HR: 08:45h
AN: V51B-03 INVITED     [Abstracts]
TI: Subducted lithosphere at the core-mantle boundary? Possible rheological and chemical consequences for the D" region.
AU: * Rushmer, T
EM: Tracy.Rushmer@uvm.edu
AF: Dept. of Geology, University of Vermont, Burlington, VT 05405, United States
AB: Recent studies using seismic tomography datasets and horizontally polarized shear waves (e.g. Hutko et al., Nature, v. 441, 332-337, 2006) have suggested that not only is the core-mantle boundary a complex rheological and chemical environment, but conclude that subducted lithosphere may ultimately be emplaced in the lowermost mantle, the D" region. Analyses of these data sets suggest that this region is significantly dynamic in terms of temperature variations, associated up- and downwellings and overall rheologic behavior. Mineral physics studies of high pressure transitions have added to the discussion of the core mantle boundary (CMB) region in terms of first discovering the post-perovskite phase which may help our understanding of observed seismic anisotropy in addition to modifying chemistry so that the area becomes enriched in Fe which in turn influences heat flux mechanisms. Among many key areas for study, is investigating the rheological behavior of perovskite/post-pervoskite during shear deformation and the possibility that during shear events outer core material may be entrained into D". Downwelling cold slabs may drive deformation in D" as they impinge directly upon the CMB and can set up transient shear environments. Early experimental results on post-perovskite analog material (Yamazaki et al., EPSL v. 252, 372-378), have shown that post-perovskite may deform by dislocation, not diffusion, creep. In a set of deformation experiments under high pressure, olivine and FeS responded such that molten FeS migrated into zones of relatively lower pressure, driven by transient pressure gradients set up while the material undergoing shear. Continued experimental study at high pressure integrated with observational sets of data and numerical modeling is critical in furthering our understanding of how slab penetration into D" determines the rheological and chemical heterogeneity currently observed in the D" region.
DE: 8162 Rheology: mantle (8033)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly