Our model highlights the importance of the subduction angle on the tectonic mode and volcanism. The reason for the sensitivity is that for steep (Mariana type) subduction mantle return flow maintains a hot wedge, whereas for flatter subduction (Tohoku type) the mantle return flow is sufficiently cooled by the slab and through the overlying crust that it stiffens and eventually becomes static. The stress environment becomes increasingly compressive as the wedge stiffens and the mechanical coupling length between the slab and the overlying plate lengthens. This enhanced compressive stress accelerates mountain building, which in turn causes faster erosion. The sedimentation due to this erosion is one of our principal observables.
As water is continuously released from the slab into the increasingly static overlying mantle, this region hydrates and eventually saturates. Further water release causes overpressured zones. The condition can be observed in the cores by two effects: the strong mechanical coupling length is reduced, resulting in reduced sedimentation, and the water, previously absorbed in the overlying wedge, is transferred to the volcanic front, causing increased volcanism. Note that mature Tohoku-type subduction geometry is the only type that should cause a voluminous volcanic front such as that observed in the Quaternary. It will not occur with the transitional or earlier geometry, as is also observed.
We have shown that this model is consistent with many different types of data and that it provides a framework so that it can be tested by other data in the future.