MODEL STUDIES OF ADVECTIVE HEAT-FLOW ASSOCIATED WITH COMPACTION AND DEHYDRATION IN ACCRETIONARY PRISMS

Surface heat flow across the deformation front of subduction zones sho ws complex patterns, and fluid flow is often invoked to interpret thes e patterns. Here we estimate the maximum possible amount of fluid flow due to sediment compaction and dehydration in subduction zones, and c ompare these estimates with the required fluid flow to produce signifi cant thermal disturbances across faults and vents in two- and three-di mensions. The results show that lateral heat loss becomes significant for faults or vents with thickness or diameter less than about 1 km. F or two-dimensional channel flow in fault zones or permeable strata, su bduction-induced compaction alone can hardly provide enough steady sta te flow to cause surface heat flow anomalies such as that observed in the Barbados accretionary prism [Foucher et al., 1990; Langseth et al. , 1990]. Fluid flow in three-dimensional pipes (vents or vent fields) of a few hundred meters to approximately 1 km in diameter is efficient in producing thermal disturbances; but steady state flow in small iso lated pipes of a few meters in diameter is incapable of producing meas urable heat flow anomalies. Small-scale heat flow anomalies which are observed in some accretionary prisms are probably best explained by in termittent, transient flow.