Multiple-scale hydrothermal circulation in 135 Ma oceanic crust of the Japan Trench outer rise: Numerical models constrained with heat flow observations

Abstract

Anomalous high heat flow is observed within 150 km seaward of the trench axis at the Japan Trench offshore of Sanriku, where the old Pacific Plate (135 Ma) is subducting. Individual heat flow values range between 42 and 114 mW m -2, with an average of 70 mW m -2. These values are higher than those expected from the seafloor age based on thermal models of the oceanic plate, i.e., 50 mW m -2. The heat flow exhibits spatial variations at multiple scales: regional high average heat flow (100 km) and smaller-scale heat flow peaks (1 km). We found that hydrothermal mining of heat from depth due to gradual thickening of an aquifer in the oceanic crust toward the trench axis can yield elevated heat flow of the spatial scale of 100 km. Topographic effects combined with hydrothermal circulation may account for the observed smaller-scale heat flow variations. Hydrothermal circulation in high-permeability faults may result in heat flow peaks of a subkilometer spatial scale. Volcanic intrusions are unlikely to be a major source of heat flow variations at any scale because of limited occurrence of young volcanoes in the study area. Hydrothermal heat transport may work at various scales on outer rises of other subduction zones as well, since fractures and faults have been well developed due to bending of the incoming plate.