Abstract
Recent studies on seismic velocity and anisotropy structures beneath the northeastern Japan arc and their quantitative analyses have deepened our understanding of fluid circulation and magmatism in the mantle wedge. A prominent inclined low-velocity zone is clearly imaged in the mantle wedge sub-parallel to the down-dip direction of the Pacific slab, which is considered to be an upwelling flow induced by subduction of the slab. The flow direction is inferred to be parallel to the maximum-dip direction of the slab from shear-wave splitting analyses. Quantitative analyses of the inclined low-velocity and high-attenuation zone in the mantle wedge reveal that temperatures in the upwelling flow are higher than the wet solidus of peridotite and melts with a volume fraction of 1-4% are generated in the flow. These observations suggest that the upwelling in the mantle wedge plays an important role in arc magmatism.
