Plate Subduction and Arc Magmatism(＜Special Section＞The 60th Anniversary of VSJ “Latest Advances and Future Perspectives in Volcanology”)

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  • NAKAJIMA Junichi
    Department of Earth and Planetary Sciences, Graduate School of Science and Engineering, Tokyo Institute of Technology

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Other Title
  • プレートの沈み込みと島弧マグマ活動(＜特集＞日本火山学会60周年「火山学の最新動向と今後の展望」)
  • プレートの沈み込みと島弧マグマ活動
  • プレート ノ シズミ コミ ト トウコ マグマ カツドウ

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The subduction zone system on the Earth is over 40,000km long, comparable to the circumference of the Earth. The active processes -brittle deformation, metamorphism, convection and volcanism- beneath volcanic arcs or continental margins are all linked with fluids derived from subducting oceanic plates. Here I review recent geophysical observations in subduction zones and organize our thoughts on ongoing magmatic processes, focusing on a low-velocity, high-attenuation, and low-resistivity zone in the mantle wedge as an indicator of melt migration paths. In subduction zones where a plate at moderate to old age is subducting, two types of melt migration paths are observed, with an inclined migration path for a gently dipping slab and a sub-vertical migration path for a steeply dipping slab. These observations suggest that melt transportation is primarily governed by the geometry of a mantle upwelling flow developed sub-parallel to the down-dip direction of the slab. However, melts appear to migrate sub-vertically to volcanoes in young subduction zones. Release of slab-derived fluids at shallow depths would produce partial melting only in the fore-arc tip of a mantle upwelling flow, and hence melts may migrate sub-vertically by buoyancy, instead of effective transportations through the upwelling flow as observed in relatively old subduction zones. An understanding of subduction zone processes with reference to the more quantitative integration of all earth science categories (seismology, volcanology, geodesy, petrology, mineralogy, geochemistry, geology, geomorphology, etc.) will be required to improve our knowledge of arc magmatism.

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