accretionary wedge

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accretionary wedge (accretionary prism) A tectonically thickened wedge of sediment found on the landward side of some trenches. The accretionary wedge consists of oceanic sediment scraped off the subducting plate (see SUBDUCTION), plus sediment derived from landward and deposited in the trench. Slices of sediment are added to the wedge by underthrusting and the trench migrates seaward, the continuation of this process producing an inversion.