In the world I'm building, there is a single continent. However, in the deeper parts of the ocean, there are hydrothermal vents. They're pretty necessary to my story, but I can't figure out why they would be there as to my knowledge they usually need to be near cracks in the tectonic plates.
I don't know if it's worth noting, but the core of my world is very small and there is little magma to be found. The hydrothermal vents are also about 16 500 ft down instead of around 16 000 feet.