HR: 09:00h
AN: DI51B-06    [Abstracts]
TI: Mapping thermal and compositional variations in the mantle transition zone: Uncertainties due to the resolution of seismic observations
AU: * Shen, Y
EM: yshen@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, South Ferry Road, Narragansett, RI 02882, United States
AB: Seismic observations of the transition-zone discontinuities along with volumetric velocity variations in the transition zone are diagnostic of the thermal and compositional states of the mantle and associated dynamics. As high-pressure experiments and theoretical calculations provide more and more accurate constraints on the mantle phase relations and the elastic coefficients of likely minerals as a function of pressure, temperature, and composition, attempts have been made in recent years to quantitatively estimate thermal and compositional variations in the transition zone by solving the equations in which the discontinuity depths and volumetric velocity perturbations are expressed as a function of mantle temperature and composition. By integrating the constraints on the phase transitions and surrounding mantle, these studies were able to separate thermal anomalies and variations in water content in the transition zone. The estimates are, however, highly sensitive to the thermal and compositional dependence of the seismic parameters as well as the uncertainties of tomographic models and discontinuity depths, whose effects on mapping thermal and compositional variations in the transition zone are yet to be carefully assessed. I will present a re-analysis of the thermal and compositional states of the mantle transition zone beneath southern Africa. A finite-frequency tomography method, which takes into account of wavefront healing of realistic seismic waves, is used to obtain more robust P and S velocity models of the transition zone than in previous studies. The results will be compared to those based on ray theory and tested by comparing observed waveforms and simulations of full wave propagation in the 3D models. The finite-frequency velocity models will be used to re-calculate the discontinuity topography. The propagation of the uncertainties of the tomographic models and discontinuity depths to the estimates of the thermal and compositional variations will be discussed.
DE: 3924 High-pressure behavior
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7270 Tomography (6982, 8180)
DE: 8103 Continental cratons
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting