マントル・ウエッジの構造と島弧の火山活動

概要

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The origin of arc volcanism has not been clarified with a reasonable model of the physical and chemical processes. Seismological observations show that a hot mantle wedge is adjacent to the cool subducting slab. Observed volcanic material and heat flow are largely concentrated near the volcanic front and decrease to backarc. There is a systematic variation in the chemical composition of volcanic rocks across the arc. These observations do not seem to be well interpreted by the convection that is mechanically induced by the slab motion. The mantle diapirs containing magmas fail to have a sufficiently high ascending speed simultaneously with enough heat. Therefore another model with an ascending mantle flow beneath the volcanic front is proposed to explain the mechanism of magma generation as well as those observations. According to the model, the migration of mass in the ascending flow causes upwelling of hot material from deeper mantle, which supplies heat and buoyancy to preserve the flow itself. The subducting slab brings volatile and other components that facilitate partial melting in the ascending flow. The flow that has passed the top moves toward backarc, and it is gradually cooled so that magmas in it are partly solidified and have more incompatible elements.
特定非営利活動法人日本火山学会の論文
1986-04-30