There is only one file type that uses the .SC2ARCHIVE extension:
Blizzard StarCraft 2 Archive File
Data file used by StarCraft II, a sci-fi real-time strategy game; stores an archive of files in Blizzard's Mo'PaQ format (.MPQ files); may store models, textures, sounds, settings, and other game data; typically used for applying patches, such as bug fixes, to the game.
SC2ARCHIVE files are similar to .SC2DATA files, which are also stored in an MPQ format. Both file types can be opened with an MPQ editor.
Updated: February 20, 2010