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GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L12S09, doi:10.1029/2006GL025717, 2006

Dynamic effects of a step-wise increase in thermal conductivity and viscosity in the lowermost mantle

John B. Naliboff

Geology Department, University of California, Davis, California, USA


Louise H. Kellogg

Geology Department, University of California, Davis, California, USA


Abstract

We present numerical models of mantle convection incorporating changes in viscosity and thermal conductivity at depth. Increasing the viscosity and/or thermal conductivity by a factor of 5 at depths below 2000 km increases the size and stability of thermal upwellings. Decreasing the thermal conductivity beneath 2000 km, in contrast, has comparatively little effect on thermal upwellings. Increases in viscosity and/or thermal conductivity close to a factor of 5 beneath 2000 km may tend to counteract the tendency of the post-perovskite phase transition to decrease the size and stability of thermal upwellings. We also find that varying viscosity and thermal conductivity beneath 2000 km affects basal heat fluxes and mantle geotherms, which should have strong implications for the stability of the post-perovskite phase change near the core-mantle boundary (CMB).

Received 9 January 2006; accepted 15 March 2006; published 19 April 2006.

Index Terms: 8121 Tectonophysics: Dynamics: convection currents, and mantle plumes; 8124 Tectonophysics: Earth's interior: composition and state (1212, 7207, 7208, 8105); 8125 Tectonophysics: Evolution of the Earth (0325); 8130 Tectonophysics: Heat generation and transport.

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Citation: Naliboff, J. B., and L. H. Kellogg (2006), Dynamic effects of a step-wise increase in thermal conductivity and viscosity in the lowermost mantle, Geophys. Res. Lett., 33, L12S09, doi:10.1029/2006GL025717.