On the high heat flow in the Nankai Trough area-a simulation study on a heat rebound process

A concentration of high heat flow (as high as 120-160 mW/m²) has been observed in the Nankai Trough, off southwest Japan, where the Philippine Sea plate (Shikoku Basin) is subducting beneath the Japanese landmass. We interpret this high heat flow in the subduction zone as being caused by the recovery of conductive heat flow to the theoretically expected value for the young Shikoku Basin lithosphere after cessation of hydrothermal heat exchange through sediment. The thickening sedimentary cover suppresses the rapid heat exchange between basement and sea water, whereas the topmost part of the basement allows a hydrothermal circulation within it to pump up heat from the hot plate to the sediment cover. We propose to call this process "heat rebound". Numerical simulation shows that significant heat flow recovery can occur and is largely influenced by the sedimentation rate. We believe that the high heat flow in the Nankai Trough is one of the heat rebound cases. However, rapid sedimentation in the trough also indicates that heat flow recovery expected by the simulation is not large enough to explain the trough high heat flow by the heat rebound process only.