HR: 0800h
AN: T21B-0529    [Abstracts]
TI: Tomographic simulation of cold hydrous plumes above slabs
AU: Capel, A M
EM: allison@msi.umn.edu
AF: Department of Geology and Geophysics, Minnesota Supercomputing Institute, University of Minnesota, Minneapolis, MN 55455 United States
AU: * Yuen, D
AF: Department of Geology and Geophysics, Minnesota Supercomputing Institute, University of Minnesota, Minneapolis, MN 55455 United States
AU: Gerya, T
EM: taras.gerya@erdw.ethz.ch
AF: Geologisches Institut, Swiss Federal Institute of Technology, Zurich, 8092 Switzerland
AU: Connolly, J
EM: james.connolly@erdw.ethz.ch
AF: Geologisches Institut, Swiss Federal Institute of Technology, Zurich, 8092 Switzerland
AB: We have calculated the hetergeneous seismic velocity fields taken from numerical modeling of thermal-chemical plume structures above subducting slabs, using 50 million active tracers. Our 2-D numerical model of subduction zones combines the effects of thermal-chemical buoyancy as well as the effects of both hydration and melting. Numerical modeling suggests that partially molten hydrated upwellings above the subduction slab can produce a colder thermal anomaly of 300 to 400 degrees within the mantle wedge! Due to an assortment of crustal rocks and penetration of aqueous fluids, cold plumes may have an upward velocity greater than one meter per year. Initiation of these plumes is most likely due to massive release of water from a subducting slab due to putrefaction of serpentine at depths greater than 100 kilometers. The seismic velocities are computed from a thermodynamic model that accounts for phase transitions. These include melting, for the various lithologies of interest including dry and hydrated mantle, sediments, as well as basaltic and gabbroic oceanic crust. The model provides estimates for the proportions, compositions and seismic velocities of the stable phases as a function of pressure and temperature. Aggregate seismic velocities are computed using the Voight-Reuss-Hill averaging scheme. According to our simulation of 2-D seismic velocity field during the propagation of hydrated but cold plumes, water and temperature will interact producing either positive or negative seismic anomalies depending on water/temperature ratios. These ratios cause the seismic signal to change during plume propagation with positive anomaly been characteristic for the area of cold plume initiation close to the slab.
DE: 8100 TECTONOPHYSICS
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting