Subduction adjacent to deep continental roots: Enhanced negative pressure in the mantle wedge, mountain building and continental motion

Subduction near to a deep continental root is modeled with finite elements. The root restricts asthenospheric corner flow, which increases mantle-wedge suction. The suction pulls the continental root toward the subduction zone, simultaneously promoting trenchward continental motion and compressive tectonics in the lithosphere between the root and the subduction zone. In a 2-D model with a root that extends to 250 km depth and lies 300 km from the mantle-wedge corner, we find two-fold increase in mantle-wedge suction and nearly a four-fold increase in continental compression (to 5 × 1012 N/m) compared to a rootless reference model. In 3-D modeling, we find that distance to the subduction zone is more important than root width (in subduction strike direction) or reasonable variations in sub-lithospheric viscosity structure, with the root-enhanced suction effects diminishing rapidly as the wedge corner-root distance increases beyond 400 km. When finite-width roots are wider than the distance to the mantle-wedge corner and closer than 400 km, compression of the continent between the root and the subduction zone is > 50% that found in the infinite-width root.