View source for Rock cycle

{{Short description|Transitional concept of geologic time}}
{{more footnotes needed|date=January 2014}}
[[File:Rock_cycle_diagram.png|thumb|300x300px|Diagram of the rock cycle]]
[[File:Rock cycle nps.PNG|thumb|upright=1.5| {{center|The rock cycle and [[plate tectonics]]<ref>{{cite web |title=The Rock Cycle |url=https://education.nationalgeographic.org/resource/rock-cycle/ |website=National Geographic |publisher=Education National Geographic |access-date=8 May 2023}}</ref>}}]]
[[File:Rough diamond.jpg|thumb|upright=1.15|This [[diamond]] is a mineral from within an igneous or metamorphic rock that formed at high temperature and pressure]]
The ''rock cycle'' is a basic concept in [[geology]] that describes transitions through [[geologic time]] among the three main [[rock (geology)|rock]] types: [[sedimentary]], [[metamorphic rock|metamorphic]], and [[igneous]]. Each rock type is altered when it is forced out of its equilibrium conditions. For example, an igneous rock such as [[basalt]] may break down and dissolve when exposed to the [[Earth's atmosphere|atmosphere]], or melt as it is [[subduction|subducted]] under a [[continent]]. Due to the driving forces of the rock cycle, [[plate tectonics]] and the [[water cycle]], rocks do not remain in equilibrium and change as they encounter new environments. The rock cycle explains how the three rock types are related to each other, and how processes change from one type to another over time. This cyclical aspect makes rock change a geologic cycle and, on [[planet]]s containing [[life]], a [[biogeochemical cycle]].

[[File:Igneous structures.jpg|thumb|upright=1.15|Structures of Igneous Rock. Legend: A = [[magma chamber]] (batholith); B = [[Dike (geology)|dyke]]/dike; C = [[laccolith]]; D = [[pegmatite]]; E = [[sill (geology)|sill]]; F = [[stratovolcano]]; '''processes''': 1 = newer intrusion cutting through older one; 2 = [[xenolith]] or roof pendant; 3 = contact metamorphism; 4 = uplift due to laccolith emplacement.]]

== Transition to igneous rock ==
When rocks are pushed deep under the [[Earth]]'s surface, they may melt into [[magma]]. If the conditions no longer exist for the magma to stay in its liquid state, it cools and solidifies into an igneous rock. A rock that cools within the Earth is called [[Intrusive rock|intrusive]] or plutonic and cools very slowly, producing a coarse-grained texture such as the rock [[granite]]. As a result of [[volcanic]] activity, magma (which is called lava when it reaches Earth's surface) may cool very rapidly on the Earth's surface exposed to the [[Earth's atmosphere|atmosphere]] and are called [[extrusive]] or volcanic rocks. These rocks are fine-grained and sometimes cool so rapidly that no crystals can form and result in a natural [[glass]], such as [[obsidian]], however the most common fine-grained rock would be known as [[basalt]]. Any of the three main types of rocks (igneous, sedimentary, and metamorphic rocks) can melt into magma and cool into igneous rocks.<ref>{{cite book |last1=Le Maitre |first1=R. W. |last2=Streckeisen |first2=A. |last3=Zanettin |first3=B. |last4=Le Bas |first4=M. J. |last5=Bonin |first5=B. |last6=Bateman |first6=P. |title=Igneous Rocks: A Classification and Glossary of Terms |date=January 2005 |publisher=Cambridge University Press |location=Cambridge, U.K. |isbn=0521619483 |edition=2nd |bibcode=2005ircg.book.....L}}</ref>

=== Secondary changes ===
Epigenetic change (secondary processes occurring at low temperatures and low pressures) may be arranged under a number of headings, each of which is typical of a group of rocks or rock-forming [[mineral]]s, though usually more than one of these alterations is in progress in the same rock. [[Silicification]], the replacement of the minerals by crystalline or crypto-crystalline silica, is most common in [[felsic]] rocks, such as [[rhyolite]], but is also found in serpentine, etc. [[Kaolinization]] is the decomposition of the [[feldspar]]s, which are the most common minerals in igneous rocks, into [[kaolin]] (along with quartz and other [[clay minerals]]); it is best shown by [[granite]]s and [[syenite]]s. [[Serpentinization]] is the alteration of [[olivine]] to [[Serpentine group|serpentine]] (with [[magnetite]]); it is typical of [[peridotite]]s, but occurs in most of the [[mafic]] rocks. In [[uralitization]], secondary [[hornblende]] replaces [[augite]]; [[chloritization]] is the alteration of augite (biotite or hornblende) to [[Chlorite group|chlorite]], and is seen in many [[diabase]]s, [[diorite]]s and [[Greenschist|greenstones]]. [[Epidosite|Epidotization]] occurs also in rocks of this group, and consists in the development of [[epidote]] from biotite, hornblende, augite or plagioclase feldspar.<ref>{{EB1911|wstitle=Petrology |volume=21 |page=331 |inline=1 |first=John Smith |last=Flett}}</ref>

== Transition to metamorphic rock ==
Rocks exposed to high temperatures and pressures can be changed physically or chemically to form a different rock, called metamorphic. Regional metamorphism refers to the effects on large masses of rocks over a wide area, typically associated with mountain building events within [[orogeny|orogenic belts]]. These rocks commonly exhibit distinct bands of differing mineralogy and colors, called [[Foliation (geology)|foliation]]. Another main type of metamorphism is caused when a body of rock comes into contact with an igneous intrusion that heats up this surrounding [[country rock (geology)|country rock]]. This ''contact metamorphism'' results in a rock that is altered and re-crystallized by the extreme heat of the magma and/or by the addition of fluids from the magma that add chemicals to the surrounding rock ([[metasomatism]]). Any pre-existing type of rock can be modified by the processes of metamorphism.<ref>{{cite book |last1=Bucher |first1=Kurt |last2=Grapes |first2=Rodney |title=Petrogenesis of Metamorphic Rocks |date=27 June 2011 |publisher=Springer Science & Business Media |isbn=978-3-540-74169-5 |url=https://books.google.com/books?id=4Ldml-A8oeUC&q=define+metamorphic+rock&pg=PA8 |access-date=8 May 2023 |language=en}}</ref><ref>{{cite web |title=Sedimentary Rocks |website=National Geographic |publisher=Education National Geographic |url=https://education.nationalgeographic.org/resource/sedimentary-rock/ |access-date=8 May 2023}}</ref>

== Transition to sedimentary rock ==
Rocks exposed to the [[Earth's atmosphere|atmosphere]] are variably unstable and subject to the processes of [[weathering]] and [[erosion]]. Weathering and erosion break the original rock down into smaller fragments and carry away dissolved material. This fragmented material accumulates and is buried by additional material. While an individual grain of sand is still a member of the class of rock it was formed from, a rock made up of such grains fused together is sedimentary. Sedimentary rocks can be formed from the [[lithification]] of these buried smaller fragments ([[clastic]] sedimentary rock), the accumulation and lithification of material generated by living [[organism]]s ([[biogenic]] sedimentary rock - [[fossil]]s), or lithification of chemically precipitated material from a mineral bearing solution due to [[evaporate|evaporation]] ([[precipitate]] sedimentary rock). Clastic rocks can be formed from fragments broken apart from larger rocks of any type, due to processes such as [[erosion]] or from organic material, like plant remains. Biogenic and precipitate rocks form from the deposition of minerals from chemicals dissolved from all other rock types.

==Forces that drive the rock cycle==

===Plate tectonics===
{{main article|Plate Tectonics}}
In 1967, J. Tuzo Wilson published an article in Nature describing the repeated opening and closing of ocean basins, in particular focusing on the current [[Atlantic Ocean]] area. This concept, a part of the plate tectonics revolution, became known as the ''Wilson cycle''. The Wilson cycle has had profound effects on the modern interpretation of the rock cycle as plate tectonics became recognized as the driving force for the rock cycle.

====Spreading ridges====
At the [[mid-ocean ridge|mid-ocean divergent boundaries]] ''new'' [[magma]] is produced by [[Earth's mantle|mantle]] upwelling and a shallow ''melting zone''. This ''juvenile'' [[basalt]]ic magma is an early phase of the igneous portion of the cycle. As the [[tectonic plates]] on either side of the ridge move apart the new rock is carried away from the ridge, the interaction of heated circulating [[seawater]] through [[Fracture (geology)|fractures]] starts the [[retrograde metamorphism]] of the new rock.

====Subduction zones====
{{main article|Subduction}}

The new basaltic [[oceanic crust]] eventually meets a [[subduction]] zone as it moves away from the spreading ridge. As this crust is pulled back into the mantle, the increasing pressure and temperature conditions cause a restructuring of the mineralogy of the rock, this metamorphism alters the rock to form [[eclogite]]. As the slab of basaltic crust and some included sediments are dragged deeper, water and other more [[Volatility (chemistry)|volatile]] materials are driven off and rise into the overlying wedge of rock above the subduction zone, which is at a lower pressure. The lower pressure, high temperature, and now volatile rich material in this wedge melts and the resulting buoyant magma rises through the overlying rock to produce [[island arc]] or [[continental margin]] [[volcanism]]. This volcanism includes more silicic lavas the further from the edge of the island arc or continental margin, indicating a deeper source and a more differentiated magma.

At times some of the metamorphosed downgoing slab may be thrust up or [[obduction|obducted]] onto the continental margin. These blocks of mantle [[peridotite]] and the metamorphic eclogites are exposed as [[ophiolite]] complexes.

The newly erupted volcanic material is subject to rapid erosion depending on the climate conditions. These sediments accumulate within the basins on either side of an island arc. As the sediments become more deeply buried lithification begins and sedimentary rock results.

====Continental collision====
On the closing phase of the classic Wilson cycle, two continental or smaller terranes meet at a convergent zone.<ref>{{cite journal |last1=Burke |first1=Kevin |last2=Dewey |first2=John F |title=Hot Spots and Continental Break-up: Implications for Collisional Orogeny |journal=Geology |date=1974 |volume=2 |issue=2 |pages=57–60 |doi=10.1130/0091-7613(1974)2<57:HSACBI>2.0.CO;2 |bibcode=1974Geo.....2...57D |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/2/2/57/205458/Hot-Spots-and-Continental-Break-up-Implications |access-date=8 May 2023|url-access=subscription }}</ref> As the two masses of [[continental crust]] meet, neither can be subducted as they are both ''low density'' silicic rock. As the two masses meet, tremendous compressional forces distort and modify the rocks involved.<ref name="Plate Tectonics, the Wilson Cycle, and Mantle Plumes: Geodynamics from the Top">{{cite journal |last1=Burke |first1=Kevin |title=Plate Tectonics, the Wilson Cycle, and Mantle Plumes: Geodynamics from the Top |journal=Annual Review of Earth and Planetary Sciences |date=30 May 2011 |volume=39 |issue=1 |pages=1–29 |doi=10.1146/annurev-earth-040809-152521 |bibcode=2011AREPS..39....1B |language=en |issn=0084-6597|doi-access=free }}</ref> The result is regional metamorphism within the interior of the ensuing [[orogeny]] or mountain building event. As the two masses are compressed, folded and faulted into a mountain range by the continental collision the whole suite of pre-existing igneous, volcanic, sedimentary and earlier metamorphic rock units are subjected to this new metamorphic event.

====Accelerated erosion====
The high mountain ranges produced by continental collisions are immediately subjected to the forces of erosion.<ref>{{cite journal |last1=Robl |first1=J. |last2=Hergarten |first2=S. |last3=Prasicek |first3=G. |title=Glacial erosion promotes high mountains on thin crust |journal=Earth and Planetary Science Letters |date=15 May 2020 |volume=538 |pages=116196 |doi=10.1016/j.epsl.2020.116196 |bibcode=2020E&PSL.53816196R |s2cid=216238429 |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X20301394#preview-section-snippets |access-date=8 May 2023 |language=en |issn=0012-821X|url-access=subscription }}</ref> Erosion wears down the mountains and massive piles of sediment are developed in adjacent ocean margins, shallow seas, and as continental deposits. As these sediment piles are buried deeper they become lithified into sedimentary rock. The metamorphic, igneous, and sedimentary rocks of the mountains become the new piles of sediments in the adjoining basins and eventually become sedimentary rock.

====An evolving process====
The plate tectonics rock cycle is an evolutionary process. Magma generation, both in the spreading ridge environment and within the wedge above a subduction zone, favors the eruption of the more silicic and volatile rich fraction of the crustal or [[upper mantle (Earth)|upper mantle]] material.<ref name="Magma Genesis, Plate Tectonics, and Chemical Differentiation of the Earth">{{cite journal |last1=Wyllie |first1=Peter J |title=Magma Genesis, Plate Tectonics, and Chemical Differentiation of the Earth |journal=Reviews of Geophysics |date=August 1988 |volume=26 |issue=3 |pages=370–404 |doi=10.1029/RG026i003p00370 |bibcode=1988RvGeo..26..370W |url=https://core.ac.uk/download/pdf/216201152.pdf |access-date=8 May 2023}}</ref> This lower density material tends to stay within the crust and not be subducted back into the mantle.<ref name="Chapter 2 - Offshore Geology and Operations">{{cite book |last1=Speight |first1=James G |title=Subsea and Deepwater Oil and Gas Science and Technology |date=2015 |publisher=Gulf Professional Publishing |location=Wyoming |isbn=9781856175586 |pages=45–70 |url=https://www.sciencedirect.com/science/article/pii/B9781856175586000027 |access-date=8 May 2023}}</ref> The magmatic aspects of plate tectonics tends to gradual segregation within or between the mantle and crust. As magma forms, the initial melt is composed of the more silicic phases that have a lower melting point. This leads to partial melting and further segregation of the [[lithosphere]]. In addition the silicic continental crust is relatively buoyant and is not usually subducted back into the mantle. So over time the continental masses grow larger and larger.<ref name="Vigneresse_etal_1996">{{cite journal |last1=Vigneresse |first1=Jean Louis |last2=Barbey |first2=Pierre |last3=Cuney |first3=Michel |title=Rheological Transitions During Partial Melting and Crystallization with Application to Felsic Magma Segregation and Transfer |journal=Journal of Petrology |date=1996 |volume=37 |issue=6 |pages=1579–1600 |doi=10.1093/petrology/37.6.1579|doi-access=free }}</ref>

===The role of water===
{{main article|Water cycle}}

The presence of abundant [[water (molecule)|water]] on Earth is of great importance for the rock cycle. Most obvious perhaps are the water driven processes of [[weathering]] and [[erosion]]. Water in the form of precipitation and [[acid]]ic [[soil]] water and [[groundwater]] is quite effective at dissolving minerals and rocks, especially those igneous and metamorphic rocks and marine sedimentary rocks that are unstable under near surface and atmospheric conditions. The water carries away the [[ion]]s dissolved in solution and the broken-down fragments that are the products of weathering. Running water carries vast amounts of sediment in rivers back to the ocean and inland basins. The accumulated and buried sediments are converted back into rock.

A less obvious role of water is in the metamorphism processes that occur in fresh seafloor volcanic rocks as seawater, sometimes heated, flows through the fractures and crevices in the rock. All of these processes, illustrated by [[serpentinite|serpentinization]], are an important part of the destruction of volcanic rock.<ref>{{cite book |last1=Joseph |first1=Antony |title=Investigating Seafloors and Oceans: From Mud Volcanoes to Giant Squid |chapter=Chapter 6 - Seafloor Hot Chimneys and Cold Seeps: Mysterious Life Around Them |date=2017 |publisher=Elsevier |location=Amsterdam, Netherlands |isbn=9780128093573 |pages=307–375 |doi=10.1016/B978-0-12-809357-3.00006-0}}</ref>

The role of water and other volatiles in the melting of existing crustal rock in the wedge above a subduction zone is a most important part of the cycle. Along with water, the presence of [[carbon dioxide]] and other carbon compounds from abundant marine [[limestone]] within the sediments atop the down going slab is another source of melt inducing volatiles. This involves the [[carbon cycle]] as a part of the overall rock cycle.<ref name="Carbon Cycle">{{cite web |title=The Slow Carbon Cycle |url=https://earthobservatory.nasa.gov/features/CarbonCycle/page2.php |website=earthobservatory.nasa.gov |access-date=8 May 2023 |date=16 June 2011}}</ref>

==See also==
{{portal|Geology}}
*{{annotated link|Migmatite}}

==References==
{{reflist}}

== Further reading ==
*{{cite book |author1=Blatt, Harvey |author2=Robert J. Tracy
 |name-list-style=amp | title=Petrology; Igneous, Sedimentary, and Metamorphic, 2nd Ed.
| publisher=W. H. Freeman
| year=1996 | isbn=0-7167-2438-3}}
*Fichter, Lynn S., (2000), ''[http://csmres.jmu.edu/geollab/Fichter/Wilson/Wilson.html The Wilson Cycle and a Plate Tectonic Rock Cycle]'', James Madison University, Department of Geology and Environmental Science. Retrieved 18 Aug. 2005.
*{{cite book |author1=Plummer, Charles |author2=McGeary, David |author3=Carlson, Diane | title=Physical Geology 
| publisher=Mc Graw Hill
| year=2005 | isbn=0-07-293353-4}}

==External links==
*[https://web.archive.org/web/20060220043153/http://rst.gsfc.nasa.gov/Sect2/Sect2_1a.html The Six Fundamental Concepts about the Earth's Geology - NASA]
*[http://csmres.jmu.edu/geollab/Fichter/Wilson/Wilson.html Wilson cycle - a detailed Plate Tectonics rock cycle]
*[https://web.archive.org/web/20050708023848/http://www.acad.carleton.edu/curricular/GEOL/DaveSTELLA/Rock%20Cycle/rock_cycle.htm Modelling the rock cycle with STELLA]
*[https://web.archive.org/web/20050422024844/http://geowords.com/histbooknetscape/j23.htm Wilson cycle]
*{{cite web|title=A circular Wilson cycle?|date=2000-09-05 |url=http://csmres.jmu.edu/geollab/Fichter/Wilson/wilsoncircl.html |url-status=dead |archive-date=2005-08-30 |archive-url=https://web.archive.org/web/20050830051034/http://csmres.jmu.edu/geollab/fichter/Wilson/wilsoncircl.html}}

{{Biogeochemical cycle}}

[[Category:Biogeochemical cycle]]
[[Category:Geological processes]]
[[Category:Petrology]]