Tectonic processes associated with subduction of oceanic crust, but unrelated to the collision of thick crustal masses or microplates, are presumed by many geologists to significantly affect the formation and deformation of large sedimentary bodies at underthrust ocean margins. More geologists are familiar with the concept of subduction accretion, which describes the tectonic attachment of rock and sediment masses to the margin's bedrock framework, than with other noncollision processes—for example, sediment subduction, subduction erosion, and subduction kneading. These are equally important processes controlling the geologic evolution of underthrust margins, and any one of them may predominate at a given place.
In our opinion, no single subduction-related tectonic process is the dominant or typical one that forges the geologic framework of modern underthrust ocean margins. It is likely, therefore, that the rock records of ancient underthrust margins are preserved in a multitude of structural and stratigraphic forms.