calc-alkaline

A Dictionary of Earth Sciences | 1999 | 700+ words | Copyright

calc-alkaline The name given to a suite of rocks comprising the volcanic association basalt-andesite-dacite-rhyolite, or the plutonic association gabbro-diorite-granodiorite-granite. The suite is defined chemically using a graph depicting the variation of CaO and (Na₂O + K₂O) with SiO₂ (wt.%), and is classified as calc-alkaline if the SiO₂ value at the intersection of the CaO and (Na₂O + K₂O) trends is between 56 and 61 SiO₂ wt.%. (Less than 51 SiO₂ wt. % and the rock suite is classed as belonging to the alkalic series, 51–56 SiO₂ wt. % to the alkali-calcic series, and more than 61 SiO₂ wt. % to the calcic series.) Calc-alkaline rocks are typically developed on the continental side of plate subduction zones, well-known examples occurring in the Andes of S. America and in Japan.

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AILSA ALLABY and MICHAEL ALLABY. "calc-alkaline." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>.

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AILSA ALLABY and MICHAEL ALLABY. "calc-alkaline." A Dictionary of Earth Sciences. 1999. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-calcalkaline.html

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