HR: 17:15h
AN: U44A-06    [Abstracts]
TI: Using a New Multi-Discipline Approach to Predict Seismic Tomography from Geodynamical Models of Mantle Convection
AU: * Bull, A L
EM: abigail.bull@asu.edu
AF: School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, United States
AU: McNamara, A K
EM: allen.mcnamara@asu.edu
AF: School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, United States
AU: Ritsema, J
EM: jritsema@umich.edu
AF: Department of Geological Sciences, The University of Michigan, Ann Arbor, MI 48109, United States
AU: Lithgow-Bertelloni, C
EM: crlb@umich.edu
AF: Department of Geological Sciences, The University of Michigan, Ann Arbor, MI 48109, United States
AU: Stixrude, L
EM: stixrude@umich.edu
AF: Department of Geological Sciences, The University of Michigan, Ann Arbor, MI 48109, United States
AB: Understanding the first-order dynamical and compositional structure of Earth's mantle is a fundamental goal in solid-earth geophysics. Rudimentary knowledge of mantle structure relies on observations from geochemistry and seismic tomography and on inferences from theoretical convection models. Seismic tomography has shown the lower mantle to be dominated by a long-wavelength lateral velocity structure, characterized by broad low shear-wave velocity anomalies beneath Africa and the Central Pacific. Mantle convection models which describe the lower mantle as homogeneous explain the anomalies as clusters of small thermal plumes in an isochemical mantle while heterogeneous mantle models place the anomalies into the context of thermochemical piles characterized by an anomalously dense chemical component. Direct comparisons of temperature fields from theoretical calculations to the observed global shear-wave seismic tomography models suggest that models of thermochemical convection better recreate the lower mantle velocity structure however significant differences in the resolution of seismic and geodynamic models complicate such direct comparison. The parameterization of tomographic models is an order of magnitude larger than that of the numerical models, and the former are inherently spatially heterogeneous. Consequently, tomographic models distort heterogeneities, resulting in a blurred image of mantle structure. It is therefore plausible that the anomalies are poorly-imaged clusters of thermal plumes and not dense piles as consensus suggests, reopening the possibility of isochemical convection as being the mode of heat and mass transport which characterizes Earth's mantle. Using a new multi- discipline technique based on first-principle mineral physics, we perform calculations to predict seismic tomography from theoretical geodynamical models. We investigate whether seismic observations can be used as a constraint to distinguish between numerical models of plume clusters in an isochemical mantle and thermochemical piles in a chemically heterogeneous mantle as possible causes of the seismically observed lower mantle velocity structure. We find that our geodynamically predicted tomographic images differ significantly from the original numerical temperature fields, suggesting that the difference in resolution between seismic models and theoretical models is an important parameter to take into account when investigating lower mantle structure.
DE: 0545 Modeling (4255)
DE: 1011 Thermodynamics (0766, 3611, 8411)
DE: 3900 MINERAL PHYSICS
DE: 7270 Tomography (6982, 8180)
SC: Union [U]
MN: 2007 Fall Meeting