Igneous rocks which have a deficiency of aluminium
Chart illustrating the meaning of peralkaline, metaluminous, peraluminous and subaluminous Peralkaline rocks include thoseigneous rocks which have a deficiency ofaluminium such thatsodium andpotassium are in excess of that needed forfeldspar . The presence ofaegerine (sodiumpyroxene ) andriebeckite (sodiumamphibole ) are indicative of peralkaline conditions. Examples are the peralkalinerhyolites ,comendite andpantellerite ,[ 1] felsic (silica -rich) rock.[ 2] granite that forms the islet ofRockall in the North Atlantic Ocean.[ 3]
Peralkaline rocks are indicative of continentalrift -relatedvolcanicity (e.g. the peralkalinerhyolites of theEast African Rift in centralKenya ) as well as continental and oceanichotspot volcanicity (e.g. the peralkaline rhyolites of theGlass House Mountains in easternAustralia and theCanary Islands in theAtlantic Ocean ).[ 4] [ 5] [ 6] subduction zone volcanicity have also been reported (e.g.Sardinia inItaly ).[ 5] fractional crystallization removes a high proportion ofplagioclase relative tomafic minerals.[ 7]
^ Philpotts, Anthony R.; Ague, Jay J. (2009).Principles of igneous and metamorphic petrology (2nd ed.). Cambridge, UK: Cambridge University Press. pp. 143– 146.ISBN 9780521880060 ^ McBirney, Alexander R. (1984).Igneous petrology . San Francisco, Calif.: Freeman, Cooper. p. 502.ISBN 0198578105 ^ Sutherland, D. S. (editor) (1982).Igneous Rocks of the British Isles . Chichester: John Wiley and Sons. p. 413.ISBN 978-0-471-27810-8 {{cite book }}:|author= has generic name (help )^ Scaillet, Bruno; Macdonald, Ray (2003)."Experimental Constraints on the Relationships between Peralkaline Rhyolites of the Kenya Rift Valley" .Journal of Petrology .44 (10):1867– 1894.Bibcode :2003JPet...44.1867S .doi :10.1093/petrology/egg062 ^a b Shao, Fengli; Niu, Yaoling; Regelous, Marcel; Zhu, Di-Cheng (2015). "Petrogenesis of peralkaline rhyolites in an intra-plate setting: Glass House Mountains, southeast Queensland, Australia".Lithos 216 .Elsevier :196– 210.Bibcode :2015Litho.216..196S .doi :10.1016/j.lithos.2014.12.015 .ISSN 0024-4937 . ^ Troll, Valentin R.; Schmincke, Hans-Ulrich (2002)."Magma Mixing and Crustal Recycling Recorded in Ternary Feldspar from Compositionally Zoned Peralkaline 'A', Gran Canaria, Canary Islands" .Journal of Petrology 43 (2). Oxford Academic Journals: 246.doi :10.1093/petrology/43.2.243 ISSN 0022-3530 . ^ McBirney 1984 , pp. 396–397.
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