AFM diagram showing the relative proportions of the oxides of alkalis (A), iron (F), and magnesium (M), with arrows showing the compositional change path of the magmas in the tholeiitic and the calc-alkaline magma series (BT=tholeiitic basalt, FB=ferro-basalt, ABT=tholeiitic basaltic andesite, AT=tholeiitic andesite, D=dacite, R=rhyolite, B=basalt, AB=basaltic andesite, A=andesite; dashed line=boundary between tholeiitic and calc-alkaline compositions)
Rocks from the calc-alkaline magma series are distinguished from rocks from the tholeiitic magma series by the redox state of the magma they crystallized from. Tholeiitic magmas are reduced, and calc-alkaline magmas are oxidized, with higher oxygen fugacities. When mafic (basalt-producing) magmas crystallize, they preferentially crystallize the more magnesium-rich and iron-poor forms of the silicate minerals olivine and pyroxene, causing the iron content of tholeiitic magmas to increase as the melt is depleted of iron-poor crystals. (Magnesium-rich olivine solidifies at much higher temperatures than iron-rich olivine.) However, a calc-alkaline magma is oxidized enough to (simultaneously) precipitate significant amounts of the iron oxide magnetite, causing the iron content of the magma to remain more steady as it cools than with a tholeiitic magma.
The difference between these two magma series can be seen on an AFM diagram, a ternary diagram showing the relative proportions of the oxides of Na2O + K2O (A), FeO + Fe2O3 (F), and MgO (M). As magmas cool, they precipitate out significantly more iron and magnesium than alkali, causing the magmas to move towards the alkali corner. In tholeiitic magma, as it cools and preferentially produces magnesium-rich crystals, the magnesium content of the magma plummets, causing the magma to move away from the magnesium corner until it runs low on magnesium and begins to move towards the alkali corner as it loses iron and remaining magnesium. With the calc-alkaline series, however, the precipitation of magnetite causes the iron-magnesium ratio to remain relatively constant, so the magma moves in a straight line towards the alkali corner on the AFM diagram.
Calc-alkaline rocks typically are found in the volcanic arcs above subduction zones, commonly in island arcs, and particularly on those arcs on continental crust.
Petrologic origin
Rocks in the series are thought to be genetically related by fractional crystallization and to be at least partly derived from magmas of basalt composition formed in the Earth's mantle. Trends in composition can be explained by a variety of processes. Many explanations focus on water content and oxidation states of the magmas. Proposed mechanisms of formation begin with partial melting of subducted material and of mantle peridotite (olivine and pyroxene) altered by water and melts derived from subducted material. Mechanisms by which the calc-alkaline magmas then evolve may include fractional crystallization, assimilation of continental crust, and mixing with partial melts of continental crust.
Barker, Daniel S. (1983). Igneous Rocks. Englewood Cliffs, NJ: Prentice Hall, Inc. p. 417.
Further reading
Peacock, M. A. (1931). "Classification of igneous rock series". Journal of Geology. 39 (1): 54–67. Bibcode:1931JG.....39...54P. doi:10.1086/623788.
Rittmann, Alfred (1962). Volcanoes and their activity. New York: John Wiley & Sons, Inc. p. 305, translated by EA Vincent from the 1960, 2 ed.{{cite book}}: CS1 maint: postscript (link)
Sheth, Hetu; Torres-Alvarado, Ignacio; Verma, Surendra (August 2002). "What Is the "Calc-alkaline Rock Series"?". International Geology Review. 44 (8): 686–701. Bibcode:2002IGRv...44..686S. doi:10.2747/0020-6814.44.8.686. S2CID 129795855. Two of these widely used diagrams are the total alkalies-silica (TAS) diagram and the (Na2O + K2O)-FeO*-MgO (AFM) triangular diagram, neither of which has calcium as one of the plotting parameters... Not all orogenic andesites are calc-alkaline, and not all calc-alkaline andesites are orogenic
Le Maitre, R. W.; Streckeisen, A.; Zanettin, B.; Le Bas, M. J.; Bonin, B.; Bateman, P., eds. (January 2005). Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences, Subcommission on the Systematics of Igneous Rocks. Cambridge, UK: Cambridge University Press. p. 252. ISBN0-521-61948-3.
Arculus, Richard J. (2003). "Use and abuse of the terms calcalkaline and calcalkalic". Journal of Petrology. 44 (5): 929–935. Bibcode:2003JPet...44..929A. doi:10.1093/petrology/44.5.929. The terms calcalkaline and calcalkalic are currently defined and used in multiple and non-equivalent ways. Generally, the variation of total Fe as FeO/MgO within evolving subalkaline rock suites is regarded as the most distinctive character of calcalkaline compared with tholeiitic suites, reflecting the relative timing of phase saturation with Fe–Ti oxides, plagioclase, and ferromagnesian silicates. Other classification schemes are widely used, including a minority of adherents to the original formalized definition of 'calcalkalic' by Peacock (1931, Journal of Geology 39, 54–67). Given the prevailing contradictory and confusing usage of these terms, which leads to miscommunication, it is proposed that the spectrum of subalkaline rocks be divided into high-, medium-, and low-Fe suites, complementing divisions made on the basis of K contents. The terms calcalkaline and calcalkalic should be restricted to rock suites that conform to Peacock's definition.
February 15, 2023
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This article includes a list of references related reading or external links but its sources remain unclear because it lacks inline citations Please help to improve this article by introducing more precise citations August 2015 Learn how and when to remove this template message The calc alkaline magma series is one of two main subdivisions of the subalkaline magma series the other subalkaline magma series being the tholeiitic series A magma series is a series of compositions that describes the evolution of a mafic magma which is high in magnesium and iron and produces basalt or gabbro as it fractionally crystallizes to become a felsic magma which is low in magnesium and iron and produces rhyolite or granite Calc alkaline rocks are rich in alkaline earths magnesia and calcium oxide and alkali metals and make up a major part of the crust of the continents The diverse rock types in the calc alkaline series include volcanic types such as basalt andesite dacite rhyolite and also their coarser grained intrusive equivalents gabbro diorite granodiorite and granite They do not include silica undersaturated alkalic or peralkaline rocks Contents 1 Geochemical characterization 2 Geologic context 3 Petrologic origin 4 See also 5 References 6 Further readingGeochemical characterization Edit AFM diagram showing the relative proportions of the oxides of alkalis A iron F and magnesium M with arrows showing the compositional change path of the magmas in the tholeiitic and the calc alkaline magma series BT tholeiitic basalt FB ferro basalt ABT tholeiitic basaltic andesite AT tholeiitic andesite D dacite R rhyolite B basalt AB basaltic andesite A andesite dashed line boundary between tholeiitic and calc alkaline compositions Rocks from the calc alkaline magma series are distinguished from rocks from the tholeiitic magma series by the redox state of the magma they crystallized from Tholeiitic magmas are reduced and calc alkaline magmas are oxidized with higher oxygen fugacities When mafic basalt producing magmas crystallize they preferentially crystallize the more magnesium rich and iron poor forms of the silicate minerals olivine and pyroxene causing the iron content of tholeiitic magmas to increase as the melt is depleted of iron poor crystals Magnesium rich olivine solidifies at much higher temperatures than iron rich olivine However a calc alkaline magma is oxidized enough to simultaneously precipitate significant amounts of the iron oxide magnetite causing the iron content of the magma to remain more steady as it cools than with a tholeiitic magma The difference between these two magma series can be seen on an AFM diagram a ternary diagram showing the relative proportions of the oxides of Na2O K2O A FeO Fe2O3 F and MgO M As magmas cool they precipitate out significantly more iron and magnesium than alkali causing the magmas to move towards the alkali corner In tholeiitic magma as it cools and preferentially produces magnesium rich crystals the magnesium content of the magma plummets causing the magma to move away from the magnesium corner until it runs low on magnesium and begins to move towards the alkali corner as it loses iron and remaining magnesium With the calc alkaline series however the precipitation of magnetite causes the iron magnesium ratio to remain relatively constant so the magma moves in a straight line towards the alkali corner on the AFM diagram Calc alkaline magmas are typically hydrous Geologic context EditCalc alkaline rocks typically are found in the volcanic arcs above subduction zones commonly in island arcs and particularly on those arcs on continental crust Petrologic origin EditRocks in the series are thought to be genetically related by fractional crystallization and to be at least partly derived from magmas of basalt composition formed in the Earth s mantle Trends in composition can be explained by a variety of processes Many explanations focus on water content and oxidation states of the magmas Proposed mechanisms of formation begin with partial melting of subducted material and of mantle peridotite olivine and pyroxene altered by water and melts derived from subducted material Mechanisms by which the calc alkaline magmas then evolve may include fractional crystallization assimilation of continental crust and mixing with partial melts of continental crust See also EditAlkali basalt Alkaline magma series Igneous differentiationReferences EditBarker Daniel S 1983 Igneous Rocks Englewood Cliffs NJ Prentice Hall Inc p 417 Further reading EditPeacock M A 1931 Classification of igneous rock series Journal of Geology 39 1 54 67 Bibcode 1931JG 39 54P doi 10 1086 623788 Rittmann Alfred 1962 Volcanoes and their activity New York John Wiley amp Sons Inc p 305 translated by EA Vincent from the 1960 2 ed a href Template Cite book html title Template Cite book cite book a CS1 maint postscript link Sheth Hetu Torres Alvarado Ignacio Verma Surendra August 2002 What Is the Calc alkaline Rock Series International Geology Review 44 8 686 701 Bibcode 2002IGRv 44 686S doi 10 2747 0020 6814 44 8 686 S2CID 129795855 Two of these widely used diagrams are the total alkalies silica TAS diagram and the Na2O K2O FeO MgO AFM triangular diagram neither of which has calcium as one of the plotting parameters Not all orogenic andesites are calc alkaline and not all calc alkaline andesites are orogenic Le Maitre R W Streckeisen A Zanettin B Le Bas M J Bonin B Bateman P eds January 2005 Igneous Rocks A Classification and Glossary of Terms Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks Cambridge UK Cambridge University Press p 252 ISBN 0 521 61948 3 Arculus Richard J 2003 Use and abuse of the terms calcalkaline and calcalkalic Journal of Petrology 44 5 929 935 Bibcode 2003JPet 44 929A doi 10 1093 petrology 44 5 929 The terms calcalkaline and calcalkalic are currently defined and used in multiple and non equivalent ways Generally the variation of total Fe as FeO MgO within evolving subalkaline rock suites is regarded as the most distinctive character of calcalkaline compared with tholeiitic suites reflecting the relative timing of phase saturation with Fe Ti oxides plagioclase and ferromagnesian silicates Other classification schemes are widely used including a minority of adherents to the original formalized definition of calcalkalic by Peacock 1931 Journal of Geology 39 54 67 Given the prevailing contradictory and confusing usage of these terms which leads to miscommunication it is proposed that the spectrum of subalkaline rocks be divided into high medium and low Fe suites complementing divisions made on the basis of K contents The terms calcalkaline and calcalkalic should be restricted to rock suites that conform to Peacock s definition Retrieved from https en wikipedia org w index php title Calc alkaline magma series amp oldid 1117499714, wikipedia, wiki, book, books, library,
