Woods Hole Oceanographic Institution

Dr Rob. L. Evans

»Electrical Lithosphere Beneath the Kaapvaal Craton
»Gulf Of Mexico Gas Seep
»MELT MT Results
»MELT Area Off-Axis Structure
»Wrightsville Beach Geophysics and Hydrology
»Karst Formation off North Carolina
»Review of Shallow Offshore EM Work
»EPR MMR Experiment
»Towed EM System
»Offshore MT and Subduction Systems
»Shallow Porosity Structure on the Continental Shelf
»Oceanic and Continental Mantle Resistivity
»New Jersey EM Survey
»Eel River EM Survey
»Impact of groundwater on EM data
»Electrical structure of Slave Craton
»Report of Shoreline Change Workshop

Greg Hirth, Rob. L. Evans and Alan D. Chave, Comparison of continental and oceanic mantle electrical conductivity: Is the Archean lithosphere dry?, G3, Dec 8, 2000

Electrical conductivity profiles derived from magnetotelluric and geomagnetic sounding methods provide a means of constraining upper mantle properties that is complementary to seismic studies. We analyse conductivity profiles for an Archean craton and and oceanic setting, in conjunction with independent constraints on mantle geotherms, to estimate the water content of the upper mantle in these very different geologic environments. Results from this analysis indicate that the Archean lithosphere contains less water than the oceanic mantle in the depth range between ~150 and ~250 km. Below ~250 km these oceanic and continental environments show similar conductivities, suggesting that the water content of the mantle does not vary significantly between ~250 km and the 410-km discontinuity. These observations indicate that the Archean lithosphere may be stabilised against convective instabilities partly because it has a high viscosity associated with a dry composition.

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