Dynamics of flowline Hotspots
Abstract
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 upsidedown 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 smallconvection 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 selforganize 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 s1 per meter along the flow front) scales to a critical quantity that is ~ Racrit κ S ∆ T / Tη, where Racrit is the critical Rayleigh number for convection, κ is thermal diffusivity, S is the slope of the base of the lithosphere, ∆ T is the excess temperature of the plume material, and Tη 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 plateage 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.
 Publication:

AGU Fall Meeting Abstracts
 Pub Date:
 December 2007
 Bibcode:
 2007AGUFM.V41G..06S
 Keywords:

 8121 Dynamics: convection currents;
 and mantle plumes;
 8137 Hotspots;
 large igneous provinces;
 and flood basalt volcanism;
 8162 Rheology: mantle (8033);
 8415 Intraplate processes (1033;
 3615)