HR: 17:30h
AN: T54B-07    [Abstracts]
TI: The Role of Viscous Dissipation on the Thermal Structure of Subduction Zones
AU: * Lee, C
EM: cylee@vt.edu
AU: King, S D
EM: sdk@vt.edu
AB: The thermal structure of subduction zones is related to mechanisms of magma generation and surface heat flow. For active arc volcanism and high heat flow in the back arc, the presence of high temperature magma (> 1200 °C) and mantle wedge are essential. To explain the thermal structure, frictional heating, exothermic metamorphism, and radiogenic heat production have been suggested but, they are insufficient to increase the temperature of the mantle wedge. Experiments using compressible fluid approximations show significant heat generation in the regions of downwelling (subduction) from viscous dissipation; however, most subduction experiments use incompressible fluid approximations (e.g. Boussinesq Approximation, BA hereafter) so that the effects of viscous dissipation on the thermal structure can not be assessed. In this study, we quantitatively evaluate the effects of viscous dissipation on the thermal structure of subduction zones using a compressible fluid approximation (Truncated Anelastic Liquid Approximation, TALA hereafter). We use a 50 km-depth overriding plate over the mantle wedge and a kinematically driven subducting slab with the dip of 45 degrees, the age of 130 Ma and the subduction velocity of 5 cm/year. We use the rheology of dry and wet olivine for the viscous mantle wedge by assuming that the mantle wedge is wet down to 200 km. At the corner of the mantle wedge, low viscosity of serpentinite and partial coupling between the subducting slab and the mantle wedge are assumed down to 70 km and 120 km, respectively. We vary the mantle rheology by considering diffusion creep, combined creep of diffusion and dislocation, and constant viscosity. Uniform radiogenic heat production of 3×10^{- 10} J/kg·s is assumed in the upper 20 km of the lithosphere. For comparison, we conduct the corresponding experiments using BA with the same parameters. Slight increases in temperature of the mantle wedge and the subducting slab as well as increases in surface heat flow are observed in the experiments using the rheology of diffusion creep and constant viscosity. However, there are significant differences between the thermal structures in the experiments using the rheology of the combined creep of diffusion and dislocation. The TALA experiments develop high temperature cornerflow but the BA experiments do not. The BA experiments produce low heat flow values in the arc. This suggests that viscous dissipation plays an important role in the thermal structure of subduction zones because dislocation creep is thought to be a major flow mechanism in the upper mantle. Like previous studies, we do not observe high heat flow in the back arc and thus require further study.
DE: 0545 Modeling (4255)
DE: 8121 Dynamics: convection currents, and mantle plumes
SC: Tectonophysics [T]
MN: 2007 Fall Meeting