CONGESTED SUBDUCTION ZONES: THE RECORD OF COLLISIONS IN THE CONVERGENT MARGIN HISTORY

The collision between the Ogasawara Plateau and the Izu-Bonin-Mariana subduction zone is associated with a minor cusp in the surface trace of the plate boundary. In an attempt to understand this observation, Mason et al, 2010, developed 3D dynamic models of the collision between a buoyant plateau and an oceanic subduction zone.

We found that buoyant material ingested by the subduction zone produces a relative advance of the local region of the trench (either reduced rollback or absolute advance) naturally leading to the characteristic indentation of the plate boundary by the plateau. Depending on the strength and buoyancy of the plateau relative to the oceanic lithosphere, it may be subducted or it may be accreted with the associated formation of a slab window. Extending this model to ocean-continent convergent zones (Moresi et al, 2014), we show how the indentation of

buoyant exotic material also dominates terrane accretion.

When large blocks of material congest a subduction zone, the subduction zone needs to undergo signficiant re-arrangement for convergence to continue. We have modelled this process and observe characteristic patterns in the deformation of the over-riding plate, in the timing of the escape of material from behind the indenter, and in the oroclinal geometry that remains once the collision has completed.

References

Mason, W. G., Moresi, L., Betts, P. G., & Miller, M. S. (2010). Three-dimensional numerical models of the influence of a buoyant oceanic plateau on subduction zones. Tectonophysics, 483(1-2), 71–79. doi:10.1016/j.tecto.2009.08.021

Moresi, L., Betts, P. G., Miller, M. S., & Cayley, R. A. (2014). Dynamics of continental accretion. Nature. doi:10.1038/nature13033