Plume-ridge interactions: ridgeward versus plate-drag plume flow

The analysis of mid-ocean ridges and hotspots that are sourced bydeep-rooted mantle plumes allows us to get a glimpse of mantle structure anddynamics. Dynamical interaction between ridge and plume processes have beenwidely proposed and studied, particularly in terms of ridgeward plume flow.However, the effects of plate drag on plume-lithosphere and plume-ridgeinteraction remain poorly understood. In particular, the mechanisms thatcontrol plume flow towards vs. away from the ridge have not yet beensystematically studied. Here, we use 2D thermomechanical numerical models ofplume-ridge interaction to systematically explore the effects of (i) ridge-spreading rate, (ii) initial plume head radius and (iii) plume-ridgedistance. Our numerical experiments suggest two different geodynamicregimes: (1) plume flow towards the ridge is favored by strong buoyantmantle plumes, slow spreading rates and small plume-ridge distances; (2) plume drag away from the ridge is in turn promoted by fast ridge spreadingfor small-to-intermediate plumes and large plume-ridge distances. We findthat the pressure gradient between the buoyant plume and spreading ridge atfirst drives ridgeward flow, but eventually the competition between platedrag and the gravitational force of plume flow along the base of the slopinglithosphere controls the fate of plume (spreading towards vs. away from theridge). Our results highlight that fast-spreading ridges exert strong plate-dragging force, which sheds new light on natural observations of largelyabsent plume-lithosphere interaction along fast-spreading ridges, such asthe East Pacific Rise.