A numerical study of the effects of boundary conditions on mantle convection models constrained to fit the low degree geoid coefficients

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Abstract

A simple mathematical model is set up to study the effects on the mantle convection pattern of boundary conditions at the core-mantle boundary and at the surface (or the lithosphere-asthenosphere boundary). Uniform viscosity and homogeneous heat source are assumed and the density differences driving convection and the associated boundary undulations are constrained to fit the observed low degree geoid coefficients. The most important conclusion is that when the Rayleigh number is around 1.4–1.8 times the critical Rayleigh number at degree 2, a model having a free lower boundary and a frictional upper boundary gives plate motions strongly disagreeing with the observed motions, but a model with a free upper boundary and frictional lower boundary agrees better with the global tectonic features. In this case the frictional lower boundary is considered to represent increasing viscosity with depth, which is not formally included in the model. The correlation between convergent zones of the calculated convection pattern and the subducting slabs indicates that the slabs provide the most plausible driving mechanism of the plate motions.

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  • Cited by (0)

    On leave from Department of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui Province, Peoples Republic of China.

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