HR: 09:25h
AN: V41G-06    [Abstracts]
TI: Dynamics of flowline Hotspots
AU: * Sleep, N H
EM: norm@pangea.stanford.edu
AF: Department of Geophysics, Stanford University, Panama Mall, Stanford, CA 94305, United States
AB: Numerous linear chains of volcanoes are perpendicular to the isochrons of oceanic plates. As lithospheric thickness increases with plate age, these "flowline" hotspots are frequently attributed to the flow of buoyant plume material along the base of the lithosphere. Here the base of the lithosphere forms an upside-down drainage pattern for plume material away from the plume orifice toward the ridge axis. The flowline pattern forms by viscous fingering when there is insufficient plume material to form a continuous flow front. The hot plume material within the fingers cools by conduction and small-convection as it flows away from the plume. This process locally thins the lithosphere, channelizing the flow. It also cools the plume material, increasing its viscosity. The thickness and viscosity of the plume material self-organize to conserve material along the flow line and so that convection and conduction carry comparable amounts of heat flow into the overlying lithosphere. The flux of plume material (in m ³ s^-1 per meter along the flow front) scales to a critical quantity that is ~ Ra_crit κ S Δ T / T_η, where Ra_crit is the critical Rayleigh number for convection, κ is thermal diffusivity, S is the slope of the base of the lithosphere, Δ T is the excess temperature of the plume material, and T_η is the temperature to change viscosity by a factor of e. The plume material cools rapidly along the flowline until the heat flow into the lithosphere scales with the surface plate-age heat flow. The conditions for the formation of flowlines channels are not particularly restrictive, compatible with the common occurrence of flowline hotspots on the seafloor.
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 8162 Rheology: mantle (8033)
DE: 8415 Intra-plate processes (1033, 3615)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting