M. Gurnis et al., Tonga slab deformation: The influence of a lower mantle upwelling on a slab in a young subduction zone, GEOPHYS R L, 27(16), 2000, pp. 2373-2376
There are fundamental geographic variations in the deformation of slabs in
the transition zone. The seismic energy release and morphology of the Tonga
slab show that it is deforming faster and has accumulated more deformation
than any other slab. We show that Tonga overlies the edge of the large-sca
le Pacific superplume. There is no substantial aseismic penetration into th
e lower mantle beneath Tonga, consistent with initiation of subduction duri
ng the Eocene. Other major subduction systems overlay seismically fast stru
ctures. For long-lived subduction systems, the lower mantle tends to pull d
own on slabs while in Tonga the lower mantle pushes upward, partially accou
nting for the intense deformation. The perturbation to the state of slab st
ress due to large-scale mantle flow is 10 to 40 MPa - nearly as large as th
at expected from slab pull.