Conduit diameter and buoyant rising speed of mantle plumes: Implications for the motion of hot spots and shape of plume conduits

[1] Mantle plumes are expected to be affected by large-scale flow in the Earth's mantle related to plate motions, subducted slabs, and possibly large-scale upwellings. Motion of plume conduits will depend on both large-scale flow and buoyant rising speed of the conduit through the mantle. Here we present a model of depth-dependent plume conduit temperature, viscosity, radius, and buoyant rising speed and use it to compute plume and hot spot motion. Results support a temperature anomaly of about 500 K at the plume base. In this case, sublithospheric temperature anomaly is about 150 K for the Iceland plume; transition zone anomaly is between 150 and 200 K for Iceland, about 250 K for Samoa, and about 300 K for Hawaii. Thermal plume radii are about 100 km in the upper mantle, increasing to about 200 km in the lower mantle. Beneath the lithosphere, viscosity in the vicinity of plumes is substantially reduced compared to the underlying mantle, and fast-moving plates deflect plumes by 200 km or less, corresponding to a plume conduit buoyant rise time of about 3 Myr between 400 and 100 km depth, where most of the shear flow due to plate motions occurs. During 100 Myr, plume conduits rise buoyantly from about 1500 - 2000 km depth. In many cases, computed hot spot motion agrees with previous computations: south-southeastward motion of the Hawaiian hot spot during the past 100 Myr, Louisville hot spot motion in a similar direction but at slower speed during the past 50 Myr, and westward motion of the Easter hot spot relative to Hawaii and Louisville. However, the previously computed substantial southward motion of the Kerguelen hot spot is not confirmed. If plume sources in the lowermost mantle are assumed to move with large-scale flow, they are predicted to be displaced toward the two large-scale upwellings beneath Africa and the Pacific relative to hot spot surface locations. For fixed sources, predicted tilts of the lower part of conduits tend to be opposite to that.