Quantitative modeling unifying magmatism and metamorphism

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Recent knowledge concerning the phase relationships of hydrous peridotitic and basaltic systems allows us to model fluid generation and migration in subduction zones. Such numerical model has been developed in this study. The results have been compared with geological and seismic observations. The comparisons suggest that the thermal structure (determined by age and subduction velocity) of the subducting plate strongly controls the distribution of the aqueous fluids and melts in subduction zones through the position of the dehydration reactions, and that water subducted into the mantle is expelled at shallower than 200 km in most of the subduction zones in the world.By constrast, as a consequence of the hot plate, including ridge subduction. pressure-temperature field appropriate for both high-and low-P/T regional metamorphism, together with a large amount of granitic magmatism, are produced simultaneously in the trench-foreacr system. The result supports the concept of paired metamorphic belts.Deformation and P-T conditions of the Cretaceous Ryoke-Sambagawa metamorphic belts have been analyzed based on recent numerical modeling of plastic flow at convergent plate boundaries. The analyzes suggest that a three-dimensional corner flow in the forearc wedge associated with moderate obliquity (more than 45 degrees for the angle between the subduction direction and the trench) can explain the observed prolate strain. Based on the analyzes, the contemporaneous Ryoke (low *P/T*) - Sambagawa (high-*P/T*) metamorphic belts are suggested to have been formed within a single trehch-forearc system by a series of the events, not by accidental amalgamation of two distinct terranes, supporting the concept of a 'paried metamorphic belts'. The constrasting low- and high-*P/T* metamorphic conditions are demonstrated to be simultaneously achieved in the forearc region with the dynamic flow associated with ridge subduction, where a large temperature gradient is produced.