Electrical conductivity structure beneath the Ryukyu trench-arc system and its relation to the subduction of the Philippine Sea plate

Abstract

Seafloor measurements of geomagnetic variations were undertaken at six sites in the Ryukyu trench-arc system in order to investigate the electrical conductivity structure of the crust and upper mantle with special reference to the subduction of the Philippine Sea plate. We attempted a two-dimensional modeling for a profile orthogonal to the strike of the Ryukyu trench-arc system, yielding a model showing two columnar conductors in the mantle wedge; one at the depth range from 20 to 60 km in the forearc region and the other at the depth range from 60 to 130 km or more beneath the northwestern margin of the Okinawa Trough behind the arc. The columnar conductor found below the forearc region is likely to be a zone containing water released through dehydration of some minerals in the hydrated peridotite, whereas the columnar conductor beneath the northwestern margin of the Okinawa Trough seems to correspond to a zone of partial melting which may be triggered by water released through dehydration of some other minerals. -from Authors