2.4 Andes Plate Margins: Island Arcs: Subduction of an Oceanic Plate beneath a Continental Plate

The subduction of oceanic lithosphere gives rise to two different types of mountain belts.
1). Where oceanic lithosphere subducts beneath an oceanic plate, an island arc and related tectonic features develop.
2). Subduction beneath a continental block, on the other hand, results in the formation of a volcanic arc along the margin of a continent. Plate boundaries that generate continental volcanic arcs are often referred to as Andean type plate margins.

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Island arcs represent what are perhaps the simplest mountain belts. These structures result from the steady subduction of oceanic lithosphere, which may last 100 million years or more.

Somewhat sporadic volcanic activity, the emplacement of plutonic bodies at depth, and the accumulation of sediment that is scraped from the subducting plate gradually increase the volume of crustal material capping the upper plate.

Some mature volcanic island arcs, such as Japan, appear to have been built upon a pre-existing fragment of continental crust.

The continued development of a mature volcanic island arc can result in the formation of mountainous topography consisting of belts of igneous and metamorphic rocks.

This activity, however, is viewed as just one phase in the development of a major mountain belt.

As you will see in later videos, some volcanic arcs are carried by a subducting plate to the margin of a large continental block, where they become involved in a major mountain building episode.