マントルウェッジ中の水の移動と沈み込み帯における火山フロントの形成 [in Japanese] Migration of Aqueous Fluid in the Mantle Wedge and Formation of the Volcanic Front in Subduction Zones [in Japanese]
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The H<SUB>2</SUB>O released from the descending oceanic lithosphere is thought to play an important role in subduction zone magmatism as this H<SUB>2</SUB>O might trigger partial melting of the mantle wedge. Previous models for the formation of subduction zone magmas have assumed that H<SUB>2</SUB>O flows easily due to percolation in the whole mantle wedge. However, if there is incomplete wetting of mantle mineral grain boundaries (that is, the dihedral angle at triple junctions between grains is more than 60°), fluid does not form an interconnected network. In such a case, H<SUB>2</SUB>O might be trapped as an interstitial fluid in the peridotite and transported to deeper parts of the mantle wedge rather than triggering partial melting. In the present study, the geometrical distribution of aqueous fluid in textural equilibrium with polycrystalline olivine is investigated by measuring the dihedral angle at pressures of 3 and 5 GPa and at temperatures of 800 and 1000°C t for the purpose of clarifying the mobility of aqueous fluid in the upper mantle. By combining these data with previously published results, the extent of wetting within the mantle wedge as a function of pressure and temperature is obtained. It is suggested that the connectivity of aqueous fluid in hydrous upper mantle peridotite at convergent plate boundaries might control the position of the volcanic front in subduction zones.
- J. Geogr.
J. Geogr. 109(4), 590-599, 2000-08-25
Tokyo Geographical Society