Additional computational and laboratory experiments are investigating the dynamical evolution of the upper mantle in subduction zones. This work also looks at the role of subduction dynamics, specifically, a range in subduction parameters such as plate rate, plate age, rheology, etc., on the thermal and chemical evolution of the subducted lithosphere and the mantle wedge (lying between the slab and the surface).

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Here are a series of numerical experiments showing the thermal evolution of a subduction zone (temperature fields shown on left) for a different subduction rates and plate ages. Compositional fields (shown on right) clearly show the shape of the subducting slab.

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Defining the subducting lithosphere chemically enables us to accurately track slab surface temperatures for these various subduction parameters. This next figure shows plots of slab surface temperature at different depths for slow vs. old and thick vs thin plates. The horizons I, II, III and IV highlight conditions where melting of the sediment pile atop the slab should begin melting. Optimal conditions for melting the slab occur early-on after subduction initiation in the case of slow, young slabs (such as the Cascades) .

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The last figure shows the difference in slab morphology when different modes of subduction forces are applied. In the first frame, the slab is pushed from above (ridge push) and underplating occurs. The alternative is shown in the last frame where the slab sinks only due to its own buoyancy (e.g., it is cold and heavy). In this case the slab sinks back on itself, dip angles increase, the wedge corner flow is most vigorous and slab-wedge temperatures are maximum. The intermediate frame is a case of mixed "ridge push" and "slab pull".

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This work is part of a collaborative , multidisciplinary effort between Selwyn Sacks (Carnegie Institution of Washington; seismology), Julie Morris (Washington University; geochemistry), Marc Spiegelman (Lamont Doherty Earth Observatory; melt transport dynamics) and John Holloway (Arizona State University; high pressure-temperature petrology).