Towards a Physical Understanding of the Effects of Depth-dependent Rheology on Mantle Convection

Details Towards a Physical Understanding of the Effects of Depth-dependent Rheology on Mantle Convection Towards a Physical Understanding of the Effects of Depth-dependent Rheology on Mantle Convection

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.s11g..06r&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #S11G-06

Physics

8120 Dynamics Of Lithosphere And Mantle: General, 8121 Dynamics, Convection Currents And Mantle Plumes, 8124 Earth'S Interior: Composition And State (Old 8105), 8147 Planetary Interiors (5430, 5724)

Scientific paper

It has long been suspected that the presence of a low viscosity zone (LVZ) beneath (at least) the oceanic plates has a major influence on plate tectonics and mantle convection, and there is ample evidence for an LVZ from glacial rebound and geoid studies, seismology, and mineral physics. 3-D numerical studies of mantle convection show that an LVZ is very effective in promoting long-wavelength structure, and that an LVZ facilitates plate-like surface motions when coupled with a lithospheric failure rheology. However, a fluid mechanical understanding of these important effects has been elusive. Referring to an idealized conceptual model that exploits the symmetry of bottom-heated convection with LVZ's at both the top and bottom boundary layers, we have devoloped complementary theoretical models that elucidate the numerical results. Straightforward modification of classical boundary layer theory suggests that reduced horizontal shear stresses due to an LVZ should promote long-wavelenth structure. Rigorous scaling analysis can roughly predict the form and amplitude of the dependence of Nusselt number on Rayleigh number and horizontal wavelength, as revealed by 2-D numerical models of thermal convection. Extension of this analysis to non-symmetrical cases with internal heating and a single LVZ should be possible, and may lead to a more fundamental understanding of plate tectonics on Earth, and the lack thereof on Venus and Mars.

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