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Article: Origin of oceanic phonolites by crystal fractionation and the problem of the Daly gap: An example from Rarotonga

TitleOrigin of oceanic phonolites by crystal fractionation and the problem of the Daly gap: An example from Rarotonga
Authors
Issue Date2001
PublisherSpringer Verlag. The Journal's web site is located at http://link.springer.de/link/service/journals/00410/index.htm
Citation
Contributions To Mineralogy And Petrology, 2001, v. 142 n. 3, p. 336-346 How to Cite?
AbstractFelsic alkalic rocks are a minor component of many ocean island volcanic suites, and include trachyte and phonolite as well as various types of alkaline and peralkaline rhyolite. However, there is considerable debate on the nature of their formation; for example, are they formed by partial melting of anomalous mantle or the final products of fractional crystallization of mafic magmas. The phonolites and foidal phonolites on Rarotonga were formed by low pressure crystal fractionation of two chemically distinct parental magmas. Low silica and high silica mafic magmas produced a basanite foidal phonolite series and an alkali basalt-phonolite series, respectively. The foidal phonolite composition evolved from the low silica mafic magmas by approximately 60% fractionation of titanaugite + leucite + nepheline + magnetite + apatite. Fractionation continued with the crystallization of aegirine-augite + nepheline + kaersutite + magnetite + apatite. The phonolites formed from the alkali basalts by approximately 40% fractionation of kaersutite + titanaugite + Fe-Ti oxide + plagioclase + apatite and continued to evolve further by fractionation of anorthoclase + nepheline + aegerine-augite + Fe-Ti oxides. As the magmas fractionated in both suites, their overall viscosities (solid + liquid) increased until a point was reached whereby viscosity inhibited the eruption of magmas with compositions intermediate between the mafic rocks and the felsic rocks. However, the magmas continued to fractionate under static conditions with the residual fluid becoming foidal phonolitic in the low silica suite or phonolitic in the high silica suite. These phonolitic liquids, as a result of an increase in volatiles and enrichment of alkalis over aluminum, would actually have a lower viscosity than the intermediate liquids. This decrease in viscosity and the switch from a magma chamber being predominantly a liquid with suspended solids to a solid crystalline network with an interstitial liquid enabled phonolitic liquids to migrate, pool, and eventually erupt on the surface.
Persistent Identifierhttp://hdl.handle.net/10722/178221
ISSN
2015 Impact Factor: 3.218
2015 SCImago Journal Rankings: 2.582
References

 

DC FieldValueLanguage
dc.contributor.authorThompson, Gen_US
dc.contributor.authorSmith, Ien_US
dc.contributor.authorMalpas, Jen_US
dc.date.accessioned2012-12-19T09:43:30Z-
dc.date.available2012-12-19T09:43:30Z-
dc.date.issued2001en_US
dc.identifier.citationContributions To Mineralogy And Petrology, 2001, v. 142 n. 3, p. 336-346en_US
dc.identifier.issn0010-7999en_US
dc.identifier.urihttp://hdl.handle.net/10722/178221-
dc.description.abstractFelsic alkalic rocks are a minor component of many ocean island volcanic suites, and include trachyte and phonolite as well as various types of alkaline and peralkaline rhyolite. However, there is considerable debate on the nature of their formation; for example, are they formed by partial melting of anomalous mantle or the final products of fractional crystallization of mafic magmas. The phonolites and foidal phonolites on Rarotonga were formed by low pressure crystal fractionation of two chemically distinct parental magmas. Low silica and high silica mafic magmas produced a basanite foidal phonolite series and an alkali basalt-phonolite series, respectively. The foidal phonolite composition evolved from the low silica mafic magmas by approximately 60% fractionation of titanaugite + leucite + nepheline + magnetite + apatite. Fractionation continued with the crystallization of aegirine-augite + nepheline + kaersutite + magnetite + apatite. The phonolites formed from the alkali basalts by approximately 40% fractionation of kaersutite + titanaugite + Fe-Ti oxide + plagioclase + apatite and continued to evolve further by fractionation of anorthoclase + nepheline + aegerine-augite + Fe-Ti oxides. As the magmas fractionated in both suites, their overall viscosities (solid + liquid) increased until a point was reached whereby viscosity inhibited the eruption of magmas with compositions intermediate between the mafic rocks and the felsic rocks. However, the magmas continued to fractionate under static conditions with the residual fluid becoming foidal phonolitic in the low silica suite or phonolitic in the high silica suite. These phonolitic liquids, as a result of an increase in volatiles and enrichment of alkalis over aluminum, would actually have a lower viscosity than the intermediate liquids. This decrease in viscosity and the switch from a magma chamber being predominantly a liquid with suspended solids to a solid crystalline network with an interstitial liquid enabled phonolitic liquids to migrate, pool, and eventually erupt on the surface.en_US
dc.languageengen_US
dc.publisherSpringer Verlag. The Journal's web site is located at http://link.springer.de/link/service/journals/00410/index.htmen_US
dc.relation.ispartofContributions to Mineralogy and Petrologyen_US
dc.titleOrigin of oceanic phonolites by crystal fractionation and the problem of the Daly gap: An example from Rarotongaen_US
dc.typeArticleen_US
dc.identifier.emailMalpas, J: jgmalpas@hku.hken_US
dc.identifier.authorityMalpas, J=rp00059en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.scopuseid_2-s2.0-0035657361en_US
dc.identifier.hkuros69912-
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-0035657361&selection=ref&src=s&origin=recordpageen_US
dc.identifier.volume142en_US
dc.identifier.issue3en_US
dc.identifier.spage336en_US
dc.identifier.epage346en_US
dc.publisher.placeGermanyen_US
dc.identifier.scopusauthoridThompson, G=7403078084en_US
dc.identifier.scopusauthoridSmith, I=7404425799en_US
dc.identifier.scopusauthoridMalpas, J=7006136845en_US

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