Electrical Anisotropy Below Slow- and Fast-Moving Plates: Paleoflow in the Upper Mantle?

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Science  15 Feb 2002:
Vol. 295, Issue 5558, pp. 1270-1272
DOI: 10.1126/science.1066161

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Upper mantle electrical conductivities can be explained by hydrogen diffusivity in hydrous olivine. Diffusivity enhances the conductivity of olivine anisotropically, making the a axis the most conductive of the three axes. Therefore, the hypothesis that plate motion induces lattice-preferred orientation of olivine can be tested with the use of long-period electromagnetic array measurements. Here, we compared electrical anisotropies below the slow-moving Fennoscandian and fast-moving Australian plates. The degree of olivine alignment is greater in the mantle below the Fennoscandian plate than below the Australian plate. This finding may indicate that convection rather than plate motion is the dominant deformation mechanism.

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