These ecologies are not limited to MORs.
Convergent margins are areas where plates move together.
One plate subducts beneath the other, and numerous paths for fluid flow within the lithosphere are created. The next two overheads show a complete plate tectonic cycle of creation and destruction of oceanic lithosphere. During subduction, fluids which are expelled at the seafloor contain water, carbon dioxide, hydrogen sulfide and methane. Vent sites where these fluids exit the seafloor are characterized by chemosynthetic ecologies. Deep-sea chemosynthetic communities arise wherever there is a source of sulfide to be oxidized.