Early Tertiary subduction zones and hot spots.

Geoid anomalies indicate that subducting slabs are major mass contributions; removing these effects, a simpler 'residual' geoid remains with highs strongly correlated with hot spot locations. Although neither the hot spots alone nor subducting slabs alone have maximum principal axes near the present pole, adding the contributions of the two gives a combined axis within a degree of the pole, suggesting that these two effects control the location of the spin axis. To establish whether changes in plate geometry could account for the observed polar motion, the locations of subduction zones are reconstructed in the hot spot framework for the early Tertiary, a time of significantly different plate motions. Suggests that changes in subduction geometry may cause a shift in the position of the rotation pole and, furthermore, that inertia tensor effects may be the link between plate velocities and the spin axis.-Author