Open AccessLow‐velocity oceanic crust at the top of the Philippine Sea and Pacific plates beneath the Kanto region, central Japan, imaged by seismic tomography
Author(s) -
Matsubara Makoto,
Hayashi Hiroki,
Obara Kazushige,
Kasahara Keiji
Publication year - 2005
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2005jb003673
Subject(s) - geology , oceanic crust , crust , peridotite , seismology , pacific plate , subduction , convergent boundary , mantle wedge , mantle (geology) , geophysics , tectonics
We construct fine‐scale three‐dimensional P and S wave velocity structures beneath the Kanto region, central Japan, by seismic tomography with a spatial correlation of velocities. The Philippine Sea and Pacific plates subduct beneath the Eurasian plate in this area and are imaged with high velocities. Oceanic crust at the uppermost part of these subducting plates is a low‐velocity layer. Low‐velocity oceanic crust of the Philippine Sea plate subducts to a depth of approximately 80 km. There are also two low‐velocity bodies with relatively high V P / V S ratios of 1.80–1.90 in the mantle wedge above the oceanic crust of the Philippine Sea plate. We speculate that the westernmost of these two low‐velocity bodies consists of 20% partially serpentinized peridotite, continuous with gabbro in the oceanic crust of the uppermost Philippine Sea plate, while the eastern body is composed of 30% partially serpentinized peridotite. We trace the subducting oceanic crust of the Pacific plate to a depth of ∼120 km. The estimated V P / V S ratio of this layer is 1.85–1.90, which indicates a low probability of molten rock; the gabbroic oceanic crust may have been metamorphosed to garnet‐granulite.