A "craton" is a part of the Earth's crust that's particularly old and stable. They're apparently often found at the heart of a continent or ocean. I don't know that I entirely understand it, but there's a Wikipedia article if you want more info.

That article also, btw, uses the term "felsic," a combination of "feldspar" and "silica." As in, "I felsic from eating too much feldspar and silica." That latter article also defines "acid rock" as being a volcanic rock with a high silica content; it's so straight-faced that I'm almost willing to believe that whoever wrote the article didn't know the term "acid rock" had any other meaning in other contexts.

Rock on, craton!