Seismologists discover complex structure in Tonga mantle wedge

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Seismic imaging reveals layered structures in the mantle overlying the oceanic slab sinking in the Tonga subduction zone as shown in the two vertical cross-sections. The contoured surface of the Tonga slab is shown in gray with earthquake hypocenters ...
Seismic imaging reveals layered structures in the mantle overlying the oceanic slab sinking in the Tonga subduction zone, as shown in the two vertical cross-sections. The contoured surface of the Tonga slab is shown in gray, with earthquake hypocenters indicated in pink. Figure produced by Y. Zheng and T. Lay.

The subduction zones where oceanic plates sink beneath the continents produce volcanic arcs such as those that make up the "rim of fire" around the Pacific Ocean. The volcanoes are fed by molten rock rising within a wedge of the Earth's mantle above the subducting plate. Although geologists have a pretty good picture of the processes that produce volcanic arcs, a new study finds that the structure of the mantle wedge may be far more complex than anyone had imagined.


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