HR: 1330h
AN: T32B-0928    [PDF]
TI: Thermochemical Structures Within a Spherical Mantle: Superplumes or Piles?
AU: * McNamara, A K
EM: mcnamar@colorado.edu
AF: University of Colorado, Department of Physics, 390 UCB, Boulder, CO 80309-0390 United States
AU: Zhong, S
EM: szhong@spice.colorado.edu
AF: University of Colorado, Department of Physics, 390 UCB, Boulder, CO 80309-0390 United States
AB: Heterogeneous compositional mantle models are frequently invoked to explain some observations obtained from geochemistry and seismology. In particular two regions in the Earth's lower mantle - under the Pacific and Africa - are often interpreted as being either piles or superplumes of dense material. We perform numerical modeling of thermochemical convection in a three-dimensional spherical geometry to investigate whether the presence of a dense chemical component can lead to the formation of rounded piles or superplumes of material. In addition, we investigate whether a dense component can lead to degree-two structure, leading to two distinct thermochemical features. We study the effect of temperature and compositionally-dependent viscosity, and we find 2 different modes of dense layer deformation. Temperature-dependent rheology leads to a low viscosity dense layer which is passively swept aside by downwellings into linear piles spread throughout the entire lower mantle. The addition of compositionally- dependent rheology in which the dense layer is more viscous, results in active deformation of the dense material, forming large isolated superplumes. Our results indicate that piles and superplumes are separate features which in general, do not occur together, and in order for isolated,rounded superplumes to form, an intrinsic compositional viscosity increase is required for the dense material.
DE: 8100 TECTONOPHYSICS
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: 8162 Rheology--mantle
SC: Tectonophysics [T]
MN: 2003 Fall Meeting