Britannica Sources used in this answer

How can subducting oceanic crust contribute to volcanic arcs?

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

Earth's lithosphere and upper mantle — oceanic crust A cross section of Earth's outer layers, from the crust through the lower mantle.

Subducting oceanic crust contributes to the formation of volcanic arcs primarily through the release of volatile components, such as water and carbon dioxide, which are carried into the mantle by the descending slab.12

When the subducting plate reaches a depth of approximately 100 km (60 miles), the increasing heat drives off these volatiles. These compounds act as fluxes, lowering the melting temperature of the overlying mantle wedge. This process stimulates partial melting of the mantle, generating magma that rises through the overriding plate to form a line of volcanoes.123

The resulting volcanic arc is typically situated a few hundred kilometers behind the oceanic trench. If the overriding plate is oceanic, the volcanoes form an island arc, whereas if the overriding plate is continental, the volcanoes form inland, often resulting in more silica-rich compositions due to the interaction with the thicker continental crust.12