Pressure- and temperature-dependent thermal expansivity and the effect on mantle convection and surface observables

Details Pressure- and temperature-dependent thermal expansivity and the effect on mantle convection and surface observables Pressure- and temperature-dependent thermal expansivity and the effect on mantle convection and surface observables

Jul 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003geoji.154..224s&link_type=abstract

Geophysical Journal International, Volume 154, Issue 1, pp. 224-229.

Astronomy and Astrophysics

Astronomy

9

Mantle Convection, Seafloor Topography, Thermal Expansivity

Scientific paper

In most mantle convection studies with variable thermal expansivity only the pressure dependence is considered. Here we investigate the effect of temperature- and/or pressure-dependent thermal expansivity α on the distribution of buoyancy forces in mantle convection. Thermal expansivity is calculated for the dominant upper-mantle mineral, forsterite, and a map of its dependence on T and p is given. By studying simple 2-D steady-state constant-viscosity convection and comparing cases with constant α, α(p), α(T) and α(p, T) we find that at mantle temperatures the pressure dependence of α is important. For the lithosphere the dependence of α on temperature dominates, since the temperature dependence of α is much stronger in the low-pressure regime. Also dynamic topography changes considerably (up to 15 per cent) if α is T- and p-dependent compared with a constant or only p-dependent case. Scaling laws for the Nusselt number and the rms velocity are obtained. They differ from the constant-α case by at most 12 per cent if an effective Rayleigh number based on the spatial average of α is used.

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