Layered convection with an interface at a depth of 1000km: stability and generation of slab-like downwellings

Details Layered convection with an interface at a depth of 1000km: stability and generation of slab-like downwellings Layered convection with an interface at a depth of 1000km: stability and generation of slab-like downwellings

Apr 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004pepi..141..269c&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 141, Issue 4, p. 269-279.

Physics

3

Scientific paper

We investigate the stability of hypothetical layered convection in the mantle and the mechanisms how the downwelling structures originating in the lower layer are generated. The stability is studied by means of numerical simulations of the double-diffusive convection in a 2D spherical model with radially dependent viscosity. We demonstrate that the stability of the layering strongly depends not only on the density contrast between the layers but also on the heating mode and the viscosity profile. In the case of the classical Boussinesq model with an internally heated lower layer, the density contrast of about 4% between the compositionally different materials is needed for the layered flow to be maintained. The inclusion of the adiabatic heating/cooling in the model reduces the temperature contrast between the two layers and, thus, enhances the stability of the layering. In this case, a density contrast of 2-3% is sufficient to preserve the layered convection on a time scale of billions of years. The generation of the downwelling structures in the lower layer occurs via mechanical or thermal coupling scenarios. If the viscosity dependent on depth and average temperature at each depth is considered, the low viscosity zone develops at a boundary between the two convecting layers which suppresses mechanical coupling. Then the downwelling structures originating in the lower layer develop beneath upper layer subductions, thus resembling continuous slab-like structures observed by seismic tomography.

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