Oceanic crust sinks into the mantle at subduction zones. These are areas where two tectonic plates collide, and the denser oceanic plate is forced beneath the less dense continental plate.

Here's a more detailed explanation:

* Tectonic Plates: Earth's surface is divided into large, moving plates called tectonic plates. These plates constantly shift and interact with each other.

* Subduction: At subduction zones, one plate (usually the denser oceanic plate) slides beneath the other (continental or another oceanic plate).

* Downward Movement: As the oceanic plate descends, it gets pulled deeper into the Earth's mantle. This process is called subduction.

* Melting and Magma: The descending oceanic plate is subjected to intense heat and pressure. This causes the rocks to melt, forming magma.

* Volcanism: The magma rises to the surface, often erupting as volcanoes along the edge of the subducting plate.

Examples of Subduction Zones:

* The Ring of Fire: A zone of intense volcanic and seismic activity that circles the Pacific Ocean. It includes many subduction zones where the Pacific Plate is sinking beneath other plates.

* The Andes Mountains: Formed by the subduction of the Nazca Plate beneath the South American Plate.

* The Japanese Islands: A chain of volcanic islands formed by the subduction of the Pacific Plate beneath the Eurasian Plate.

Let me know if you have any other questions!