Electrical Structure in Marine Tectonic Settings |
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| Authors: | Kiyoshi Baba |
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| Institution: | (1) Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka Kanagawa, 237-0061, Japan;(2) Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan |
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| Abstract: | This review paper presents recent research on electrical conductivity structure in various marine tectonic settings. In at
least three areas, marine electromagnetic studies for structural exploration have increasingly progressed: (1) data accumulations,
(2) technical advances both for hardware and software, and (3) interpretations based on multidisciplinary approaches. The
mid-ocean ridge system is the best-studied tectonic setting. Recent works have revealed evidence of conductive zones of hydrothermal
circulation and axial magma chambers in the crust and partial melt zones of the mid-ocean ridge basalt source in the mantle.
The role of water or dissolved hydrogen and its redistribution at mid-ocean ridges is emphasized for the conductivity pattern
of the oceanic lithosphere and asthenosphere. Regions of mantle upwelling (hotspot or plume) and downwelling (subducting slab)
are attracting attention. Evidence of heterogeneity exists not only in the crust and the upper mantle, but also in the mantle
transition zone. Electrical conductive zones frequently overlap seismic low-velocity zones, but discrepancies are also apparent.
Some studies have compared conductivity models with the results of seismic and other studies to investigate the physical properties
or processes. A new laboratory-based conductivity model for matured oceanic lithosphere and asthenosphere is proposed. It
takes account of both the water distribution in the mantle as well as the thermal structure. It explains observed conductivity
patterns in the depth range of 60–200 km. |
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| Keywords: | controlled-source electromagnetics electrical conductivity magnetotellurics marine tectonic settings |
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