In the complex tectonic setting of central Japan, two oceanic plates overlap with each other as they sink into the mantle, resulting in fluid release, mantle melting and volcanism. A study published online this week in Nature Geoscience quantifies the relative contribution of each plate to the overall fluid budget and helps clarify the subsurface configuration of the plates.
Hitomi Nakamura and colleagues analysed young volcanic rocks from central Japan to determine the chemical signature of fluids released by the Philippine Sea and Pacific plates as they dip down. They found that the fluid contributed by each plate is chemically distinct and that even though the plates overlap, the Philippine Sea plate appears not to block fluid released from the underlying Pacific plate.
The data suggest that chemical signatures of plate-derived fluids can be used to understand the geometry of subducting plates and hence the seismicity such settings.