HR: 14:10h
AN: T52E-03    [PDF]
TI: Trapped Heat in the Mantle: The Origin for Topographic Flattening at Old Seafloor.
AU: Huang, J
EM: Jinshui.Huang@colorado.edu
AF: University of Colorado, Dept. of Physics, Boulder, CO 80309 United States
AU: * Zhong, S
EM: szhong@anquetil.colorado.edu
AF: University of Colorado, Dept. of Physics, Boulder, CO 80309 United States
AB: It is well known that the rates at which seafloor topography and heat flux vary with age are greatly reduced at old seafloor (i.e., flattening), compared with the predictions from the half space cooling model. The origin for the reduced rates remains unresolved. In the conventional plate model, plate cooling is arrested at old seafloor through sublithospheric small-scale convection (SSC) that removes the bottom part of lithosphere and homogenizes it with the underlying mantle, leading to a constant lithospheric thickness at old seafloor and reduced rates of variations in topography and heat flux with age. While recent surface-wave tomography studies in the Pacific provide evidence for SSC and its associated lithospheric structure, it has been long debated whether SSC leads to topographic flattening or deepening, given that SSC could cool the mantle more efficiently to give rise to a even colder mantle below old seafloor than that without SSC. We have formulated numerical models to examine the effects of SSC under a mobile plate on the seafloor topography. In models with flow-through boundary conditions that best mimic the cooling of initially hot flow and isolate the effects of SSC, We found over a large parameter space for mantle rheology and plate motion that SSC has little influence on the topography which undulates around but closely follows the prediction from the half-space cooling model. However, in more realistic models with significant internal heating in a closed box, we found that heat tends to accumulate below old lithosphere, leading to topographic flattening. The heat accumulation below old lithosphere occurs because the thick lithosphere results in less efficient heat transfer than that at young seafloor. When SSC is absent, the accumulated heat is distributed over a large depth range. However, SSC brings the heat to shallow depths below the thinned lithosphere and causes largely uniform temperature in the underlying mantle.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8150 Plate boundary--general (3040)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting