HR: 0800h
AN: U41B-0414    [Abstracts]
TI: Toward understanding Ultra Low Velocity Zone dynamics
AU: * McNamara, A K
EM: allen.mcnamara@asu.edu
AF: Arizona State University, School of Earth and Space Exploration, Tempe, AZ 85287, United States
AU: Garnero, E J
EM: garnero@asu.edu
AF: Arizona State University, School of Earth and Space Exploration, Tempe, AZ 85287, United States
AU: Rost, S
EM: s,rost@leeds.ac.uk
AF: University of Leeds, School of Earth and Environment, Leeds, LS2 9JT, United Kingdom
AB: The Ultra Low Velocity zone (ULVZ) is characterized by a sharp drop in seismic velocities in certain regions of the lowermost mantle. Furthermore, recent seismic observations indicate that the ULVZ may have a morphology of small kilometer-scale packets of anomalous material with a very high density increase. Potential explanations for the cause of the ULVZ include the presence of partial melt and/or fine-scale chemical heterogeneity (possibly due to iron enrichment). A fundamental question regarding both hypotheses pertains to whether mantle convection is dynamically capable to support such small-scale, high-density structures. We perform high-resolution, whole-mantle thermochemical convection calculations to test the feasibility of this hypothesis. We find that convection acts to segregate and support very thin layers of ultra-dense material into shapes that resemble seismic models. In addition, we test whether ultra-dense material, over the lifetime of the Earth, created in the lowermost few kilometers of the mantle can be collected into volumes similar to that of proposed thermochemical piles beneath Africa and the Pacific. Our results indicate that this is possible if the lowermost 2-5 km of the mantle is continually being injected with higher density material, possibly iron from the core.
DE: 7200 SEISMOLOGY
DE: 8100 TECTONOPHYSICS
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8125 Evolution of the Earth (0325)
SC: Union [U]
MN: 2007 Fall Meeting