Temperature and melt fraction distributions in a mantle wedge determined from the electrical conductivity structure: Application to one nonvolcanic and two volcanic regions in the Kyushu subduction zone, Japan

We propose a new method for estimating the temperatures and melt fractions of the upper mantle. Our method is based on connecting the electrical conductivity structure from geophysical observations with laboratory‐determined relationships between the electrical conductivity and temperature of four nominally anhydrous minerals (olivine, orthopyroxene, clinopyroxene, and garnet) and basaltic melt. The temperatures are expressed as the upper limit temperatures using the Hashin‐Shtrikman lower bound in solid phases and using the Hashin‐Shtrikman upper bound in solid‐liquid mixed phases. We apply the method to a nonvolcanic and two volcanic regions in the Kyushu subduction zone, southwest Japan. Our results suggest that the temperatures of the upper mantle are 1100–1450°C for dry mantle and 900–1350°C for wet mantle and that the melt fractions of the upper mantle are <20% beneath the two volcanic regions and <5% beneath the nonvolcanic region for both dry and wet mantle.