Effects of active crustal movements on thermal structure in subduction zones

Abstract

SUMMARY In young suduction zones we observe steady uplift of island arcs. The steady uplift of island arcs is always accompanied by surface erosion. The long duration of uplift and erosion eVectively transports heat at depth to shallower parts by advection. If the rates of uplift and erosion are suYciently large, such a process of heat transportation will strongly aVect thermal structure in subduction zones. First, we quantitatively examine the eVects of uplift and erosion on thermal structure by using a simple 1-D heat conduction model, based on the assumption that the initial thermal state is in equilibrium. The results show that temperature increase, DT , due to uplift and erosion can be approximately evaluated by DT =n e tb at depth, where n e is the rate of uplift (erosion), t is the duration of uplift (erosion), and b is the gradient of the geotherm in the initial state. Next, considering the eVects of vertical crustal movements such as uplift and erosion in island arcs and subsidence and sedimentation in ocean trenches, in addition to the eVects of radioactive heat generation in the crust, frictional heating at plate boundaries and accretion of oceanic sediments to overriding continental plates, we numerically simulate the evolution process of the thermal structure in subduction zones. The result shows that the temperature beneath the island arc gradually increases as a result of uplift and erosion as plate subduction progresses. Near the ocean trench, on the other hand, the low-temperature region gradually expands as a result of sedimentation and accretion in addition to direct cooling by the cold descending slab. The surface heat flow expected from this model is low in fore-arc basins, high in island arcs and moderately high in back-arc regions.