HR: 1340h
AN: MR23A-0178    [Abstracts]
TI: THE DYNAMICS OF THE POST-PEROVSKITE BOUNDARY AS PORTRAYED BY THE SHALLOW-WATER EQUATIONS
AU: VIncent, A
EM: vincent@astro.umontreal.ca
AF: Univ. Montreal, Departement de Physique, Montreal, QC H3C 3J7 Canada
AU: * Yuen, D A
EM: davey@msi.umn.edu
AF: University of Minnesota, Dept. of Geology and Ggeophysics and Minnesota Supercomputing Institute, Minneaplois, MN 55455-0219 United States
AB: The recent discovery of the post-perovskite phase transition is indeed exciting from the perspective of fluid dynamics, because of its proximity to the core-mantle boundary (CMB). This situation raises some poignant issues about the traditional concept of a bottom thermal-boundary layer in mantle convection, because this new phase transition is, in fact, embedded inside the boundary layer itself. The steep Clapeyron slope of close to 10 MPa/K also raises the possibilities that the phase boundary may disappear altogther under regions of upwelling ,if there is a local increase of temperature by about 1000 K. Since the deflection of the phase boundary is O(50 km), as compared to the typical wavelengths of lower-mantle convection above the phase transition, we have made use of the shallow-water equation by invoking the hydrostatic ansatz and accounting only for the vertical momentum and heat-transfer. We developed a set of 2-D cartesian equations in the long-horizontal wavelength limit for the position of the phase boundary h(x,t), v(x,t) the horizontal velocity , and T(x,t), the temperature perturbation from the background temperature profile in the deep mantle, where t is time and x is a horizontal coordinate above the CMB. The set of nonlinear PDE's consisted of two initial-value nonlinear coupled partial differential equations and is an initial-boundary-value problem for T and h and one elliptic PDE for v. The time-derivative of h is the dominant coupling to both the PDE's governing T and v. There are four dimensionless parameters governing this system: S ,which governs the density change of the transition; Rq , which is a measure of the latent-heat released, D, the dissipation number and Tc, a measure of the temperature difference between the CMB and the lower mantle above the D" layer. This formalism can be extended to chemical variations in the D" layer. We can also take into account 3-D and spherical geometries, thus paving the road for an efficient computational means of matching the mantle convection solution to the core dynamics in the face of the post-perovskite phase change.
DE: 8121 Dynamics, convection currents and mantle plumes
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting