The influence of a mantle plume head on the dynamics of a retreating subduction zone

Abstract

The geological record and seismic tomography together contain multiple examples of mantle plumes and subducting oceanic slabs interacting, however consequences of these interactions and a mechanism for plumes to pass from the subducting to the overriding plate are uncertain. We present three-dimensional numerical simulations of a retreating subduction zone encountering a mantle plume head. We assess the impact a plume head has on the geometry of the trench and whether it can create a window within the subducted slab. In our models we consider slab/plume head interactions to be a natural consequence of plume head entrainment by plate motion combined with slab retreat. Strong slabs prevent plume heads from reaching the surface. For weak slabs, strongly buoyant plume heads cause local trench advance, slab windowing and accelerated slab retreat at the margins of the plume head. For large plume heads, this trench advance may contribute to crustal shortening in the overriding plate. Opening a slab window creates a potential conduit for transfer of plume material from the subducting plate to the overriding plate without terminating an active magmatic arc away from the point where the plume head tears the slab.