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

Holli M. Frey*, Matthew R. Manon, Jenni Barclay, Bridie V. Davies, Sydney A. Walters, Paul D. Cole, Thomas E. Christopher, Erouscilla P. Joseph

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

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 ∼48 hours of explosivity to constrain ascent conditions and processes that drove changes in behavior. 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 overpresurization 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 (>An70) + olivine (Fo62-79) + clinopyroxene + titanomagnetite, inferred to have crystallized at depths >15 km and high water pressures; 2) “juvenile” - unzoned plagioclase (An45-65) + clinopyroxene + orthopyroxene + intermediate pyroxene (Wo12-38) + 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
Pages (from-to)201-230
Number of pages30
JournalGeological Society, London, Special Publications
Volume539
Issue number1
Early online date5 Apr 2023
DOIs
Publication statusPublished - 1 Apr 2024

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