaltic andesites with similar phenocryst phase assemblages and compositions. The change in eruptive style is consistent with over-pressurization as a consequence of second boiling from anhydrous microlite crystallization. The microlites display variation between the explosive phases, with two populations: (1) ‘inherited’ − normally zoned high-An plagioclase (>An 70) + olivine (Fo 62–79) + clinopyroxene + titanomagnetite, inferred to have crystallized at depths >15 km and high water pressures; (2) ‘juvenile’ − unzoned plagioclase (An 45–65) + clinopyroxene + orthopyroxene + intermediate pyroxene (Wo 12–38) + titanomagnetite, inferred to have crystallized upon ascent due to decompression and degassing. Scoria from the first explosions featured extensive groundmass crystallization and a significant ‘inherited’ microlite population. Later explosions had a more abundant ‘juvenile’ microlite population and lower crystallinity, consistent with more rapid ascent from depth, initiated by decompression following initial blasts and destruction of the lava dome.

Original languageEnglish
Title of host publicationThe 2020-2021 Eruption of La Soufriere Volcano, St Vincent
EditorsR. E. A. Robertson, E. P. Joseph, J. Barclay, R. S. J. Sparks
PublisherGeological Society of London
Number of pages30
Publication statusPublished - 1 Apr 2024

Publication series

NameGeological Society Special Publications

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