Peralkaline rock

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 basin-related volcanicity, for example the peralkaline rhyolite lavas of the East African Rift in central Kenya.[4] Peralkaline magmas likely form when fractional crystallization removes a high proportion of plagioclase relative to mafic minerals.[5]

See also

References
  1. 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.
  2. McBirney, Alexander R. (1984). Igneous petrology. San Francisco, Calif.: Freeman, Cooper. p. 502. ISBN 0198578105.
  3. Sutherland, D. S. (editor) (1982). Igneous Rocks of the British Isles. Chichester: John Wiley and Sons. p. 413. ISBN 978-0-471-27810-8.CS1 maint: extra text: authors list (link)
  4. 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.
  5. McBirney 1984, pp. 396-397.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.