Abstract:
We examine the thermal effects of seamount subduction. Seamount subduction may cause transient
changes in oceanic crust hydrogeology and plate boundary fault position. Prior to subduction, seamounts
provide high-permeability pathways between the basaltic crustal aquifer and overlying ocean that can focus
fluid flow and efficiently cool the oceanic crust. As the seamount is subducted, the high-permeability pathway
is closed, shutting down the advective transfer of heat. If significant fluid flow occurs, it would be restricted
after seamount subduction and would result in a redistribution of heat warming the trench and cooling landward
parts of the system. Additionally, subducting seamounts can influence the position of the plate boundary
fault that has thermal consequences by locally controlling the proportions of incoming sediment that
subduct and accrete. Shifting the décollement to the seafloor at the trench in the wake of seamount subduction
causes limited cooling focused at the toe of the margin wedge. We apply these features of seamount subduction
to a thermal model for the Nankai Trough Seismogenic Zone Experiment transect on the margin of
Japan. Models with hydrothermal circulation provide an explanation for anomalously high surface heat
flux observations near the trench. They yield temperatures of ~100°C−295°C for the rupture area of the
1944 Tonankai earthquake. Temperatures in the region of episodic tremor and slip are estimated at ~ 290°
C–325°C, ~ 70°C cooler than a model with no fluid circulation.
