Marie-Noëlle Guilbaud

The AD 1250 El Metate shield volcano (Michoacán): Mexico’s most voluminous Holocene eruption and its significance for archaeology and hazards

The Michoacán–Guanajuato Volcanic Field is the largest subduction-related monogenetic volcanic field in the world and includes more than 1000 scoria cones and a few hundred medium-sized volcanoes. Although medium-sized volcanoes (domes and shields) are less abundant, hazards associated with the renewal of this type of activity should not be neglected. Here, we focus on El Metate volcano, the morphologically youngest shield of the field. This volcano has a minimum volume of ~9.2 km3 DRE, and its viscous lava flows were emplaced during a single eruption over a period of ~30 years covering an area of 103 km2. El Metate is thus best labeled as a monogenetic andesite shield. This eruption had a significant impact on the environment (modification of the hydrological network, forest fires, etc.), and hence, nearby human populations probably had to migrate. New C14 dates for the eruption yield a young age (~AD 1250), which briefly precedes the initial rise of the Tarascan Empire (AD 1350–1521) in this region. By volume, this is certainly the largest eruption during the Holocene in the Trans-Mexican Volcanic Belt, and it is the largest andesitic effusive eruption known worldwide for this period. Such a large volume erupted in a relatively short time bears important implications for evaluating future hazards in the Michoacán–Guanajuato Volcanic Field.

Insight into monogenetic eruption processes at Pelagatos volcano, Sierra Chichinautzin, Mexico: a combined melt inclusion and physical volcanology study

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