EVOLUTION OF SLAB AND WEDGE THERMAL STRUCTURE IN TIME-DEPENDENT DYNAMIC MODELS OF SUBDUCTION

The thermal structure of subducting lithosphere, the mantle wedge and overriding plate determine the dehydration and melting processes occurring in subduction zones. This thermal structure is known to depend strongly on the slab age, slab dip and convergence velocity. Most models of subduction zone thermal structure are designed to examine the present thermal structure of particular subduction zones. Therefore, these kinematic models of subduction only consider the steady-state thermal structure. Here, we present the time evolution of the thermal structure of the slab crustal layer, mantle wedge and overriding plate from 2-D fully-dynamic models of subduction. Because the models are fully dynamic, the subduction velocity, slab dip and slab age vary in response to the evolving force balance as the slab sinks into the lower mantle. The slabs in these models undergo episodes of folding and buckling and long-term changes in trench motion from trench advance to trench retreat. We present results comparing the time-dependent evolution of the thermal structure with slab dip, convergence velocity, and trench motion. Specifically, we analyse how quickly changes in subduction parameters lead to changes in the expected regions of dehydration in the slab, melting of the slab surface and melting in the mantle wedge. To first order, we find the same dependence of thermal structure on subduction parameters as found in previous kinematic models. However, here we also provide constraints on the time-scale for perturbations to the thermal structure to propagate through the subduction system. We find that the thermal structure of the slab surface can be quite variable (+/- 500^oC), with short duration (< 5 my) episodes of heating due to changes in flow in the mantle wedge caused by changes in slab dip and the rate of advection of hot material into the mantle wedge. The thermal structure of the lithosphere overlying the mantle wedge mirrors these changes in the slab surface structure, but with smaller temperature variations due to the thicker thermal boundary layer.