HR: 0830h
AN: OS41C-0819    [PDF]
TI: Thermal Constraints on Upper Basement Permeability Near a Venting Seamount
AU: * Hutnak, M
EM: mhutnak@es.ucsc.edu
AF: University of California, Santa Cruz, Earth Sciences Department 1156 High St., Santa Cruz, CA 95064 United States
AU: Fisher, A T
EM: afisher@es.ucsc.edu
AF: University of California, Santa Cruz, Earth Sciences Department 1156 High St., Santa Cruz, CA 95064 United States
AU: Zuehlsdorff, L
EM: lzuehls@mtu.uni-bremen.de
AF: University of Bremen, Department of Geosciences P.O. Box 33 04 40, Bremen, 28334 Germany
AU: Spiess, V
EM: vspiess@uni-bremen.de
AF: University of Bremen, Department of Geosciences P.O. Box 33 04 40, Bremen, 28334 Germany
AB: We used transient numerical simulations of coupled heat and fluid transport to quantify relations between fluid fluxes, basement permeability, and the vigor of local convection on seafloor heat flow patterns adjacent to a basement outcrop through which warm hydrothermal fluids are discharged. These finite-element models are designed to replicate conditions near the Baby Bare outcrop on 3.5-Ma seafloor on the eastern flank of the Juan de Fuca Ridge, where 5-20 L/s of warm fluid seeps from the seafloor. Several transects of heat flow observations co-located along seismic reflection profiles around this feature provide observational constraints for the models. Heat flow is not greatly influenced by venting at the outcrop at distances of several kilometers from the point of sediment onlap, but values rise abruptly immediately adjacent to the outcrop. The model domain consisted of a 21 km x 5 km radial grid, with 8 sedimentary and 6 basalt units, and a characteristic node spacing of 20-500 meters. Conductive simulations include a small rise in heat flow near the outcrop as a result of conductive refraction, but the magnitude of the rise is much smaller than observed. Additional simulations were run using elevated basement thermal conductivity as a proxy for local convection, to evaluate the vigor of local convection required to generate large increases in heat flow near the outcrop. Nusselt numbers (the ratio of heat transported within the edifice by conduction and advection to that which would be transported by conduction alone) of 100 $<$ Nu $<$ 1000 are required in order to homogenize temperatures along the sediment-basement interface and closely match the observed heat flow profile. Interestingly, it is not necessary to vent any fluid at the outcrop to generate this pattern; local convection is sufficient. Fully-coupled simulations were run with fluid forced from the seamount at 5-20 L/s. We find that local convection occurs within the seamount in cases with sufficiently low fluid velocities ($<$10 L/s) and high basement permeabilities ($>$10$^{-10}$m$^{2}$), and this convection is as effective at redistributing heat as single-pass flow in which little or no local convection occurs.
DE: 3015 Heat flow (benthic) and hydrothermal processes
DE: 8135 Hydrothermal systems (8424)
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting