Electrical conductivities of pyrolitic mantle and MORB materials up to the lowermost mantle conditions |
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| Authors: | Kenji Ohta Kei Hirose Masahiro Ichiki Katsuya Shimizu Nagayoshi Sata Yasuo Ohishi |
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| Affiliation: | 1. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8551, Japan;2. Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan;3. Center for Quantum Science and Technology under Extreme Conditions, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan;4. Japan Synchrotron Radiation Research Institute, 1-1-1 Koto, Sayo, Hyogo 679-5198, Japan;1. Earth-Life Science Institute, Tokyo Institute of Technology, Meguro, Tokyo 150-8550, Japan;2. Department of Earth and Planetary Science, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan;1. Laboratory for High Temperature and High Pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou 550002, China;2. Department of Geology and Geophysics, Yale University, New Haven, CT 06511, USA;1. School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom;2. Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, United Kingdom;3. School of Electrical Engineering and Computer Science, Department of Geology and Geophysics, and Center for Computation and Technology, Louisiana State University, Baton Rouge, LA 70803, United States;1. Key Laboratory for High-Temperature and High-Pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;2. Institute for Planetary Materials, Okayama University, Misasa, Tottori 682-0193, Japan;3. Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100, USA;4. State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;1. Geodynamics Research Center, Ehime University, Ehime 790-8577, Japan;2. Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8550, Japan;3. Japan Synchrotron Radiation Research Institute, Hyogo 679-5198, Japan |
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| Abstract: | The electrical conductivities of natural pyrolitic mantle and MORB materials were measured at high pressure and temperature covering the entire lower mantle conditions up to 133 GPa and 2650 K. In contrast to the previous laboratory-based models, our data demonstrate that the conductivity of pyrolite does not increase monotonically but varies dramatically with depth in the lower mantle; it drops due to high-spin to low-spin transition of iron in both perovskite and ferropericlase in the mid-lower mantle and increases sharply across the perovskite to post-perovskite phase transition at the D″ layer. We also found that the MORB exhibits much higher conductivity than pyrolite. The depth–conductivity profile measured for pyrolite does not match the geomagnetic field data below about 1500-km depth, possibly suggesting the existence of large quantities of subducted MORB crust in the deep lower mantle. The observations of geomagnetic jerks suggest that the electrical conductivity may be laterally heterogeneous in the lowermost mantle with high anomaly underneath Africa and the Pacific, the same regions as large low shear-wave velocity provinces. Such conductivity and shear-wave speed anomalies are also possibly caused by the deep subduction and accumulation of dense MORB crust above the core–mantle boundary. |
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