HR: 0830h
AN: T41C-0238    [PDF]
TI: Laboratory experiments on the interaction between on-axis plumes and segmented ridges
AU: * Minder, J
EM: justinminder@hotmail.com
AF: Vassar College, Box 735, Poughkeepsie, NY 12604 United States
AU: Viso, R F
EM: rviso@gso.uri.edu
AF: Graduate School of Oceanography/University of Rhode Island, Box 200 South Ferry Road, Narragansett, RI 02882 United States
AU: Kincaid, C R
EM: kincaid@gso.uri.edu
AF: Graduate School of Oceanography/University of Rhode Island, Box 200 South Ferry Road, Narragansett, RI 02882 United States
AB: Observational and modeling studies suggest that plume dispersal in the upper mantle is strongly influenced by plate driven mantle flow associated with spreading ridges and the presence of a sloping rheological boundary layer (RBL) at the base of the lithosphere. Questions remain as to how (or if) transform offsets in mid ocean ridges effect the dispersion of plume material. We examine the essential physical aspects of the case of a thermal plume rising beneath a segmented ridge system in a series of three-dimensional laboratory experiments. The working fluid is a glucose solution, with a temperature dependent viscosity. Divergent plate driven flow is modeled using Mylar sheets that are coupled to, and pulled in opposite directions across, the fluid surface. Buoyantly driven flow is produced using a circular resistance heater located at the base of the fluid. We consider cases when the plume rises beneath the center of a ridge segment and when the heater is located beneath a ridge-transform corner. The effect of a sloping RBL is modeled by cooling the fluid surface using dry ice. For the cases with plumes beneath segment centers, results show that long term patterns in along-axis plume dispersion are governed by the initial flattening and spreading of the plume head at the ridge. Plume heads produce a pocket in the RBL, which is subsequently filled by flow through the plume tail. Results show that transport of plume material in the vicinity of a ridge-transform offset is distinct from that which arises in the case of a ridge without any offset. This is due both to differences in RBL morphology and the pattern of plate driven upwelling associated with the presence of a transform boundary. The transform offset deflects the rising plume and, for cases of slow spreading rates and relatively weak plumes, blocks the flow of plume material to the distant ridge axis.
DE: 8120 Dynamics of lithosphere and mantle--general
SC: Tectonophysics [T]
MN: 2003 Fall Meeting