Computer Science
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....4502z&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #4502
Computer Science
Scientific paper
Core formation is generally thought to have occurred during or soon after planet formation. It therefore determines the initial conditions for thermal evolution models to a significant extent. A possible scenario for the formation of a planetary core would be the settling of iron-rich melt diapirs in a solid matrix. Assuming that a planet in the late stage of accretion has a magma ocean, there soon will form a layer of molten iron at the bottom of the magma ocean. Since the iron has a higher density than the underlying planetary mantle, it may sink in a Rayleigh--Taylor instability. Because the viscosity contrast is essentially infinite, the sinking melt diapir will take the shape of a sphere. We have modelled the Stokes falling of an iron sphere through a silicate mantle with temperature dependent viscosity using a 2-D finite element program (FEATFLOW) written by S. Turek. We solve the incompressible Navier--Stokes equation coupled with the energy and mass conservation equations. From these models the effect of the temperature dependence of the silicate rock viscosity on the sinking rate can be estimated. Depending on the diapir temperature, the temperature of the surrounding material and the reference viscosity, the drag force exerted on the diapir will be reduced by up to a few orders of magnitude. By equating the drag force with the body force the terminal velocity of the sinking diapir can be calculated. For a viscosity contrast of ν∞/ν_0 of 10^3 or more the terminal velocity can be increased by a factor of twenty with respect to the isoviscous case with ν = ν∞. To further increase core formation rate it may help to include the stress or pressure dependence of the rock rheology.
Spohn Tilman
Ziethe Ruth
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