Mantle flow in subduction systems and its effects on surface tectonics and magmatism

Mantle flow triggered by subduction has a crucial role in the evolution of surface tectonics and volcanism. In this Review, we explore how patterns of mantle flow, particularly those in the upper mantle, evolve in response to subduction dynamics and cause surface topographic expressions. Poloidal flow in front of the slab (often called corner flow) is the main way new asthenospheric mantle is bought upwards into the mantle wedge. Toroidal flow around slab edges causes lateral mantle to flow from behind or adjacent to the slab edge towards the mantle wedge, for instance, at the Calabrian subduction zone under Etna. If accompanied by upwelling, toroidal flow can reach shallow depths and be traced in the geochemistry of volcanic rocks at the surface. Differential rates of trench retreat, the formation of slab windows and tears, and the switch from flat subduction to a steep dip angle can all cause increased asthenospheric input into the wedge, leading to distinct volcanism and topographic expressions at the surface. However, linking specific contributions of mantle flow to observed changes in dynamic topography is often difficult to distinguish from other crustal and lithospheric scale processes. To help distinguish the diverse expressions of mantle flow, future research should continue to iteratively update numerical and analogue models of mantle flow with emerging geological, geochemical and geophysical observations. Sinking slabs at subduction zones generate complex patterns of mantle flow that affect global mantle convection, surface deformation and volcanism. This Review explores how dynamic subduction-generated mantle flow evolves and causes surface topographic and volcanic expressions.