Deflection of plumes by mantle shear flow: Experimental results and a simple theory

Linear hotspot tracks indicate relative motion between some hotspot sources and the overlying lithosphere. In order to better understand the effects of plate motions and mantle convection on mantle plumes and associated hotspots, we consider the path of a continuous plume of buoyant material in a shear flow. Laboratory experiments show that steady plumes bent over by a linear velocity profile follow parabolic trajectories. Plume trajectories are also shown to evolve quadratically in time toward a new steady shape after a change in the ambient flow. A remarkably simple description of plume dynamics provides good agreement with the experimental data: the plume trajectory is determined by the combination of horizontal advection by mantle flow and vertical rise according to a modified Stokes law. These results are applied to some idealised examples which demonstrate effects of depth-dependent mantle viscosity and return flow. At least some mantle plumes are likely to be sufficiently robust that they remain close to vertical and, therefore, stable. Key words: hotspots, mantle convection, plumes, shear flow INTRODUCTION Laboratory experiments with weak plumes in a shear flow Plumes of hot, buoyant and geochemically distinct materia