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[SCG63-05] Paleostress profile across the Sanbagawa metamorphic belt along the Asemi River, Central Shikoku, Japan, estimated from dynamically recrystallized grain size of quartz
Keywords:grain size piezometer, subduction zone, paleostress profile
The new data lie well on the interpolated curve of the previous grain size data in the high-grade side of the chlorite zone. The gradually decreasing grain size profile go across metamorphic isograds. This suggests that the grain sizes reflect the deformation associated with the metamorphism. In the low-grade side of the chlorite zone, the new data lie around the previously-obtained value. In the high-grade side of the chlorite zone, quartz grains show fabrics with c-axis parallel to the foliation and perpendicular to the lineation. The quartz deformation structures indicate subgrain rotation recrystallization and grain boundary migration toward subgrain boundaries in neighboring quartz grains. In the low-grade side of the chlorite zone, quartz fabrics are rather random, but quartz grains still show subgrain boundaries and grain boundary migration toward subgrain boundaries in neighboring grains, suggesting dynamic recrystallization. These quartz deformation structures are common throughout in quartz schist in the analyzed samples. This indicates that all the obtained quartz grain sizes are the product of dynamic recrystallization. By applying grain size piezometers, it is suggested that there are a stress peak at the high-grade side of the chlorite zone and a stress decrease toward the low-grade side in the chlorite zone.