Petrologic evidence for pressure-temperature conditions and recent reheating of andesitic magma erupting at Soufriere Hills Volcano, Montserrat, WI

J. D. Devine, M. D. Murphy, M. Rutherford, J. Barclay, R. S. J. Sparks, M. R. Carroll, S. R. Young, J. E. Gardner

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The recent eruption of the Soufriere Hills Volcano in Montserrat (July, 1995, to present; September, 1997) has produced an andesitic dome (SiO2 ∼ 59–61 wt.%). The eruption has been caused by invasion of mafic magma into a preexisting andesitic magma storage region (P ∼ 130 MPa; ≥5 km depth). The composition of the andesite has remained essentially constant throughout the eruption, but heating by the mafic magma increased the andesite temperature from ≤830°C to ≤880°C. Prior to being heated, the stable mineral assemblage in the andesite was plagioclase + amphibole + orthopyroxene + titanomagnetite + ilmenite + quartz. The rise in temperature from ≤830°C to ≤880°C (fO2 ∼ 1 log unit above NNO) has caused quartz to become unstable, and has also caused changes in silicate and Fe-Ti oxide mineral compositions. The andesitic magma is likely saturated with an H2O-rich vapor phase in the upper part of the magma storage region. Melt H2O content is ∼4.7 wt.%.
Original languageEnglish
Pages (from-to)3669-3672
Number of pages4
JournalGeophysical Research Letters
Issue number19
Publication statusPublished - 1 Oct 1998

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