HR: 16:00h
AN: S52J-01    [PDF]
TI: Mantle plumes as cause of long-lasting cratonic uplift implications for southern Africa
AU: * Sleep, N H
EM: norm@pangea.stanford.edu
AF: Department of Geophysics, Stanford University, Stanford, CA 94305 United States
AU: Nyblade, A A
EM: andy@geosc.psu.edu
AF: Department of Geosciences, Penn State University, University Park, PA 16802 United States
AB: Active mantle plumes are the prime suspects for midplate uplifts, like the Hawaiian swell. The question arises as to whether the effects of more ancient plumes can cause long-lasting uplifts like the swell in Southern Africa. Starting plume heads are unlikely to do this. First, the plume material flows laterally and ponds beneath regions of thin lithosphere. Only tens of kilometers of plume material remain beneath the cratonal keels. Second the ponded plume material suppresses secondary convection by having a stable boundary at its base. Heat continues to flow out of the top of the lithosphere. The net imbalance of heat flow in a column of material leads to subsidence. Even after the plume material has all cooled to the mantle adiabat, secondary convection supplies less heat flow to the lithosphere than is lost upward by conduction. The craton returns to its original thermal structure on a time scale of less than 200 m.y. In contrast, plume tails can linger for a long time beneath cratons and eventually raise the conductive geotherm into equilibrium with plume material. A lingering plume tail at ca. 80-90 Ma is a viable mechanism for the Southern African swell.
DE: 8110 Continental tectonics--general (0905)
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 9305 Africa
SC: Seismology [S]
MN: 2003 Fall Meeting