Corrected entry: Black smoker hydrothermal vents are generally found in areas where the sea floor is spreading, opening fissures. Would not be found in subduction zones as in the Marianas Trench where crust is being destroyed.
Charles Austin Miller
23rd Aug 2018
Correction: The Marianas Trench Marine National Monument (protecting over 95,000 square miles of marine ecosystems) was established in 2009 after some 20 hydrothermal vents and associated exotic marine habitats were discovered in this subduction zone. Even more hydrothermal vents have been discovered in the Marianas Trench since then. The fact is, deep-sea hydrothermal vents (such as "black smokers" and "white smokers") can be found anywhere there is volcanic activity, including subduction zones. In fact, footage has been captured of black smoker hydrothermal vents in the Marianas Trench as recently as 2017. http://earth-chronicles.com/science/new-footage-from-the-mariana-trench-black-smokers.html.
Charles Austin Miller