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Abstract

Eruptions and magma evolution of monogenetic volcanoes are thought to be controlled by rapid ascent of magmas over a short period of time. Volatiles degassing from magmas control the ascent velocity and therefore eruption intensity. Complex feedbacks exist between the rate and extent of volatile exsolution at shallow levels and groundmass crystallization, affecting the magma rheology, extent of fragmentation, resulting eruptive style and related hazards. Melt inclusions record the volatile contents and compositions of melts at various stages during their evolution, providing insights into degassing–crystallization processes at shallow crustal levels. Here we present new volatile and major element data from olivine-hosted melt inclusions from Pelagatos scoria cone, Mexico. These new data, combined with recent geochemical and textural data on Pelagatos eruptive products, allow us to propose a model for shallow magmatic processes at this volcano. Discharge of volatile-poor, low-viscosity magma drives early effusive activity along the fissure. Decreasing magma fluxes lead to the clogging of the fissure and the formation of a shallow magma reservoir where degassing and fractional crystallization take place. Subsequent explosive cone-forming activity is triggered by influx of deeper (c. 5 km), less evolved, more volatile-rich magma into this shallow (c. 1 km) reservoir.

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new whole rock and matrix glass date are available at www.geolsoc.org.uk/SUP18782.

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