Rob L. Evans, Alan D. Chave and John R. Booker, On the importance of offshore data for magnetotelluric studies
of ocean-continent subduction systems, Geophys. Res. Letts, vol 29, 2002
The presence of water in the mantle wedge overlying a
subduction zone is expected to significantly enhance electrical
conductivity, raising it above that of the cold subducting slab, or
surrounding regions of dehydrated mantle. This suggests that
magnetotelluric (MT) transects across subduction systems,
measuring regional electrical conductivity structure, might be
able to indirectly trace the pathways of water migration into the
mantle. For ocean-continent subduction, it is logistically simpler to
collect MT transects on the continental side of the system.
However, we show that such land data are relatively insensitive to
details of the electrical connections between the ocean and mantle.
In contrast, seafloor measurements on the landward and seaward
side of the trench are very sensitive to these electrical connections,
and are essential to understanding the electrical structure of the
entire subduction system. In particular, the conductivity structure of
the hydrated mantle wedge overlying the slab can only be studied
using offshore MT data.We demonstrate this result using a model of
an ocean-continent system, although our results can be generalised
to other subduction geometries.
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