Pressure-Temperature-Water Production Rate Paths of Boundary Metamorphic Rocks and Mechanical Coupling between Subduction Slab and Island Arc Crust

Abstract

Boundary metamorphic rocks as exemplified by Sanbagawa metamorphic rocks have chemical records accompanied by physical processes in garnet and amphiboles. Garnet showing chemical zoning from core to rim grew during prograde metamorphism, which is the process of boundary rock subduction, and the pressure-temperature-water production rate path can be precisely determined by the modified differential thermodynamic method with the volume fraction of garnet. The results of the paths can be discussed in a dynamic system involving mechanical coupling between slab and arc crust, thermal interaction, and dehydration reaction, suggesting that mechanical coupling is weakend by a dehydration reaction.