Difference between revisions of "Carbonatite" - New World Encyclopedia

Latest revision as of 19:10, 26 November 2023

The carbonatite complex of Sukulu, Uganda, as seen from Tororo Rock.

Carbonatites are unusual igneous rocks that contain carbonate minerals at levels that exceed 20 percent (by volume). Their additional mineral composition may include apatite, barite, fluorite, or magnetite. Their elemental content may include barium, cesium, and rubidium, with lesser amounts of hafnium, titanium, and zirconium.

Nearly all known carbonatite deposits are intrusives—that is, they are found beneath the Earth's surface. This is because carbonatite lava flows are unstable in the atmosphere and are altered by relatively rapid reactions. Yet, exposed carbonatite lavas are not as uncommon as once thought. The study of carbonatites has helped scientists unravel a segment of geological history, and some of these rocks have provided commercially valuable quantities of minerals.

Occurrence

Carbonatites usually occur as small plugs within zoned alkalic intrusive complexes, or as dikes, sills, breccias, and veins. They are, almost exclusively, associated with continental rift-related tectonic settings. The majority of carbonatites are Proterozoic or Phanerozoic in age. It appears that there has been a steady increase in the carbonatitic igneous activity through the Earth's history, from Archean to present.

Associated igneous rocks typically include ijolite, melteigite, teschenite, lamprophyres, phonolite, foyaite, shonkinite, silica-undersaturated pyroxenite (essexite), and nepheline syenite.

Known Examples

Areas where carbonatites have been found include: Oka and St. Honore, Quebec; Iron Hill and Gem Park, Colorado; Magnet Cove igneous complex, Arkansas; Mountain Pass, California; Phalaborwa, South Africa; Jacupiranga, Brazil; Ayopaya, Bolivia; Kovdor, Russia; the Mount Weld and Mud Tank intrusive carbonatites of Australia; and the Fen Complex, Norway.

The Ol Doinyo Lengai volcano, in the Great Rift Valley in Tanzania, is the world's only active volcano that erupts natrocarbonatite lava with nearly no silicon content. It erupted the lowest temperature lava in the world, at 500-600 °C (930-1,100 °F). Other, older carbonatite volcanoes are located in the same region, including Homa Mountain.

The Mount Weld carbonatite is unassociated with a belt or suite of alkaline igneous rocks, although calc-alkaline magmas are known in the region. The genesis of this Archean carbonatite remains contentious, as it is the sole example of an Archean carbonatite in Australia.

Formation

Carbonatites are rare, peculiar igneous rocks formed by unusual processes and from unusual source rocks. Historically, these rocks were thought to be formed by the melting of limestone or marble by intrusion of magma. This mechanism, however, is discounted by geochemical and mineralogical data.

Currently, there are three models for their formation:

Direct generation by very low-degree partial melts in the mantle and melt differentiation;
Immiscibility between a carbonate melt and a silicate melt; and
Peculiar, extreme crystal fractionation.

There is evidence for each of these processes, but they all involve unusual phenomena.

Mineralogy

The primary mineral content of carbonatites is highly variable, but it may include natrolite, sodalite, sovite, apatite, magnetite, barite, fluorite, ancylite group minerals, and other rare minerals not found in more normal igneous rocks. They may also be sources of mica or vermiculite. Recognition of carbonatites may be difficult, especially as their mineralogy and texture may not differ much from marble save for the presence of igneous minerals.

Natrocarbonatite is made up largely of two minerals: nyerereite and gregoryite. Nyerereite was named after Julius Nyerere, the first president of independent Tanzania, and gregoryite was named after John Walter Gregory, one of the first geologists to study the Great Rift Valley and author of the book The Great Rift Valley. These minerals are both anhydrous carbonates rich in sodium and potassium. Upon contact with moisture in the atmosphere, they react quickly, converting the dark lava and ash to white material within a few hours.

Geochemistry

Carbonatite, if composed entirely of carbonate minerals, is extremely unusual in its major elemental composition as compared to silicate igneous rocks, because it is composed primarily of Na₂O and CaO plus CO₂.

Most carbonatites tend to include some silicate mineral fraction. Silicate minerals associated with these rocks are pyroxene, olivine, and silica-undersaturated minerals such as nepheline and other feldspathoids.

Geochemically, carbonatites are dominated by incompatible elements (Ba, Cs, Rb) and smaller amounts of compatible elements (Hf, Zr, Ti). This, together with their silica-undersaturated composition, supports inferences that carbonatites are formed by low degrees of partial melting.

Economic importance

Carbonatites may contain various elements, such as rare earth elements: copper, iron, phosphorus, niobium, uranium, thorium, titanium, barium, fluorine, and zirconium. A number of these elements are found in economically valuable concentrations.

References
ISBN links support NWE through referral fees

Blatt, Harvey, and Robert J. Tracy. 1995. Petrology: Igneous, Sedimentary, and Metamorphic, 2nd ed. New York: W.H. Freeman. ISBN 0716724383
Hawaiian Volcano Observatory. 2003. World's Coolest Lava is in Africa U.S. Geological Survey. Retrieved December 8, 2007.
McBirney, Alexander R. 2006. Igneous Petrology. 3rd ed. Jones & Bartlett. ISBN 0763734489
Pellant, Chris. 2002. Rocks and Minerals. Smithsonian Handbooks. New York: Dorling Kindersley. ISBN 0789491060
Skinner, Brian J., Stephen C. Porter, and Jeffrey Park. 2004. Dynamic Earth: An Introduction to Physical Geology. 5th ed. Hoboken, NJ: John Wiley. ISBN 0471152285
Modreski, Peter J., Theodore J. Armbrustmacher, and Donald B. Hoover. 1995. Carbonatite Deposits U.S. Geological Survey. Retrieved December 8, 2007.

External links

All links retrieved November 26, 2023.

Descriptive Model of Carbonatite Deposits U.S. Geological Survey.
Mount Weld, Western Australia

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@@ Line 1: / Line 1: @@
-'''Carbonatites''' ([[International Phonetic Alphabet|IPA]]: {{IPA|/kɑɹˈbɒnətaɪt/}}) are [[intrusive]] or extrusive [[igneous]] [[Rock (geology)|rocks]] defined by mineralogy that comprises more than 20 volume-% [[carbonate]] minerals. Carbonatites may be confused with [[marble]], and may require geochemical verification.
+{{Copyedited}}{{Images OK}}{{Submitted}}{{Approved}}{{Paid}}
+[[Image:Sukulu1.jpg|thumb|400px|The carbonatite complex of Sukulu, Uganda, as seen from Tororo Rock.]]
-Carbonatites usually occur as small plugs within zoned alkalic intrusive complexes, or as [[Dike (geology)|dike]]s, [[Sill (geology)|sill]]s, [[breccia]]s, and [[Lode|vein]]s. They are, almost exclusively, associated with continental rift-related tectonic settings. The majority of carbonatites are [[Proterozoic]] or [[Phanerozoic]] in age. It seems that there has been a steady increase in the carbonatitic igneous activity through the Earth's history, from [[Archean]] to present.
+'''Carbonatites''' are unusual [[igneous]] [[Rock (geology)|rocks]] that contain [[carbonate]] [[mineral]]s at levels that exceed 20 percent (by volume). Their additional mineral composition may include [[apatite]], [[barite]], [[fluorite]], or [[magnetite]]. Their elemental content may include [[barium]], [[cesium]], and [[rubidium]], with lesser amounts of [[hafnium]], [[titanium]], and [[zirconium]].
+{{toc}}
+Nearly all known carbonatite deposits are intrusives—that is, they are found beneath the [[Earth]]'s surface. This is because carbonatite [[lava]] flows are unstable in the atmosphere and are altered by relatively rapid reactions. Yet, exposed carbonatite lavas are not as uncommon as once thought. The study of carbonatites has helped scientists unravel a segment of geological history, and some of these rocks have provided commercially valuable quantities of minerals.
-Nearly all carbonatite occurrences are intrusives or subvolcanic intrusives. This is because carbonatite lava flows are unstable and react quickly in the atmosphere. Carbonatite lavas may not be as uncommon as thought, but have been poorly preserved throughout [[History of Earth|Earth's history]].
+== Occurrence ==
+Carbonatites usually occur as small plugs within zoned alkalic intrusive complexes, or as [[Dike (geology)|dike]]s, [[Sill (geology)|sill]]s, [[breccia]]s, and [[Lode|vein]]s. They are, almost exclusively, associated with continental rift-related tectonic settings. The majority of carbonatites are [[Proterozoic]] or [[Phanerozoic]] in age. It appears that there has been a steady increase in the carbonatitic igneous activity through the Earth's history, from [[Archean]] to present.
-Only one carbonatite volcano is known to have erupted in historical time, [[Ol Doinyo Lengai]] in [[Tanzania]]. It erupted the lowest temperature [[lava]] in the world, at 500-600 °C (930-1,100 °F). The lava is dominated by [[natrolite]] and [[trona]], sodic calcite.
+Associated igneous rocks typically include [[ijolite]], [[melteigite]], [[teschenite]], [[lamprophyre]]s, [[phonolite]], [[foyaite]], [[shonkinite]], silica-undersaturated [[pyroxenite]] ([[essexite]]), and [[nepheline syenite]].
-==Genesis==
+=== Known Examples ===
-Carbonatites are ''rare'', ''peculiar'' igneous rocks formed by unusual processes and from unusual source rocks. Three models of their formation exist:
-* direct generation by very low degree partial melts in the [[Earth's mantle|mantle]] and melt differentiation
-* liquid immiscibility between a carbonate melt and a [[silicate]] melt
-* peculiar, extreme crystal fractionation
-Evidence for each process exists, but the key is that these are unusual phenomenon. Historically, carbonatites were thought to form by melting of [[limestone]] or [[marble]] by intrusion of [[magma]], however geochemical and mineralogical data discount this.
-==Mineralogy==
+Areas where carbonatites have been found include: [[Oka, Quebec|Oka]] and [[St. Honore]], [[Quebec]]; [[Iron Hill]] and [[Gem Park]], [[Colorado]]; [[Magnet Cove igneous complex]], [[Arkansas]]; [[Mountain Pass]], [[California]]; [[Phalaborwa]], [[South Africa]]; [[Jacupiranga]], [[Brazil]]; Ayopaya, [[Bolivia]]; [[Kovdor]], [[Russia]]; the [[Mount Weld]] and [[Mud Tank]] intrusive carbonatites of [[Australia]]; and the [[Fen Complex, Norway]].
-Primary mineralogy is highly variable, but may include [[natrolite]], [[sodalite]], [[sovite]], [[apatite]], [[magnetite]], [[barite]], [[fluorite]], [[ancylite]] group minerals, and other rare, peculiar minerals not found in more normal igneous rocks. Recognition of carbonatites may be difficult, especially as their mineralogy and texture may not differ much from [[marble]] save for the presence of igneous minerals. They may also be sources of [[mica]] or [[vermiculite]].
-'''[[Natrocarbonatite]]''' is made up largely of two minerals, nyerereite (named after [[Julius Nyerere]], the first president of independent [[Tanzania]]) and gregoryite (named after [[John Walter Gregory]], one of the first geologists to study the [[Great Rift Valley]] and author of the book ''The Great Rift Valley''). These minerals are both [[carbonate]]s in which [[sodium]] and [[potassium]] are present in significant quantities. Both are [[anhydrous]] and when they come into contact with the moisture of the atmosphere, they begin to react extremely quickly.  The black or dark brown lava and ash erupted begins to turn white within a few hours.
+The [[Ol Doinyo Lengai]] volcano, in the [[Great Rift Valley]] in [[Tanzania]], is the world's only active volcano that erupts [[natrocarbonatite]] lava with nearly no [[silicon]] content. It erupted the lowest temperature [[lava]] in the world, at 500-600 °C (930-1,100 °F). Other, older carbonatite volcanoes are located in the same region, including [[Homa Mountain]].
-== Geochemistry ==
+The Mount Weld carbonatite is unassociated with a belt or suite of alkaline [[igneous rock]]s, although calc-alkaline magmas are known in the region. The genesis of this Archean carbonatite remains contentious, as it is the sole example of an Archean carbonatite in Australia.
-Carbonatite, if composed entirely of carbonate minerals, is extremely unusual in its major element composition as compared to silicate igneous rocks, obviously because it is composed primarily of Na<sub>2</sub>O and CaO plus CO<sub>2</sub>.
-Most carbonatites tend to include some silicate mineral fraction; by definition an igneous rock containing >20% carbonate minerals is classified as a carbonatite. Silicate minerals associated with such compositions are pyroxene, olivine, and silica-undersaturated minerals such as [[nepheline]] and other feldspathoids.
+== Formation ==
+Carbonatites are ''rare'', ''peculiar'' igneous rocks formed by unusual processes and from unusual source rocks. Historically, these rocks were thought to be formed by the melting of [[limestone]] or [[marble]] by intrusion of [[magma]]. This mechanism, however, is discounted by geochemical and mineralogical data.
-Geochemically, carbonatites are dominated by incompatible elements (Ba, Cs, Rb) and depletions in compatible elements (Hf, Zr, Ti). This together with their silica-undersaturated composition supports inferences that carbonatites are formed by low degrees of partial melting.
+Currently, there are three models for their formation:
+* Direct generation by very low-degree partial melts in the [[Earth's mantle|mantle]] and melt differentiation;
+* Immiscibility between a carbonate melt and a [[silicate]] melt; and
+* Peculiar, extreme crystal fractionation.
+There is evidence for each of these processes, but they all involve unusual phenomena.
-== Occurrence ==
+==Mineralogy==
-Associated igneous rocks typically include [[ijolite]], [[melteigite]], [[teschenite]], [[lamprophyre]]s, [[phonolite]], [[foyaite]], [[shonkinite]], silica undersaturated foid-bearing [[pyroxenite]] ([[essexite]]), and [[nepheline syenite]].
+The primary mineral content of carbonatites is highly variable, but it may include [[natrolite]], [[sodalite]], [[sovite]], [[apatite]], [[magnetite]], [[barite]], [[fluorite]], [[ancylite]] group minerals, and other rare minerals not found in more normal igneous rocks. They may also be sources of [[mica]] or [[vermiculite]]. Recognition of carbonatites may be difficult, especially as their mineralogy and texture may not differ much from [[marble]] save for the presence of igneous minerals.
-Carbonatites are typically associated with undersaturated igneous rocks that are [[miaskitic]] (nearly [[peralkaline]]) rather than [[agpaitic]] (peralkaline).
+''[[Natrocarbonatite]]'' is made up largely of two minerals: nyerereite and gregoryite. Nyerereite was named after [[Julius Nyerere]], the first president of independent [[Tanzania]], and gregoryite was named after [[John Walter Gregory]], one of the first geologists to study the [[Great Rift Valley]] and author of the book ''The Great Rift Valley''. These minerals are both [[anhydrous]] [[carbonate]]s rich in [[sodium]] and [[potassium]]. Upon contact with moisture in the [[atmosphere]], they react quickly, converting the dark lava and ash to white material within a few hours.
-The Mount Weld carbonatite is unassociated with a belt or suite of alkaline igneous rocks, although calc-alkaline magmas are known in the region. The genesis of this Archaean carbonatite remains contentious as it is the sole example of an Archaean carbonatite in Australia.
+== Geochemistry ==
+Carbonatite, if composed entirely of carbonate minerals, is extremely unusual in its major elemental composition as compared to silicate igneous rocks, because it is composed primarily of Na<sub>2</sub>O and CaO plus CO<sub>2</sub>.
-=== Intrusive morphology ===
+Most carbonatites tend to include some silicate mineral fraction. Silicate minerals associated with these rocks are [[pyroxene]], [[olivine]], and silica-undersaturated minerals such as [[nepheline]] and other feldspathoids.
-Carbonatite is known to form in association with concentrically zoned complexes of alkaline-igneous rocks, the typical example of this being Phalaborwa, South Africa.
-Chilean carbonatites take the form of sills, lopoliths and rare dykes are reported in the Guyana Shield.
+Geochemically, carbonatites are dominated by incompatible elements (Ba, Cs, Rb) and smaller amounts of compatible elements (Hf, Zr, Ti). This, together with their silica-undersaturated composition, supports inferences that carbonatites are formed by low degrees of partial melting.
-The Mud Tank and Mount Weld carbonatites take the form of multi-stage cylindrical intrusive bodies with several distinct phases of carbonatite intrusion. Smaller carbonatite sills and dykes are present in other [[Proterozoic]] mobile belts in Australia, typically as dykes and discontinuous pods.
-=== Known Examples ===
-Carbonatites are known from [[Oka, Quebec|Oka]] and [[St. Honore]], [[Quebec]]; [[Iron Hill]] and [[Gem Park]], [[Colorado]]; [[Magnet Cove igneous complex]], [[Arkansas]];
-[[Mountain Pass]], [[California]]; [[Phalaborwa]], [[South Africa]];
-[[Jacupiranga]], [[Brazil]]; Ayopaya, [[Bolivia]]; [[Kovdor]], [[Russia]], from [[India]]; the [[Mount Weld]] and [[Mud Tank]] intrusive carbonatites [[Australia]]; the [[Fen Complex, Norway]].
-The [[Ol Doinyo Lengai]] volcano, in the [[Great Rift Valley]], Africa, is the world's only active carbonatite volcano.  Other older carbonatite volcanoes are located in the same region, including [[Homa Mountain]].
 == Economic importance ==
-Carbonatites may contain economic or anomalous concentrations of [[rare earth]] elements, [[phosphorus]], [[niobium]], [[uranium]], [[thorium]], [[copper]], [[iron]], [[titanium]], [[barium]], [[fluorine]], [[zirconium]], and other rare or incompatible elements.
+Carbonatites may contain various elements, such as [[rare earth]] elements: [[copper]], [[iron]], [[phosphorus]], [[niobium]], [[uranium]], [[thorium]], [[titanium]], [[barium]], [[fluorine]], and [[zirconium]]. A number of these elements are found in economically valuable concentrations.
-Vein deposits of [[thorium]], [[fluorite]], or [[rare earth]] elements may be associated with carbonatites, and may be hosted internal to or in the aureole of a carbonatite.
 ==References==
-* Duncan R K, Willett G C  (1990) - Mount Weld Carbonatite: in ''Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea'' The AusIMM, Melbourne  Mono 14, v1 pp 591-597
+* Blatt, Harvey, and Robert J. Tracy. 1995. ''Petrology: Igneous, Sedimentary, and Metamorphic'', 2nd ed. New York: W.H. Freeman. ISBN 0716724383
-*{{cite web|title=Carbonatite Deposits|work=[[USGS]] Carbonatite Deposits|url=http://pubs.usgs.gov/of/1995/ofr-95-0831/CHAP6.pdf|accessdate=January 31|accessyear=2005}}
+* Hawaiian Volcano Observatory. 2003. [http://hvo.wr.usgs.gov/volcanowatch/2003/03_04_17.html World's Coolest Lava is in Africa] ''U.S. Geological Survey''. Retrieved December 8, 2007.
-*{{cite web|title=DESCRIPTIVE MODEL OF CARBONATITE DEPOSITS|work=USGS DESCRIPTIVE MODEL OF CARBONATITE DEPOSITS|url=http://pubs.usgs.gov/bul/b1693/html/bull5rsj.htm|accessdate=January 31|accessyear=2005}}
+* McBirney, Alexander R. 2006. ''Igneous Petrology''. 3rd ed. Jones & Bartlett. ISBN 0763734489
-*{{cite web|title= World's Coolest Lava is in Africa|work=Volcano Watch [[April 17]], [[2003]]|url=http://hvo.wr.usgs.gov/volcanowatch/2003/03_04_17.html|accessdate=January 31|accessyear=2005}}
+* Pellant, Chris. 2002. ''Rocks and Minerals''. Smithsonian Handbooks. New York: Dorling Kindersley. ISBN 0789491060
-*[http://www.min.tu-clausthal.de/www/lager/mrbl/pdf/Schultz%20et%20al_2004.pdf Bolivian carbonatite occurrences]
+* Skinner, Brian J., Stephen C. Porter, and Jeffrey Park. 2004. ''Dynamic Earth: An Introduction to Physical Geology''. 5th ed. Hoboken, NJ: John Wiley. ISBN 0471152285
+* Modreski, Peter J., Theodore J. Armbrustmacher, and Donald B. Hoover. 1995. [http://pubs.usgs.gov/of/1995/ofr-95-0831/CHAP6.pdf Carbonatite Deposits] ''U.S. Geological Survey''. Retrieved December 8, 2007.
 ==External links==
-* [http://it.stlawu.edu/~cnya/lenweb3b.htm Photos of natrocarbonatite lava]
+All links retrieved November 26, 2023.
-*[http://volcano.und.nodak.edu/vwdocs/volc_images/africa/ol_doinyo.html Ol Doinyo Lengai, Tanzania]
+* [http://pubs.usgs.gov/bul/b1693/html/bull5rsj.htm Descriptive Model of Carbonatite Deposits] ''U.S. Geological Survey''.
-*[http://www.mtsu.edu/~fbelton/lengai.html OL DOINYO LENGAI - THE MOUNTAIN OF GOD]
+* [http://www.portergeo.com.au/database/mineinfo.asp?mineid=mn770 Mount Weld, Western Australia]
-* [http://www.koeln.netsurf.de/~w.steffens/latam.htm List of alkaline rock occurrences in the Americas]
-* [http://www.australianminesatlas.gov.au/info/aimr/phosphate.jsp Phosphate deposits of Australia, Mount Weld Carbonatite]
-* [http://www.portergeo.com.au/database/mineinfo.asp?mineid=mn770 Description of the Mount Weld Carbonatite]
-* [http://www.commerceresources.com/i/pdf/FirResourceEstimate_March62003.pdf Blue River Carbonatites, British Columbia, Canada]
-[[Category:Igneous rocks]]
+[[Category:Physical sciences]]
-[[Category:Volcanology]]
+[[Category:Earth sciences]]
-[[Category:Petrology]]
+[[Category:Geology]]
-[[et:Karbonatiit]]
+{{credit|127520278}}
-[[fr:Carbonatite]]
-[[it:Carbonatite]]
-[[ja:カーボナタイト]]
-[[sk:Karbonatit]]
-[[fi:Karbonatiitti]]