Analyses of methane+water fluid inclusions from syntectonic quartz veins in melange boundins of the Kodiak accretionary complex, Alaska, indicate fluid temperatures ranging from 215¿ to 290¿C at depths between 10 and 14 km. These fluid temperatures are significantly higher than those predicted by conductive heat flow models of subduction zones. Given the available geological constraints, this discrepancy is interpreted as the result of migration of warm fluids from deeper structural levels along active fault zones during subduction-related underthrusting of these units. This interpretation requires more careful consideration of how migrating fluids affect the general thermal structure of subduction zones.