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

Answer 1

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

Answer 2

Ocean to continent divergent boundaries