HR: 0800h
AN: V41D-0794    [Abstracts]
TI: Pre-eruptive Volatile Contents of Mafic Magma at Popocatépetl Volcano, Mexico, from Olivine- hosted Melt Inclusions
AU: * Roberge, J
EM: roberge@geofisica.unam.mx
AF: Laboratorio Universitario de Petrología, Instituto de Geofisica UNAM, Ciudad Universitaria, Coyoacán, Mexico, D.F 04510, Mexico
AU: Delgado-Granados, H
EM: hugo@geofisica.unam.mx
AF: Laboratorio Universitario de Petrología, Instituto de Geofisica UNAM, Ciudad Universitaria, Coyoacán, Mexico, D.F 04510, Mexico
AU: Wallace, P J
EM: pwallace@uoregon.edu
AF: Department of Geological Sciences, University of Oregon, 1272 University of Oregon, Eugene, OR 97403-1272, United States
AU: Kent, A J
EM: adam.kent@geo.oregonstate.edu
AF: Department of Geosciences, Oregon State University, 104 Wilkinson Hall, Oregon State University, Corvallis, OR 97330, United States
AB: Volcanic gases are intimately related to degassing and their study allows the characterization of the composition, concentration and origins of volatiles in magma. Exsolution and loss of volatiles, particularly H₂O, CO₂ and S, leads to major changes in magma crystal content, density and viscosity, which in turn can produce major shifts in eruption style (explosive to dome building). Therefore understanding degassing behavior at active volcanoes is crucial for hazard evaluation. Gas emissions at active volcanoes (mainly SO₂), has commonly been attributed to dissolved sulfur in the silicate melt before eruption. However, for most eruptions for which remote sensing and melt inclusion data are available, excess eruptive S in gas emissions is observed so a pre-eruptive gas phase could be another source of sulfur emissions (Wallace, 2001). We analyzed melt inclusions in Fo 88-90 olivine from the May 11 and June 30, 1997 eruptions of Popocatépetl (Mexico). The melt inclusions are basaltic trachyandesite in composition, with 3.17 - 5.30 wt% MgO and 50.32 - 54.75 wt% SiO₂. Analyses by FTIR and electron microprobe show that the melt inclusions contain 0.2 – 4.70 wt% H₂O, <100 - 2413 ppm CO₂, 624 - 2222 ppm S, and 821 – 1169 ppm Cl. Calculated vapor saturation pressures for these melt inclusions (<0.1 - 6 kb) demonstrate that degassing of mafic magma beneath Popocatépetl starts at a minimum depth of 25 km. In addition, the high dissolved CO₂ and S contents in the melt inclusions suggest that mafic magma recharges was responsible for the high measured fluxes of CO₂ and SO₂ at Popocatépetl during the period from April to June, 1997.
DE: 1043 Fluid and melt inclusion geochemistry
DE: 3640 Igneous petrology
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
DE: 8430 Volcanic gases
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting