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Geophysical and geological observations document that beneath the submerged forearc, processes of sediment subduction and subduction erosion move large volumes of material toward the mantle. The conveying system is the subduction channel separating the upper plate from the underthrusting ocean plate. Globally, the zero-porosity or solid-volume rate at which continental debris is shuttled toward the mantle is estimated to be ∼2.5 km3/yr. To deliver this volume, the average thickness of the subduction channel is ∼1.0 km. Some deeply subducted material is returned to the surface of Earth as a component of arc magma or as tracks of high-P/T crustal underplates. But over long periods of time (>50 m.y.), most of the removed material is evidently recycled to the mantle.

Applying Cenozoic recycling rates to the past astonishingly implies that since 2.5 Ga a volume of continental crust equal to the standing inventory of ∼6 × 109 km3 has been removed from the surface of Earth. This minimum estimate does not include crustal material recycled at continental collision zones nor reliable estimates of recycling where large accretionary bodies form.

The volume of demolished crust is so large that recycling must have been a major factor determining the areal pattern and age distribution of continental crust. The small areal exposure of Archean rock is thus probably more a consequence of long-term crustal survival than the volume originally produced. Reconstruction of older supercontinents is made difficult if not unachievable by the progressive truncation of continental edges effected by subduction zone recycling, in particular by subduction erosion.

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