Pressure-driven processes explain the decreasing magnetization of the subducting oceanic crust in the Japan Trench

초록

Despite the decreases in temperature and permeability of oceanic plates with increasing age, hydrothermal circulation (HC) can be rejuvenated in the 130-Ma old Pacific plate in the vicinity of the Japan Trench, substantially affecting the thermal structure and remaining amount of magnetization (RAM). To decipher the roles of HC in the thermal structure and the RAM, the vigor and extent of HC in the vicinity of the Japan Trench should be quantitatively evaluated. Here we numerically show that HC is rejuvenated in the outer-rise zone but ceases after subduction owing to permeability evolution. The calculated thermal structure explains the measured heat flow evolution but negates the HC-driven thermal demagnetization, which was thought to decrease the RAM after subduction. Instead, we propose that the pressure-driven processes decrease the RAM after subduction through the demagnetizations of titanomaghemite and magnetite and the mineral phase transitions from maghemite to hematite. Increasing pressure reduces magnetization of the subducting plate below the Japan Trench through pressure-driven demagnetization and phase transition from maghemite to hematite, according to numerical modelling of coupled fluid and heat transport.

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