Editing Oceanic trench (section)

== Geographic distribution ==
[[File:Pacific elevation2.jpg|thumb|upright=1.4|Major Pacific trenches (1–10) and fracture zones (11–20): 
1. [[Kermadec Trench|Kermadec]]
2. [[Tonga Trench|Tonga]]
3. Bougainville
4. [[Mariana Trench|Mariana]]
5. [[Izu–Ogasawara Trench|Izu–Ogasawara]]
6. [[Japan Trench|Japan]]
7. [[Kuril–Kamchatka Trench|Kuril–Kamchatka]]
8. [[Aleutian Trench|Aleutian]]
9. [[Middle America Trench|Middle America]]
10. [[Peru–Chile Trench|Peru–Chile]]
11. Mendocino
12. Murray
13. Molokai
14. Clarion
15. Clipperton
16. Challenger
17. Eltanin
18. Udintsev
19. East Pacific Rise (S-shaped)
20. Nazca Ridge
]]

There are approximately {{convert|50000|km|mi|abbr=on}} of [[Convergent boundary|convergent plate margins]] worldwide. These are mostly located around the Pacific Ocean, but are also found in the eastern [[Indian Ocean]], with a few shorter convergent margin segments in other parts of the Indian Ocean, in the Atlantic Ocean, and in the Mediterranean.{{sfn|Stern|2005}} They are found on the oceanward side of [[island arcs]] and Andean-type [[orogen]]s.{{sfn|Kearey|Klepeis|Vine|2009|p=250}} Globally, there are over 50 major ocean trenches covering an area of 1.9 million km<sup>2</sup> or about 0.5% of the oceans.{{sfn|Harris|MacMillan-Lawler|Rupp|Baker |2014}}

Trenches are geomorphologically distinct from [[trough (geology)|troughs]]. Troughs are elongated depressions of the sea floor with steep sides and flat bottoms, while trenches are characterized by a V-shaped profile.{{sfn|Harris|MacMillan-Lawler|Rupp|Baker |2014}} Trenches that are partially infilled are sometimes described as troughs, for example the [[Makran]] Trough.{{sfn|Dastanpour|1996}} Some trenches are completely buried and lack bathymetric expression as in the [[Cascadia subduction zone]],{{sfn|Thomas|Burbidge|Cummins|2007}} which is completely filled with sediments.{{sfn|Goldfinger|Nelson|Morey|Johnson|2012}} Despite their appearance, in these instances the fundamental [[plate tectonics|plate-tectonic]] structure is still an oceanic trench. Some troughs look similar to oceanic trenches but possess other tectonic structures. One example is the [[Lesser Antilles]] Trough, which is the forearc basin of the [[Lesser Antilles subduction zone]].{{sfn|Westbrook|Mascle|Biju-Duval|1984}} Also not a trench is the [[New Caledonia]] trough, which is an extensional [[sedimentary basin]] related to the [[Tonga-Kermadec subduction zone]].{{sfn|Hackney|Sutherland|Collot|2012}} Additionally, the Cayman Trough, which is a [[pull-apart basin]] within a [[transform fault]] zone,{{sfn|Einsele|2000}} is not an oceanic trench.

Trenches, along with [[volcanic arc]]s and [[Wadati–Benioff zone]]s (zones of [[earthquake]]s under a volcanic arc) are diagnostic of convergent plate boundaries and their deeper manifestations, [[subduction zones]].{{sfn|Stern|2005}}{{sfn|Kearey|Klepeis|Vine|2009|p=250}}{{sfn|Geersen|Voelker|Behrmann|2018}} Here, two [[tectonic plates]] are drifting into each other at a rate of a few millimeters to over {{convert|10|cm|sigfig=1|sp=us}} per year. At least one of the plates is [[oceanic lithosphere]], which plunges under the other plate to be recycled in the [[Earth's mantle]].

Trenches are related to, but distinct from, continental collision zones, such as the [[Himalayas]]. Unlike in trenches, in continental collision zones [[continental crust]] enters a subduction zone. When buoyant continental crust enters a trench, subduction comes to a halt and the area becomes a zone of continental collision. Features analogous to trenches are associated with [[collision zone]]s. One such feature is the ''peripheral foreland basin'', a sediment-filled [[foredeep]]. Examples of peripheral foreland basins include the [[floodplains]] of the [[Ganges River]] and the [[Tigris-Euphrates river system]].{{sfn|Stern|2005}}