what is an area where an oceanic plate goes down into the mantle?

Ocean to continent divergent boundaries

An area where an oceanic plate goes down into the mantle is known as a subduction zone. Subduction occurs when two tectonic plates converge, and one plate, usually the denser oceanic plate, is forced beneath the other one and sinks into the mantle. This process is responsible for the formation of features like deep-sea trenches, volcanic arcs, and earthquakes.

To find specific examples of subduction zones, you can refer to well-studied regions known for this tectonic activity. Some notable examples include the Pacific Ring of Fire, where several subduction zones encircle the Pacific Ocean. This includes the subduction of the Pacific Plate beneath the North American and South American Plates in the western coast of the Americas. Another well-known subduction zone is located in the western Pacific Ocean, where the Philippine Sea Plate subducts beneath the Eurasian Plate, creating volcanic activity in countries like Japan and the Philippines.

http://www.google.com/search?hl=en&lr=&as_qdr=all&q=tectonic+plates

Search through many of these until you find terminology.

Here's one example, although it doesn't give an exact name for this motion. But keep looking.
http://www.platetectonics.com/book/page_4.asp