HR: 0800h
AN: T41B-1203    [Abstracts]
TI: Estimating Upper Mantle Hydration from {\it In Situ} Electrical Conductivity
AU: * Behrens, J
EM: jbehrens@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0225 United States
AU: Constable, S
EM: sconstable@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0225 United States
AU: Heinson, G
EM: graham.heinson@adelaide.edu.au
AF: School of Earth and Environmental Sciences, The University of Adelaide, Adelaide, SA 5005 Australia
AU: Everett, M
EM: everett@geo.tamu.edu
AF: Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843 United States
AU: Weiss, C
EM: cjweiss@sandia.gov
AF: Sandia National Laboratories, PO Box 5800 MS-0750, Albuquerque, NM 87185 United States
AU: Key, K
EM: kkey@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0225 United States
AB: The electrical conductivity of 35-40 Ma Pacific plate has been measured {\it in situ}; one robust result is the presence of bulk anisotropy in the lithospheric upper mantle. We interpret this anisotropy to be a result of hydrothermal circulation into the upper mantle along spreading-ridge-parallel normal faults: the associated zones of serpentinized peridotite provide the pathways of enhanced electrical conductivity required by the data. Our modeling bounds the range of possible anisotropic ratios, which are then used to estimate the amount of water required to serpentinize the requisite amounts of peridotite. These data sets, however, do not indicate anisotropy in the bulk conductivity of the crust, nor in the asthenospheric mantle. This second point is significant, as recent measurements of sub-continental asthenospheric conductivity have been interpreted to indicate anisotropy aligned with present plate motion, with the diffusion of hydrogen through olivine advanced as an explanation.
DE: 3660 Metamorphic petrology
DE: 3914 Electrical properties
DE: 1025 Composition of the mantle
DE: 0600 ELECTROMAGNETICS
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting