Britannica Sources used in this answer

How did subduction and terrane accretion help form the Cordilleran mountain belt of North America?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

continental landform Davis's proposed landscape-development states. The morphology shown is not actually time-indicative. For example, A could be a gully system in soft sediment or a canyon such as the Royal Gorge in Colorado, which is millions of years old. The ridge-ravine topography of B would normally develop under humid conditions, but the river meandering on alluvium indicates a prior or extraneous non-humid aggrading mechanism. The riverine plain of C implies a complex history of planation and aggradation in a current fluvial mode.

The formation of the North American Cordilleran mountain belt was driven by complex tectonic processes along the continent's western margin, primarily involving subduction and terrane accretion.

Beginning approximately 180 million years ago, as North America drifted westward over the Pacific Ocean floor, oceanic lithosphere was subducted beneath the continental margin. This process created a volcanic arc inland and a trench offshore, similar to the modern-day Andes.12

Simultaneously, the subducting oceanic plate carried various crustal fragments—such as island arcs, seamounts, and microcontinents—that were too buoyant to be subducted. As these fragments reached the subduction zone, they were "scraped off" and sutured onto the leading edge of the continent. These displaced crustal fragments, known as allochthonous terranes, were accreted to the western margin, significantly expanding the continent and causing intense deformation, folding, and faulting of the crust. This combination of subduction-related volcanism and the progressive collision of these terranes built the diverse ranges that constitute the modern Cordillera.234