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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy (S) - IASPEI - International Association of Seismology and Physics of the Earth's Interior JSS011 2093 - 2186 Symposium Earth Structure and Geodynamics Convener : Prof. Thorne Lay Integrated theoretical, observational and experimental studies involving seismology, geodynamics and geomagnetism are essential for advances in understanding of the dynamics of our planet. Fundamental problems such as the driving mechanisms for plate tectonics, the fate of subducted slabs, the role of water in the transition zone, the existence and nature of any mantle plumes, the isolation of geochemical reservoirs in the mantle, the structure and processes in the lowermost mantle boundary layer, and the chemical and physical interactions between the core and mantle all require multidisciplinary approaches. These topics will all be addressed in this symposium. Seismology provides constraints on the structure and amplitudes of heterogeneity in elastic properties and density and on elastic anisotropy using many imaging and modeling approaches. Geodynamics provides insights on the thermo-chemical nature of mantle convection, boundary layer behavior, interaction of flow with phase transitions, time evolution, and deformation processes using numerical modeling and laboratory experiments. These two fields interact closely, combined with constraints from mineral physics, geochemistry and geomagnetism to develop quantitative understanding of how the planet works. Both disciplinary and multidisciplinary papers drawing from these fields are invited for this symposium. This symposium will be subdivided into 5 multidisciplinary sessions: 1) lithosphere and asthenosphere structure and processes (L) 2) subduction zones and deep slabs (S) 3) mantle upwellings and plumes (P) 4) transition zone structure (T) 5) D" and mantle-core interactions (MC)

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy (S) - IASPEI - International Association of Seismology and Physics of the Earth's Interior JSS011 Oral Presentation 2093 Continental growth and preservation of geochemical mantle heterogeneity in spite of whole-mantle convection Prof. Uwe Walzer Institut f. Geowissenschaften Friedrich-Schiller-Universitaet Jena IASPEI Roland Hendel, John. Baumgardner The focus of this paper is the numerical simulation of the chemical differentiation of the Earth's mantle. This differentiation induces the generation and growth of the continents and, as a complement, the formation and augmentation of the depleted MORB mantle. Here, we present a solution of this problem by an integrated theory in common with the problem of thermal convection in a 3-D compressible spherical-shell mantle. The conservation of mass, momentum, energy, angular momentum, and of four sums of the number of atoms of the pairs 238U-206Pb, 235U-207Pb,232Th-208Pb, 40K-40Ar is guaranteed by the used equations. The whole coupled thermal and chemical evolution of mantle plus crust was calculated starting with the formation of the solid-state primordial silicate mantle. No restricting assumptions have been made regarding number, size, form, and distribution of the continents. It was, however, implemented that moving oceanic plateaus touching a continent are to be accreted to this continent at the corresponding place. The model contains a mantle-viscosity profile with a usual asthenosphere beneath a lithosphere, a highly viscous transition zone and a second lowviscosity layer below the 660-km mineral phase boundary. The central part of the lower mantle is highly viscous. This explains the fact that there are, regarding the incompatible elements, chemically different mantle reservoirs in spite of perpetual stirring during more than 4.49 billion years. The highly viscous central part of the lower mantle also explains the relatively slow lateral movements of CMB-based plumes, slow in comparison with the lateral movements of the lithospheric plates. The temperature- and pressure-dependent viscosity of the model is complemented by a viscoplastic yield stress, Sy. The paper includes a comprehensive variation of parameters, especially the variation of the viscosity-level parameter, rn, the yield stress, Sy, and the temporal average of the Rayleigh number. In the rn-Sy plot, a central area shows runs with realistic distributions and sizes of continents. This area is partly overlapping with the rn-Sy areas of piecewise plate-like movements of the lithosphere and of realistic values of the surface heat flow and Urey number. Keywords: mantle convection, continental growth, chemical heterogeneity

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