Large-scale rigid-body rotation in the mantle wedge and its implications for seismic tomography

Using a combined finite difference and marker-in-cell technique, we performed two-dimensional coupled petrological-thermomechanical numerical simulations of intraoceanic subduction. The simulations indicate that parts of the mantle wedge can become trapped between rheologically weak, hydrated, and partially molten upwellings (cold plumes) and the subducting slab. The structures form at various depths and develop circular, elliptic, or irregular shapes. The combined effect of the tractions caused by upwelling and subduction causes these regions to rotate. Our simulations investigate the parameters controlling the occurrence and long-term stability of such rigid, rotating structures. Circular rotating structures like ''subduction wheels'' are characteristic of models with relatively young (20-30 Myr) slabs and intermediate (2-5 cm/yr) subduction rates. We propose that the development of such circular features may explain some of the isolated seismic velocity anomalies in the mantle wedge.