Dynamical consequences of depth-dependent thermal expansivity and viscosity on mantle circulations and thermal structure

Details Dynamical consequences of depth-dependent thermal expansivity and viscosity on mantle circulations and thermal structure Dynamical consequences of depth-dependent thermal expansivity and viscosity on mantle circulations and thermal structure

May 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993pepi...77..205h&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 77, Issue 3-4, p. 205-223.

Physics

69

Scientific paper

The effects of both depth-dependent thermal expansivity and depth-dependent viscosity on mantle convection have been examined with two-dimensional finite-element simulations in aspect-ratio ten boxes. Surface Rayleigh numbers between 107 and 6 × 107 have been considered. The effects of depth-dependent properties, acting singly or in concert, are to produce large-scale circulations with a few major upwellings. The interior of the mantle is cooled by the many cold instabilities, which are slowed down and eventually swept about by the large-scale circulation. The interior temperature of the mantle can be influenced by the trade-off between depth-dependent properties and internal heating. For chondritic abundance of internal-heating and depth-dependent thermal expansivity, the viscosity increase across the mantle can be no greater than a factor of around ten in order to keep the lower mantle adiabatic. The thermal contrasts between the cold blobs and the surrounding mantle are strongly reduced by depth-dependent properties, whereas the lateral differences between the hot upwelling and the ambient lower mantle can be significant, over several hundred degrees. Depth-dependent properties also encourage the formation of a stronger mean-flow in the upper mantle, which may be important for promoting long-term polar motions.

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