Geophys. J. Int., 132, 412-434, 1998.
Advection of plumes in mantle flow; implications on hotspot motion,
mantle viscosity and plume distribution
Bernhard Steinberger and R.J. O'Connell
SUMMARY
Because of their slow relative motion, hot spots, mainly in the Pacific,
are often used as a reference frame for defining plate motions.
A coherent motion of all Pacific hot spots
relative to the deep mantle may however bias the hot spot reference frame.
Numerical results on the advection of plumes, which are thought to
cause the hot spots on the Earth's surface, in a large-scale mantle
flow field are therefore presented. Bringing the results into agreement with
observations also leads to conclusions regarding the viscosity structure
of the Earth's mantle as well as the sources and distribution of plumes.
The abrupt change in direction
of the Hawaiian-Emperor chain implies an upper mantle viscosity under the
Pacific of 1.5 times 10**20 Pas or less. Slow relative
motion of hotspots requires high lower mantle viscosity,
unless hotspots are located at large-scale stationary upwellings
that are currently unresolved by seismic tomography. For our preferred
model, we obtain coherent motion of Pacific hotspots in a reference frame
of no net rotation as well as coherent motion relative to African hotspots,
caused by return flow antiparallel to plate
motion. Advection and regional differences in life expectancy
can to a large part explain the distribution of plumes in relation
to ridges, subduction zones (present and past) and seismic anomalies.
Plume conduits are substantially tilted
in the lower mantle. The surface motion of hotspots is often
smaller than the advection rate of plume conduits in the lowermost mantle.