| Budget Amount *help |
¥12,300,000 (Direct Cost: ¥12,300,000)
Fiscal Year 2005: ¥4,300,000 (Direct Cost: ¥4,300,000)
Fiscal Year 2004: ¥4,500,000 (Direct Cost: ¥4,500,000)
Fiscal Year 2003: ¥3,500,000 (Direct Cost: ¥3,500,000)
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| Research Abstract |
This project aims at (1)constructing a numerical model for predicting 3-D deformation of metamorphic belts intercalated between the plates, as well as thermal structures, for variable driving forces from plate motions and deformations, (2)constructing a numerical model for predicting material cycling (in particular water) under perturbed situations associated with ridge subduction, which is thought to be critical for metamorphism and magmatism, (3)comparing the model results and the P-T and deformation history recorded in metamorphic and igneous rocks, in order to obtain a perspective view. According to (1) to (3), we obtain the following results : (A)Among the possible deformation fields (3-D collision, obduction, corner flow and/or squeezing flow in the forearc wedge, and combination of these flows), plain strain or oblate strain is dominant, whereas prolate strain, that is observed in the Cretaceous regional metamorphic belts of the Japan arcs (Ryoke and Sambagawa belts), Franciscan belt in the western United States, is reproduced only in the 3-D corner flow, (B)the Cretaceous regional metamorphic belts of the Japan arcs is deduced to have been produced by 3-D corner flow in the forearc wedge, associated with ridge subduction in Cretaceous, which had supplied both heat and water to the forearc wedge to heat up and soften the region, (C)considering the phase relationships of the hydrous basaltic and peridotitic rocks, the water cycling is thought to be limited to a shallow part (<50 km depth), without significantly carrying water to the deeper part, when the ridge subduction occurs, (D)the water cycling associated with subduction of plates with an average age is also limited to relatively shallow part (<200 km depth) due to dehydration of the major hydrous mineral phases, whereas nominally anhydrous minerals (such as olivine) bring a small amount of water to the deeper mantle.
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