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Igneous rocks which have a deficiency of aluminium
Chart illustrating the meaning of peralkaline, metaluminous, peraluminous and subaluminous
Peralkaline rocks include those
igneous rocks which have a deficiency of
aluminium such that
sodium and
potassium are in excess of that needed for
feldspar . The presence of
aegerine (sodium
pyroxene ) and
riebeckite (sodium
amphibole ) are indicative of peralkaline conditions. Examples are the peralkaline
rhyolites ,
comendite and
pantellerite ,
[1] with comendite being the more
felsic (
silica -rich) rock.
[2] Another example is the peralkaline
granite that forms the islet of
Rockall in the North Atlantic Ocean.
[3]
Peralkaline rocks are indicative of continental
rift -related
volcanicity (e.g. the peralkaline
rhyolites of the
East African Rift in central
Kenya ) as well as continental and oceanic
hotspot volcanicity (e.g. the peralkaline rhyolites of the
Glass House Mountains in eastern
Australia and the
Canary Islands in the
Atlantic Ocean ).
[4]
[5]
[6] Peralkaline rocks related to
subduction zone volcanicity have also been reported (e.g.
Sardinia in
Italy ).
[5] Peralkaline magmas likely form when
fractional crystallization removes a high proportion of
plagioclase relative to
mafic minerals.
See also
References
^ 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 .
^ 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 .