Editing Abyssal plain (section)

==Formation==
{{See also|Plate tectonics|Mantle convection}}
[[File:Tectonic plate boundaries.png|thumb|[[Oceanic crust]] is formed at a [[mid-ocean ridge]], while the [[lithosphere]] is [[subducted]] back into the [[asthenosphere]] at [[oceanic trench]]es]]
[[File:Earth seafloor crust age 1996 - 2.png|thumb|Age of oceanic crust (red is youngest, and blue is oldest)]]

Oceanic crust, which forms the [[bedrock]] of abyssal plains, is continuously being created at mid-ocean ridges (a type of [[divergent boundary]]) by a process known as [[Igneous rock#Decompression|decompression melting]].<ref name=Wilson1993>{{Cite book|isbn=978-0-412-53310-5|author=Marjorie Wilson|year=1993|publisher=Chapman & Hall|location=London|title=Igneous petrogenesis|author-link=Marjorie Wilson}}</ref> [[mantle plume|Plume]]-related decompression melting of solid mantle is responsible for creating ocean islands like the [[Hawaiian islands]], as well as the ocean crust at mid-ocean ridges. This phenomenon is also the most common explanation for [[flood basalt]]s and [[oceanic plateau]]s (two types of [[large igneous province]]s). Decompression melting occurs when the upper [[Mantle (geology)|mantle]] is [[partial melting|partially melted]] into [[magma]] as it moves upwards under mid-ocean ridges.<ref name=White2001>{{Cite journal
|author1=R.S. WHITE |author2=T.A. MINSHULL |author3=M.J. BICKLE |author4=C.J. ROBINSON |title=Melt Generation at Very Slow-Spreading Oceanic Ridges: Constraints from Geochemical and Geophysical Data
|journal=Journal of Petrology
|volume=42
|issue=6
|pages=1171–1196
|year=2001
|doi=10.1093/petrology/42.6.1171
|bibcode=2001JPet...42.1171W|doi-access=free
}}</ref><ref name=Wilson>{{Cite book
|title=Understanding the Earth
|author1=Geoff C. Brown |author2=C. J. Hawkesworth |author3=R. C. L. Wilson |page=93
|url=https://books.google.com/books?id=Kgk4AAAAIAAJ&pg=PA93
|isbn=978-0-521-42740-1
|edition=2nd
|year=1992
|publisher=Cambridge University Press}}</ref> This upwelling magma then cools and solidifies by [[Conduction (heat)|conduction]] and [[convection]] of heat to form new [[oceanic crust]]. [[Accretion (geology)|Accretion]] occurs as mantle is added to the growing edges of a [[Plate tectonics|tectonic plate]], usually associated with [[seafloor spreading]]. The age of oceanic crust is therefore a function of distance from the mid-ocean ridge.<ref>{{harvnb|Condie|1997|p=50.}}</ref> The youngest oceanic crust is at the mid-ocean ridges, and it becomes progressively older, cooler and denser as it migrates outwards from the mid-ocean ridges as part of the process called [[mantle convection]].<ref name="University of Winnipeg">Kobes, Randy and Kunstatter, Gabor.[http://theory.uwinnipeg.ca/mod_tech/node195.html Mantle Convection] {{Webarchive|url=https://web.archive.org/web/20110114151750/http://theory.uwinnipeg.ca/mod_tech/node195.html |date=14 January 2011 }}. Physics Department, University of Winnipeg. Retrieved 23 June 2010.</ref>

The [[lithosphere]], which rides atop the [[asthenosphere]], is divided into a number of tectonic plates that are continuously being created and consumed at their opposite [[Plate boundaries#Types of plate boundaries|plate boundaries]]. Oceanic crust and tectonic plates are formed and move apart at mid-ocean ridges. Abyssal hills are formed by stretching of the oceanic lithosphere.<ref name=Buck1998>{{Cite journal
|author1=W. Roger Buck |author2=Alexei N. B. Poliakov |title=Abyssal hills formed by stretching oceanic lithosphere
|journal=Nature
|volume=392
|pages=272–275
|date=19 March 1998
|doi=10.1038/32636
|issue=6673|bibcode = 1998Natur.392..272B |s2cid=4422877 }}</ref> Consumption or destruction of the oceanic lithosphere occurs at [[oceanic trenches]] (a type of [[convergent boundary]], also known as a destructive plate boundary) by a process known as [[subduction]]. Oceanic trenches are found at places where the oceanic lithospheric slabs of two different plates meet, and the denser (older) slab begins to descend back into the mantle.<ref>{{harvnb|Condie|1997|p=83.}}</ref> At the consumption edge of the plate (the oceanic trench), the oceanic lithosphere has thermally contracted to become quite dense, and it sinks under its own weight in the process of subduction.<ref name=Olson1>
{{Cite book
|title=Mantle convection in the earth and planets
|author1=Gerald Schubert |author2=Donald Lawson Turcotte |author3=Peter Olson |chapter-url=https://books.google.com/books?id=ij4BaFFpYHAC&pg=PA16
|page=16 ''ff''
|chapter=Chapter 2: Plate tectonics
|isbn=978-0-521-79836-5
|year=2001
|publisher=Cambridge University Press}}
</ref> The subduction process consumes older oceanic lithosphere, so oceanic crust is seldom more than 200 million years old.<ref name=DSDP>{{Cite web
|year=2010
|url=http://www.deepseadrilling.org/about.htm
|title=About the Deep Sea Drilling Project
|publisher=Deep Sea Drilling Project
|location=[[Texas A&M University]], [[College Station, Texas|College Station]], [[Texas]]
|access-date=24 June 2010}}</ref> The overall process of repeated cycles of creation and destruction of oceanic crust is known as the [[Supercontinent cycle]], first proposed by [[Canadians|Canadian]] [[geophysicist]] and [[geologist]] [[John Tuzo Wilson]].

New oceanic crust, closest to the mid-oceanic ridges, is mostly basalt at shallow levels and has a rugged [[topography]]. The roughness of this topography is a function of the rate at which the mid-ocean ridge is spreading (the spreading rate).<ref name=Small1992>{{Cite journal
|author1=Christopher Small |author2=David T. Sandwell |title=An analysis of ridge axis gravity roughness and spreading rate
|journal=Journal of Geophysical Research
|volume=97
|issue=B3
|pages=3235–3245
|date=10 March 1992
|url=http://topex.ucsd.edu/sandwell/publications/49.pdf
|access-date=23 June 2010
|doi=10.1029/91JB02465
|bibcode=1992JGR....97.3235S}}</ref> Magnitudes of spreading rates vary quite significantly. Typical values for fast-spreading ridges are greater than 100&nbsp;mm/yr, while slow-spreading ridges are typically less than 20&nbsp;mm/yr.<ref name=White2001/> Studies have shown that the slower the spreading rate, the rougher the new oceanic crust will be, and vice versa.<ref name=Small1992/> It is thought this phenomenon is due to [[Fault (geology)|faulting]] at the mid-ocean ridge when the new oceanic crust was formed.<ref name=Buck2005>{{Cite journal
|author1=W. Roger Buck |author2=Luc L. Lavier |author3=Alexei N.B. Poliakov |title=Modes of faulting at mid-ocean ridges
|journal=Nature
|volume=434
|pages=719–723
|date=7 April 2005
|doi=10.1038/nature03358
|pmid=15815620
|issue=7034
|bibcode = 2005Natur.434..719B |s2cid=4320966 |url=https://resolver.caltech.edu/CaltechAUTHORS:20150319-085050879 }}</ref> These faults pervading the oceanic crust, along with their bounding abyssal hills, are the most common tectonic and topographic features on the surface of the Earth.<ref name=Buck1998/><ref name=Buck2005/> The process of seafloor spreading helps to explain the concept of [[continental drift]] in the theory of plate tectonics.

The flat appearance of mature abyssal plains results from the blanketing of this originally uneven surface of oceanic crust by fine-grained sediments, mainly clay and silt. Much of this sediment is deposited from turbidity currents that have been channeled from the continental margins along submarine canyons down into deeper water. The remainder of the sediment comprises chiefly dust (clay particles) blown out to sea from land, and the remains of small [[Phytoplankton|marine plants]] and [[Zooplankton|animals]] which sink from the upper layer of the ocean, known as [[pelagic sediments]]. The total sediment deposition rate in remote areas is estimated at two to three centimeters per thousand years.<ref name=Kuenen1946>{{Cite journal
|author=Philip Henry Kuenen
|title=Rate and mass of deep-sea sedimentation
|journal=American Journal of Science
|volume=244
|pages=563–572
|date = August 1946
|doi=10.2475/ajs.244.8.563|issue=8|bibcode=1946AmJS..244..563K
|doi-access=free
}}</ref><ref name=DSDP1972>{{Cite book
|title=Initial Reports of the Deep Sea Drilling Project, Volume XII (covering Leg 12 of the cruises of the Drilling Vessel Glomar Challenger)
|volume=12 |editor=Laughton, A. S. |editor2=Berggren, W. A.
|author1=T.A. Davies |author2=A.S. Laughton |chapter=Chapter 11. Sedimentary Processes in the North Atlantic
|page=915
|chapter-url=http://www.deepseadrilling.org/12/volume/dsdp12_11.pdf
|issn=1936-7392
|year=1972
|publisher=U.S. Government Printing Office
|location=Washington, D.C.
|doi=10.2973/dsdp.proc.12.111.1972
|access-date=24 June 2010|display-editors=etal}}</ref> Sediment-covered abyssal plains are less common in the Pacific Ocean than in other major ocean basins because sediments from turbidity currents are trapped in oceanic trenches that border the Pacific Ocean.<ref name=Underwood1986>{{Cite journal
|author1=Michael B. Underwood |author2=Charles R. Norville |title=Deposition of sand in a trench-slope basin by unconfined turbidity currents
|journal=Marine Geology
|volume=71
|issue=3–4
|pages=383–392
|date = May 1986
|doi=10.1016/0025-3227(86)90080-0|bibcode=1986MGeol..71..383U}}</ref>

Abyssal plains are typically covered by deep sea, but during parts of the [[Messinian salinity crisis]] much of the [[Mediterranean Sea]]'s abyssal plain was exposed to air as an empty deep hot dry salt-floored sink.<ref name=Krijgsman1996>{{cite journal
|author=Krijgsman W|author2=Garcés M|author3=Langereis CG|author4=Daams R|author5=Van Dam J|title=A new chronology for the middle to late Miocene continental record in Spain
|journal=Earth and Planetary Science Letters
|volume=142
|issue=3–4
|pages=367–380
|year=1996
|doi=10.1016/0012-821X(96)00109-4
|bibcode=1996E&PSL.142..367K|url=http://doc.rero.ch/record/13400/files/PAL_E203.pdf |display-authors=etal}}</ref><ref name=Clauzon1996>{{cite journal
|vauthors=Clauzon G, Suc JP, Gautier F, Berger A, Loutre MF |title=Alternate interpretation of the Messinian salinity crisis: Controversy resolved?
|journal=Geology
|volume=24
|issue=4
|pages=363–6
|year=1996
|doi=10.1130/0091-7613(1996)024<0363:AIOTMS>2.3.CO;2
|bibcode = 1996Geo....24..363C }}</ref><ref name=Vandijk1998>{{cite journal
|vauthors=van Dijk JP, Barberis A, Cantarella G, Massa E |title=Central Mediterranean Messinian basin evolution. Tectono-eustasy or eustato-tectonics?
|journal=Annales Tectonicae
|volume=12
|issue=1–2
|pages=7–27
|year=1998}}</ref><ref>{{cite journal
|vauthors=Bachea F, Olivet JL, Gorini C, Rabineaua M, Baztan J |title=Messinian erosional and salinity crises: View from the Provence Basin (Gulf of Lions, Western Mediterranean)
|journal=Earth and Planetary Science Letters
|volume=286
|issue=1–2
|pages=139–57
|year=2009
|doi=10.1016/j.epsl.2009.06.021
|url=http://archimer.ifremer.fr/doc/2009/publication-6870.pdf
|access-date=1 October 2010
|bibcode=2009E&PSL.286..139B|s2cid=30843908
|display-authors=etal}}</ref>