HR: 16:45h
AN: T44C-04    [Abstracts]
TI: Enormous Power Output and Fluid Fluxes Driven Through a few Mid-plate Outcrops
AU: Fisher, A T
EM: afisher@pmc.ucsc.edu
AF: University of California, Santa Cruz, Department of Earth Sciences, Santa Cruz, CA 95064, United States
AU: * Hutnak, M
EM: mhutnak@usgs.gov
AF: U.S Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, United States
AU: Harris, R N
EM: rharris@coas.oregonstate.edu
AF: Oregon State University, College of Ocean and Atmospheric Sciences, Corvallis, OR 97331, United States
AU: Stein, C
EM: cstein@uic.edu
AF: University of Illinois at Chicago, Department of Earth and Envifonmental Sciences, Chicago, IL 60607, United States
AU: Wang, K
EM: Kelin.Wang@nrcan-rncan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Center PO Box 6000, Sydney, BC V8L 4B2, Canada
AU: Spinelli, G
EM: spinelli@nmt.edu
AF: New Mexico Tech., Department of Earch and Environmental Science, Socorro, NM 87801,
AU: Pfender, M
EM: pfender@uni-bremen.de
AF: University of Bremen, Geowissenschaften Klagenfurter Strasse, Bremen, D-28359, Germany
AU: Villinger, H
EM: vill@zfn.uni-bremen.de
AF: University of Bremen, Geowissenschaften Klagenfurter Strasse, Bremen, D-28359, Germany
AU: Silver, E
EM: esilver@pmc.ucsc.edu
AF: University of California, Santa Cruz, Department of Earth Sciences, Santa Cruz, CA 95064, United States
AB: Hydrothermal circulation on ridge flanks, areas far from the magmatic influence of plate creation, is responsible for roughly 30% of the heat loss from oceanic lithosphere and a fluid mass flux on the order of 10¹⁵ kg/yr. The thermal state of subducting oceanic lithosphere influences melting conditions in the overlying mantle wedge, the extent of sediment dewatering associated with mineralogical and rheological transitions, and the nature of tectonic and seismic processes at depth. Understanding the distribution and processes associated with ridge flank hydrothermal circulation has been limited by a lack of detailed co-located bathymetric, seismic reflection, and thermal data. We have collected and analyzed such a composite data set on a portion the Cocos Plate approaching the subduction zone along the Middle America Trench, offshore of the Nicoya Peninsula, Costa Rica. This survey covers a seafloor area of 14,500 km² where crustal ages vary between 18 and 24 Ma. Low- permeability sediments in the study area are thick (400-500 m) and continuous, except where seamounts and other highly-permeable basalt outcrops penetrate the seafloor. Observational data show that enormous quantities of heat and fluid flow from the crust into the ocean through small areas of basement exposure. The seafloor conductive heat flux in most of this area is 10-30% of predicted lithospheric values, requiring an integrated advective power output of 800-1,400 MW. Upper basement temperatures in this area are 5–40 ^oC, requiring a fluid mass flux of 0.1–3 x 10¹² kg/yr to sustain the advective power output. The ten basement outcrops mapped in this region comprise <2% of the seafloor area, and only a few of these features show evidence for fluid outflow. Modeling studies suggest that discharge is favored from smaller outcrops, consistent with our observations. Even if the advective power output were distributed evenly across all ten basement outcrops in this area, each outcrop would discharge as much heat as a high-temperature vent field. Observations of such large fluid fluxes emanating from ridge-flank outcrops indicate the importance of these features to lithospheric fluid and heat budgets, elucidate crustal physical properties and forces required to sustain enormous fluxes, and provide constraints on the thermal state of the upper oceanic lithosphere prior to subduction.
DE: 3015 Heat flow (benthic)
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 3021 Marine hydrogeology
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting