A possible mechanism for high-Mg andesite formation, including melting of subducting sediments and subsequent melt-mantle interaction, was examined by geochemical formulation of partial melting and melt-solid reactions. The modeling results demonstrate that a sediment-derived melt produced at 1050 °C and 1.0 GPa changes its composition from rhyolitic to andesitic as it dissolves olivine and clinopyroxene and crystallizes orthopyroxene. The resulting reaction product possesses major and incompatible trace element compositions close to high-Mg andesites in the Setouchi volcanic belt, southwest Japan.

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