Viscosity structure implied by mantle convection

Details Viscosity structure implied by mantle convection Viscosity structure implied by mantle convection

May 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989pepi...55....1s&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 55, Issue 1-2, p. 1-9.

Physics

4

Scientific paper

The total mechanical dissipation by convective motion in the mantle is well constrained by thermodynamic arguments to ~ 5.6 × 1012 W. By adopting a simple convection model we can use the observed mean plate speed υ = 3.25 cm y-1 to estimate the mean mantle creep rate, ɛ˙ ~ 7.2 × 10 -16 s-1, which implies a mean effective stress σ ~ 8.5 × 106 Pa and a corresponding viscosity υ ⋍ 1.2 × 1022 Pa s. This viscosity estimate is biased low by the nature of the implied averaging, but for better estimates we must make assumptions about the internal convective pattern. If we assume that the convection is self-sustaining at all depths, and therefore that the depth distribution of dissipation is the same as the depth distribution of generated power, and that the convective pattern is self-adjusted to make stress independent of depth, then we can specify the mantle viscosity profile. These assumptions imply quasi-steady convection. The fact that viscosities inferred from convection are higher than values from isostatic rebound most plausibly arises as a difference between steady state and transient creep.

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