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U. Walzer, T. Burghardt, R. Hendel (University Jena)
The first part of this investigation refers to the theory and numerical simulations of solid-state convection of the Martian mantle. Available structural models of Mars have been critically studied to receive a basic model for our dynamical calculations of the Martian spherical-shell mantle. We newly derived thermal expansivity, activation volume, activation energy, Gruneisen parameter, melting temperatures, shear viscosity, and other physical parameters. Different sets of the distribution of the mentioned quantities result in different types of the convection planforms as a function of viscoplastic yield stress, Rayleigh number, Nusselt number and Urey number. Only in a few cases, we obtain an early Martian plate tectonics and the transfer to a one-plate planet.
For comparison we present our results for solid-state convection of the Earth's mantle solving the full set of balance equations, too. The pressure, P, the bulk modulus, K, and dK/dP of the seismic model PREM were used to derive the Gruneisen gamma. The viscosity was calculated from the Gilvarry formulation of Lindemann's law, some solid-state physics and the Haskell value of subcontinental viscosity. The new terrestrial viscosity profile, called eta3, shows a high-viscosity transition layer with steep viscosity gradients at its boundaries, a second low-viscosity layer under the 660-km discontinuity, and a strong viscosity increase in the central part of the lower mantle. The Newtonian rheology is supplemented by a viscoplastic yield stress. For a medium-sized Rayleigh-number--yield-stress area, eta3 generates a stable, plate-tectonic behaviour near the surface and simultaneously thin sheet-like downwellings in the depth.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.