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A-subduction The movement of one continental lithospheric plate under another (subduction) in a collision zone, with the separation of part or all of the upper crust from the lower crust and mantle. The denser material subducts normally whilst the buoyant material can underthrust or overthrust the crust of the overriding plate. A-subduction, named after O. Ampferer, has also been called ‘delamination’, and is contrasted with B-subduction, named after Hugo Benioff, in which oceanic lithosphere subducts. A-subduction is postulated to involve shortening of a maximum of only a few hundred kilometres, whereas B-subduction can recycle thousands of kilometres of oceanic crust and upper mantle.