The Thermal Effects of Plate‐Bending‐Related Thickening of the Oceanic Crustal Aquifer in the Nankai Trough and Japan Trench Subduction Zones

Abstract

AbstractFor the Nankai Trough and Japan Trench subduction zones, we examine the combined thermal effects of lateral heat exchange by fluid circulation in an oceanic crustal aquifer and the thickening of that aquifer due to plate‐bending‐related faulting. Faults induced by the bending of a plate entering a subduction zone are hypothesized to increase the depth over which vigorous hydrothermal circulation can redistribute heat in the oceanic crust. Previous 1‐D (vertical) thermal models have examined how aquifer thickening can mine heat from deep in the crust seaward of the trench. Here we construct 2‐D thermal models that include aquifer thickening and lateral heat exchange in the aquifer. We vary the maximum aquifer thickness and the landward extent to which hydrothermal circulation persists within the subducted crust. For the Nankai margin, models most consistent with heat flux data require vigorous fluid circulation extending up to 150 km landward of the trench; aquifer thickening is permitted but not required for models to be consistent with the heat flux observations. Conversely, for the Japan Trench, preferred models include substantial aquifer thickening (maximum aquifer thickness of 1.8–5 km); vigorous circulation extending landward of the trench is permitted but is not required. For hot subduction zones, the thermal effects of aquifer thickening are modest relative to the large lateral advective heat redistribution. For cold subduction zones, where small lateral temperature gradients limit the amount of lateral heat redistribution, aquifer thickening can be the dominant process generating thermal anomalies.