HR: 0800h
AN: T31A-1265    [Abstracts]
TI: Particular Mantle Dynamics Induced by Continental Roots
AU: * Perry, H
EM: perry@ipgp.jussieu.fr
AF: Laboratoire de Dynamique des Systemes Geologiques, Institut de Physique du Globe de Paris, Paris, 75252 France
AU: Jaupart, C
EM: jaupart@ipgp.jussieu.fr
AF: Laboratoire de Dynamique des Systemes Geologiques, Institut de Physique du Globe de Paris, Paris, 75252 France
AU: Tackley, P
EM: ptackley@ess.ucla.edu
AF: Department of Earth and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095-1567 United States
AB: Continental roots represent extensive regions of seismically fast, cold and chemically buoyant material compared to the surrounding mantle. These thick masses may affect circulation in the mantle and impart thermal conditions at their base which determine to some extent the style of convection. A 2-D Cartesian viscous flow model in which the mantle and lithosphere are described as compressible, Newtonian fluids is used. The continental root is sufficiently viscous such that it does not deform. A range of realistic Rayleigh Numbers are considered. The mantle is internally heated and heat production by the decay of radioactive elements U,K,Th in the lithosphere is incorporated into the model. The amount of continental heat production determines the thickness of the continental thermal boundary layer, and in turn the amplitude of lateral temperature anomalies between oceans and continents. Vertical temperature gradients beneath continents are significantly super-adiabatic with a thick thermal basal boundary layer. The thickness of this basal thermal boundary layer and the amplitude of lateral temperature anomalies determines to what extent continents affect deep mantle circulation below and around the root. We characterize families of solutions in which, depending on the heat production in the continental lithosphere, continents either alter mantle circulation below them or are displaced over time without imposing significant disruption on the mantle dynamic system. Differentiating between the two types of solutions may help to understand the evolution of mantle temperatures and dynamics over geologic time.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8125 Evolution of the Earth
DE: 8130 Heat generation and transport
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting