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Published August 15, 2000 | Published
Journal Article Open

Tonga slab deformation: The influence of a lower mantle upwelling on a slab in a young subduction zone

Abstract

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-scale Pacific superplume. There is no substantial aseismic penetration into the lower mantle beneath Tonga, consistent with initiation of subduction during the Eocene. Other major subduction systems overlay seismically fast structures. For long-lived subduction systems, the lower mantle tends to pull down on slabs while in Tonga the lower mantle pushes upward, partially accounting for the intense deformation. The perturbation to the state of slab stress due to large-scale mantle flow is 10 to 40 MPa — nearly as large as that expected from slab pull.

Additional Information

© 2000 by the American Geophysical Union. This work has been supported by NSF grants EAR-9809771 and EAR-9814908. We thank C. Conrad and D. Müller for helpful comments on the manuscript. This represents Contribution Number 8695, Division of Geological and Planetary Sciences, California Institute of Technology.

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