Evolution of starting mantle plumes: A comparison between numerical and laboratory models

Laboratory experiments on the initiation and development of mantle plumes suggest the formation of a bulbous plume head that grows in time by entrainment of surrounding material, followed by a thin feeder conduit. This type of plume is generally not seen in numerical models of mantle convection. To better determine the possible differences between numerical and laboratory experiments, we have numerically reproduced a published laboratory experiment on plume initiation. Theoretical predictions for the growth of the plume head have been verified and the experiments allowed for a new determination of a similarity constant. Models with a constant viscosity fluid show much less entrainment. Simulations using a plume rising from a thermal boundary layer with an olivine-type temperature-dependence show that most of the source material is contained in the plume head and that the conduit is largely composed of entrained material. Simulations with a more realistic non-Newtonian rheology show that plumes can rise much faster through the mantle, which will lead to higher temperatures of the plume head at the Earth's surface compared to what experiments with Newtonian rheology suggest.