Summary: The Thermal State of the Upper Mantle;
No Role for Mantle Plumes
Don L. Anderson
California Institute of Technology
Seismological Laboratory 252-21
Pasadena, CA 91125 U.S.A.
A variety of geophysical data indicates that long wavelength temperature variations of the
asthenosphere depart from the mean by ± 200°C, not the ± 20°C adopted by plume theoreticians.
The `normal' variation, caused by plate tectonic processes, such as subduction cooling,
continental insulation and small-scale convection, encompasses the temperature excesses that
have been attributed to hot jets and thermal plumes. Geophysical estimates of the average
potential temperature of the upper mantle are about 1400°C. Asthenospheric convection at
ridges, rifts and fracture zones and at the onset of continental breakup is intrinsically 3D, giving
rise to shallow pseudo-plume-like structures without deep thermal instabilities. Deep narrow
thermal plumes are unnecessary and are precluded by uplift and subsidence data, and widespread