HR: 11:35h
AN: S11G-06    [PDF]
TI: Towards a Physical Understanding of the Effects of Depth-dependent Rheology on Mantle Convection
AU: * Richards, M
EM: markr@seismo.berkeley.edu
AF: Dept. of Earth and Planetary Science, University of California, Berkeley, CA 94707 United States
AU: Morris, S
EM: morris@newton.berkeley.edu
AF: Dept. of Mechanical Engineering, University of California, Berkeley, CA 94707 United States
AU: Busse, F
EM: Friedrich.Busse@uni-bayreuth.de
AF: Institute of Physics, University of Bayreuth, Bayreuth, D95440 Germany
AU: Lenardic, A
EM: adrian@esci.rice.edu
AF: Dept. of Earth Sciences, Rice University, Houston, TX 77251 United States
AB: 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.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 8147 Planetary interiors (5430, 5724)
SC: Seismology [S]
MN: 2003 Fall Meeting