HR: 18:00h
AN: U44A-07    [Abstracts]
TI: Potential Dynamical Mechanisms Behind Global Mantle Events
AU: * Hansen, U
EM: hansen@earth.uni-muenster.de
AF: Insitute for Geophysics, Muenster University, Corrensstr. 24, Muenster, 48149, Germany
AU: Loddoch, A
AF: Insitute for Geophysics, Muenster University, Corrensstr. 24, Muenster, 48149, Germany
AU: Stein, C
AF: Insitute for Geophysics, Muenster University, Corrensstr. 24, Muenster, 48149, Germany
AB: By numerical models we have investigated three potential mechanisms behind global mantle events. Plumes, originating in the thermal boundary layers of the mantle convection system can exhibit a significant episodicity, once a strong temperature-dependence of the viscosity of the mantle material is taken into account. An increase of the viscosity with pressure, as sometimes believed to suppress plumes, acts in fact to focus buoyancy into a few strong upwellings, which are potentially able to generate events on global scale. Plumes originating self- consistently from a thermal boundary layer, transport mostly material from their source region, while they entrain only little material during ascent. Compositionally dense material at the Core-mantle boundary has been proposed to explain seismological observed anomalies. The stability of such heterogeneities against entrainment by the overlying mantle-flow is determined by a complex set of properties, rather than by the density difference alone. Model calculations, taking into account a combined dependence of viscosity on temperature, pressure and , as mostly neglected; on composition, demonstrate, that under such conditions the D", can function as an isolated reservoir form some time, that however the destruction of the compositionally distinct layer, shielding the Earth'core can take place rapidly., with a profound effect also on the surface heat flow.. Finally we observe that episodic mobilization events of the surface are dynamically plausible for appropriate rheologies. A combination of temperature- and stress-dependent viscosity leads to an intermittent type of temporal behavior, where periods showing no surface motion (stagnant lid) are interrupted by phases with strong plate motions at the top. It seems at least possible that plate motion is not a continuously operating process.
DE: 1212 Earth's interior: composition and state (7207, 7208, 8105, 8124)
DE: 8125 Evolution of the Earth (0325)
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
SC: Union [U]
MN: 2007 Joint Assembly