The plates can consist of ocean crust or continental crust , or more often, a combination of the two. Places where plates meet are called plate boundaries or plate margins. Convergent boundaries are places where plates come together. Divergent boundaries are places where plates pull apart. Magma rises up from the mantle and adds new sea floor to the separating plates.
Fractures develop as the plates are pulled apart.
The superheated water is forced back up to the sea floor carrying dissolved minerals leached from the basalt ocean plate. A vent forms when the jet of water shoots through the sea floor and its dissolved minerals begin to precipitate out. The color depends on the minerals present in the water. Growth continues as long as there is a supply of hydrothermal fluid. Vents have been located at depths varying from 1500 to 4000 meters.