Upper mantle conductivity structure of the back-arc region beneath northeastern China

The upper mantle electrical conductivity structure of the pacific back-arc beneath northeastern China was investigated through long-period magnetotell uric (TMT) and geomagnetic depth sounding (GDS) experiments. MT and GDS res ponses were obtained up to periods of 10(5) similar to 10(6) seconds, and w ere inverted to one-dimensional (1-D) models with minimum and smooth struct ure constraints, respectively. The resulting conductivity model was compare d with past models and the mantle transition zone beneath northeastern Chin a is more conductive than those of other tectonic settings by almost one or der of magnitude in the depth range of 400 similar to 600 km. This feature may correspond to the presence of a stagnant slab beneath this region. In t he mantle at a depth of less than 400 km, the conductivity profile has a si milar feature to that in the thermal and extensional tectonic region in the southwestern United States.