The dynamics of plume‐ridge interaction: 2. Off‐ridge plumes

Publisher Website
Google Scholar
Abstract
A variety of geophysical and geochemical evidence indicates that ascending mantle plumes can interact with ocean ridges located up to 1400 km away. I investigate the dynamics of this interaction using a simple model in which a point source with volume flux Q (analogous to a plume “stem”) releases buoyant fluid into a viscous corner flow driven by the divergence of rigid surface plates with thickness ∼(kx/U)1/2, where U is the half spreading rate. The point source is located at a distance xp from the ridge, and ridge migration is neglected. The buoyant fluid forms a thin sublithospheric layer whose thickness S(x, y) satisfies a nonlinear advection‐diffusion equation describing the balance of advection by the corner flow, buoyancy‐driven “self‐spreading,” flow toward the ridge along the sloping base of the lithosphere, and continuous accretion into the lithosphere. Numerical solutions of this equation yield scaling laws for the lateral extent W (“waist width”) of plume material along the ridge, the fraction R of the plume flux that crosses the ridge, and the maximum value of xp beyond which interaction ceases. The sloping base of the lithosphere has only a minor (few tens of percent) influence on these quantities, which are determined principally by the balance of advection and self‐spreading. An extension of the model to include plume‐induced lithospheric thinning shows that this process increases the waist width by an amount of order 10%. Finally, the model provides a new explanation for the observation that plumes interact primarily with ridges that are migrating away from them, rather than toward them.