HR: 1340h
AN: V33A-1461    [Abstracts]
TI: Implications of Viscosity-Contrast for Co-Extruding Two-Component Magmas, Triggering Eruptions and Forming Layered Domes
AU: * Carrigan, C R
EM: carrigan1@LLNL.gov
AF: Lawrence Livermore National Laboratory, (L-201) PO Box 808, Livermore, CA 94551 United States
AU: Clarke, S M
EM: stuart@bpi.cam.ac.uk
AF: BP Institute, Cambridge University, Madingley Road, Cambridge, CB3 0EZ United Kingdom
AB: Polymer co-extrusion experiments represent excellent dynamical analogies with two-magma transport and the effusion of composite lava domes. They demonstrate that the co-extrusion of magmas having different viscosity can explain not only the observed normal zoning in magma dikes and conduits but also the compositional layering observed in effused lava domes. New results indicate that dike and conduit zoning along with dome layering are strongly dependent on the viscosity contrast between the flowing magmas. Realistic models of magma storage and dike formation show that co-extrusion of magmas is both more readily explained and energetically preferred over serial intrusion processes. Co-extrusion during the formation of dikes may play an important role in triggering larger volcanic eruptions. Lubrication of the flow by a typically, more mafic, lower-viscosity component allows a more viscous but also more highly volatile-charged magma to be transported greater distances upward in the dike resulting in exsolution of a gas phase and the formation of a magma foam. Transition to a foam lowers the bulk density of the magma enabling dikes to propagate greater vertical distances for a given back pressure. Our new results suggest that a dike propagating across a sloping magma-chamber roof intersecting both "wet" silicic and relatively "dry" mafic layers has the greatest probability of reaching the surface in the dike segment where the magmas flow co-extrusively. Thus, bimodal eruptive compositions are dynamically preferred in such a petrologically common magmatic regime. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
DE: 8414 Eruption mechanisms
DE: 8429 Lava rheology and morphology
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting