HR: 16:15h
AN: V34B-02    [Abstracts]
TI: Laboratory Investigations of Plume Head Dispersion at a Segmented Spreading Ridge With a Sloping Rheological Boundary Layer
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
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: The dispersion of buoyant plume material in the upper mantle beneath a spreading ridge is examined using laboratory experiments. Specific goals of the experiments included determining the role of a cold rheological boundary layer (lithosphere/asthenosphere boundary) and the effects of a transform offset on along-axis flow of plume material. The rheological boundary layer (RBL) is established by cooling the surface of the fluid with dry ice. Plate driven flow is simulated by dragging mylar sheets in opposite directions across the surface of the fluid. The diverging plates force upwelling of deeper, ambient temperature fluid into the ridge axis, and a sloping RBL similar to lithospheric plates is created. A thermally buoyant plume is introduced into the plate driven flow, midway along a ridge axis segment. The plume signal is observed to spread along axis to a distance no greater than the diameter of the fully evolved plume head. Preferential along-axis channeling of the plume material is not observed. We suggest that thermal erosion of the RBL by the plume head creates an initially dome-shaped indentation in the base of the lithosphere. This pocket grows elongate in the axis-perpendicular directions through time with plate spreading. The volume of the growing pocket is maintained by the flux of plume material through the plume conduit. In cases with a plume located directly beneath a ridge-transform intersection, plume flow was deflected by the cold, highly viscous plane of the transform fault. The axis segment (near or far) to which the plume material is deflected may be spreading rate dependant. In all cases, the presence of a thermal RBL proved to be an important element in dispersion of relatively low viscosity plumes amidst a forced flow of higher viscosity ambient fluid.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 3035 Midocean ridge processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting