HR: 09:45h
AN: G31A-08    [Abstracts]
TI: Mantle Dynamics and the Long-Term Rotational Stability of the Earth
AU: * Daradich, A L
EM: daradich@physics.utoronto.ca
AF: Department of Physics, University of Toronto, 60 St. George St., Toronto, ON M5S 1A7 Canada
AU: Mitrovica, J X
EM: jxm@terra.physics.utoronto.ca
AF: Department of Physics, University of Toronto, 60 St. George St., Toronto, ON M5S 1A7 Canada
AU: Matsuyama, I
EM: isamu@astro.utoronto.ca
AF: Department of Astronomy and Astrophysics, University of Toronto, 60 St. George St., Toronto, ON M5S 1A7 Canada
AU: Latychev, K
EM: latychev@physics.utoronto.ca
AF: Department of Physics, University of Toronto, 60 St. George St., Toronto, ON M5S 1A7 Canada
AU: Moucha, R
EM: moucha@physics.utoronto.ca
AF: Universite du Quebec a Montreal, GEOTOP - Departement des Sciences de la Terre et de l'Atmosphere, CP 8888, succursale Centre-Ville, Montreal, QC H3C 3P8 Canada
AB: The long term (10-100 Ma) rotational stability of a dynamic, evolving Earth is a classic problem in geophysics framed by a series of seminal studies (e.g., Gold, 1955; Goldreich and Toomre, 1969). Gold (1955), for example, considered the stability of a hydrostatic planet subject to an imperfectly compensated (internal or external) load. In this case, the hydrostatic bulge provides no long-term rotational stability and the reorientation of the pole, or so-called true polar wander (TPW), would be governed solely by the location of the load. In particular, a mass excess of any size (indeed, as small as Gold's beetle) would drive a TPW that would eventually reorient the load to the equator. Gold's (1955) arguments were extended by Goldreich and Toomre (1969) who demonstrated that a group of anomalous masses moving randomly on the surface (the classic set of scurrying beetles) could drive rapid (relative to the speed of the masses) reorientation of the rotation pole. This inherent instability of the rotation axis appears to be at odds with observational evidence for a relatively stable rotation axis over the last 200 Ma. Previous studies have attempted to explain this stability through some combination of a high viscosity (sluggish) lower mantle and/or a relatively fortuitous distribution of mantle heterogeneity. We will present a new set of predictions of long term TPW based on a suite of three-dimensional convection simulations initiated using seismically-inferred mantle heterogeneity. These simulations, which are constrained by recent estimates of the radial profile of mantle viscosity (Mitrovica and Forte, 2004) and which also incorporate the stabilizing influence of a heterogeneous lithosphere, yield a suite of simple conditions governing rotational stability in the post-Jurassic Earth.
DE: 1213 Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120)
DE: 1239 Earth rotation variations
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Geodesy [G]
MN: Fall Meeting 2005