It's exciting in a geeky way to learn that the deep-sea plateau called the Rio Grande Rise appears to contain granitic rocks. Dredging two years ago brought up samples, and this week the "video evidence" from a submersible dive to the Rise was cited as further proof. That doesn't seem like much evidence, and nothing has been published yet, and the video I've seen doesn't look at all granite-y, but I'll go with it. Granite is a big deal, because the Rio Grande Rise is supposed to be a hotspot track created by a "mantle plume," and mantle plumes are not supposed to create granites.
The Rio Grande Rise is a long welt of mostly volcanic rocks that extends from southern Brazil out to sea nearly all the way to the Mid-Atlantic Ridge at the island (and hotpot) of Tristan da Cunha. On the other side, a similar feature named Walvis Ridge extends to northern Namibia, in Africa. They aren't sexy places to study because they seem to be well explained for now. But lo and behold, a closer look has brought forth evidence of a noteworthy amount of granite out there in the South Atlantic.
What prompted this closer look? I surmise that it was money and shipboard time. Japan and Brazil arranged a joint mission, using Japan's Yokosuka research ship and its manned submersible Shinkai 6500, to survey the waters off Rio de Janeiro. On the way across the Atlantic the vessels took the opportunity to look at the Rio Grande Rise.
There are models for the Rio Grande Rise and Walvis Ridge that don't involve hotspots, explaining them instead as stretch marks in the South Atlantic crust made as the South America and Africa plates separated. Perhaps a chip of the South American continent got lost and sank with the ocean crust around it, like the Seychelles Islands in the Indian Ocean or Jan Mayen island in the North Atlantic. Maybe an amalgamated model that mixes mantle plumes and plate cracking will arise to explain the granite.
I would never have heard about this, except that the Brazilian-Japanese project decided to splash its news as the discovery of a "Brazilian Atlantis." If my understanding is correct, the media, as usual, have totally missed the point.