HR: 09:45h
AN: U41A-08    [PDF]
TI: Dynamically Causes and Consequences of an Ultralow Viscosity Zone
AU: * Hansen, U
EM: hansen@earth.uni-muenster.de
AF: Inst. of Geophysics, Correnstr.24, Muenster, 48149 Germany
AB: The Core-Mantle-Boundary may be viewed in a first order approach as the thermal boundary layer of the convecting lower mantle. Many studies have, however, indicated structures which deviate from those, as expected from a 'simple' thermal boundary layer. Chemically induced density differences have been assumed to explain the various phenomena, ranging from observed topography of the Core-Mantle-Boundary to the existence of a zone characterized by an ultra-low viscosity. Chemically induced contributions to both, density and viscosity can basically arise by either a recharge of the material at the CMB through subducting slabs or through interactions of the mantle and the core leading to a material exchange between both systems. I a series of two- and three-dimensional numerical experiments, possible dynamical causes of an ultra-low viscosity zone were investigated. Especially the case of a chemically dense layer, resulting from interactions with the core, together with viscosity depending on temperature and composition is explored. This configurations leads to the existence of a layer of low viscosity on top of the Core-Mantle-Boundary. Further the influence of radioactive elements, depth dependence of the thermal expansion coefficient and also of pressure dependence of the viscosity, on the stability and on the temporal evolution of this ultra-low viscosity layer has been studied. ~ ~ ~
DE: 1015 Composition of the core
DE: 3924 High-pressure behavior
DE: 7207 Core and mantle
DE: 8115 Core processes (1507)
DE: 8124 Earth's interior--composition and state (old 8105)
SC: U
MN: 2003 Fall Meeting