A synthesis of heat flow determinations and thermal modeling along the Nankai Trough, Japan

We review marine heat flow data along the Nankai Trough and show that observations >30 km seaward of the deformation front are 20% below conductive predictions (129-94 mW m(-2)) but consistent with the global heat flow average for oceanic crust of the same age (16-28 Ma). Heat flow values 30 km seaward of the deformation front are generally 20% higher than conductive predictions. This heat flow pattern is consistent with the advection of heat by fluid flow in the subducting oceanic crust and explains both the high heat flux in the vicinity of the trench, >200 and >140 mW m(-2), and steep landward declines to values of approximately 60 mW m(-2) over distances of 65 and 50 km along the Muroto and Kumano transects, respectively. Along the Ashizuri transect, the lack of heat flow data precludes a definitive interpretation. We conclude that fluid flow in the subducting oceanic crust leads to temperatures that are generally 25 degrees C higher near the toe of the margin wedge and 50-100 degrees C lower near the downdip limit of the seismogenic zone than estimated by purely conductive models.