ImportMaster at 20:25, 8 April 2022

2022-04-08T20:25:22Z

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[[File:Ridge render.jpg|thumb|270px|right|Spreading at a mid-ocean ridge]]
[[File:Tectonic plate boundaries.png|thumb|right|250px|Diagram of oceanic ridge]]
[[File:World Distribution of Mid-Oceanic Ridges.gif|right|250px|thumb|World Distribution of Mid-Oceanic Ridges: the big picture.]]
[[File:Earth seafloor crust age 1996.gif|thumb|250px|Age of oceanic crust: youngest (red) is along spreading centres]]

'''Seafloor spreading''' happens at the bottom of an [[ocean]] as [[tectonic plate]]s move apart. The seafloor moves and carries continents with it. At ridges in the middle of oceans, new oceanic [[oceanic crust|crust]] is created. The motivating force for seafloor spreading ridges is tectonic plate pull rather than magma pressure, although there is typically significant magma activity at spreading ridges.<ref name=":0">Tan, Yen Joe, et al. "Dynamics of a seafloor-spreading episode at the East Pacific Rise." ''Nature'' 540.7632 (2016): 261-265.</ref>

At the [[Mid-Atlantic Ridge]] (and other places), material from the upper [[Mantle (geology)|mantle]] rises through the [[Fault (geology)|fault]]s between oceanic plates. It forms new crust as the plates move away from each other. The new crust then slowly moves away from the ridge. It is a place of earthquakes and volcanos. Seafloor spreading helps explain [[continental drift]] in [[plate tectonics]]. At [[oceanic trench]]es, seafloor crust slides down and under continental crust.

Earlier theories (e.g. by [[Alfred Wegener]]) of continental drift were that continents '[[plow]]ed' through the ocean. The modern idea is that the ocean floor itself moves and carries the [[continent]]s with it as it expands from a mid-ocean ridge. Today, it is accepted. The [[phenomenon]] is caused by [[convection]] in the weak upper mantle, or [[asthenosphere]].<ref>{{Cite book|title=Petrologic studies: a volume to honor A.F. Buddington|last=Hess|first=H.H.|date=1962|publisher=Geological Society of America|place=Boulder, CO|pages=599–620|chapter=History of ocean basins|accessdate=8 September 2010|chapter-url=http://www.mantleplumes.org/WebDocuments/Hess1962.pdf}}</ref><ref>{{cite journal|last1=Elsasser|first1=Walter M.|title=Sea-floor spreading as thermal convection|journal=Journal of Geophysical Research|volume=76|pages=1101–1112|year=1971|issue=5|doi=10.1029/JB076i005p01101|bibcode=1971JGR....76.1101E}}</ref>

Additionally spreading rates determine if the ridge is a fast, intermediate, or slow. As a general rule, fast ridges see spreading rate of more than 9 cm/year. Intermediate ridges have a spreading rate of 4-9 cm/year while slow spreading ridges have a rate less than 4 cm/year. <ref name=":0" />

== Mid-ocean ridge ==
A '''mid-ocean ridge''' is an [[underwater]] [[mountain range|mountain system]]. This consists of mountain chains, with a [[Rift (geology)|rift]] [[valley]] running along its [[spine]], formed by [[plate tectonics]]. A mid-ocean ridge marks the boundary between two [[tectonic plate]]s which are moving apart. A mid ocean ridge is made by a divergent boundary.

The mid-ocean ridges of the world are connected and form a single global mid-oceanic ridge system that is part of every [[ocean]]. The mid-oceanic ridge system is the longest [[mountain range]] in the [[world]]. The continuous mountain range is {{convert|65000|km|mi|-2|abbr=on}} long. It is several times longer than the [[Andes]], the longest continental mountain range. The total length of the oceanic ridge system is {{convert|80000|km|mi|-2|abbr=on}} long.<ref>''Cambridge Encyclopedia'' 2005 - Oceanic ridges</ref>

=== How it works ===
Mid-ocean ridges are geologically active, with new magma constantly emerging onto the ocean floor and into the crust at and near rifts along the ridge axes. The crystallized magma forms new crust of [[basalt]] and [[gabbro]].

The rocks making up the crust below the sea floor are youngest at the axis of the ridge and age with increasing distance from that axis. New magma of [[basalt]] composition emerges at and near the axis because of [[Igneous_rock#Decompression|decompression melting]] in the underlying [[Mantle (geology)|Earth's mantle]].<ref>{{cite book|isbn=9780412533105|author=Marjorie Wilson.|year=1993|publisher=Chapman & Hall|location=London|title=Igneous petrogenesis}}</ref>

The [[oceanic crust]] is made up of rocks much younger than the Earth itself: oceanic crust in the ocean basins is everywhere less than 200 million years old. The crust is in a constant state of 'renewal' at the ocean ridges. Moving away from the mid-ocean ridge, ocean depth progressively increases; the greatest depths are in [[ocean trench]]es. As the [[oceanic crust]] moves away from the ridge axis, the [[peridotite]] in the underlying mantle cools and becomes more rigid. The crust and the relatively rigid peridotite below it make up the oceanic [[lithosphere]].

Slow spreading ridges like the Mid-Atlantic Ridge have large, wide [[rift valley]]s, sometimes as big as 10-20 km wide and very rugged terrain at the ridge crest. By contrast, fast spreading ridges like the [[East Pacific Rise]] are narrow, sharp incisions surrounded by generally flat topography that slopes away from the ridge over many hundreds of miles.

== References ==
{{Reflist}}

[[Category:Oceanography]]
[[Category:Plate tectonics]]

Seafloor spreading - Revision history

ImportMaster at 20:25, 8 April 2022