Macdonald, R.; Rogers, N. W.; Bagiński, B. and Dzierżanowski, P.
|DOI (Digital Object Identifier) Link:||http://doi.org/10.1180/minmag.2010.074.2.351|
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Gallium abundances, determined bylaser ablation-inductively coupled plasma-mass spectrometry, are presented for phenocrysts and glassy matrices from a metaluminous trachyte and five peralkaline rhyolites from the Greater Olkaria Volcanic Complex, Kenya Rift Valley. Abundances in the glasses range from 28.9 to 33.3 ppm, comparable with peralkaline rhyolites elsewhere. Phenocryst Ga abundances (in ppm) are: sanidine 31.545.3; fayalite 0.020.22; hedenbergite 3.36.3; amphibole 12; biotite 72; ilmenite 0.560.72; titanomagnetite 32; chevkinite-(Ce) 364. The mafic phases and chevkinite-(Ce) are enriched in Ga relative to Al, whereas Ga/Al ratios in sanidine are smaller than in coexisting glass. Apparent partition coefficients range from <0.01 in fayalite to 12 in chevkinite-(Ce). Coefficients for hedenbergite, ilmenite and titanomagnetite decrease as melts become peralkaline. The sharp increase in Ga/Al in the more fractionated members of alkaline magmatic suites probablyresults from alkali feldspar-dominated fractionation. Case studies are presented to show that the Ga/Al ratio maybe a sensitive indicator of such petrogenetic processes as magma mixing, interaction of melts with F-rich volatile phases, mineral accumulation and volatile-induced crustal anatexis.
|Item Type:||Journal Article|
|Copyright Holders:||2010 The Mineralogical Society|
|Keywords:||gallium; magma mixing; volatile-induced anatexis; Kenya Rift Valley; peralkaline|
|Academic Unit/Department:||Science > Environment, Earth and Ecosystems
|Interdisciplinary Research Centre:||Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)|
|Depositing User:||Nick Rogers|
|Date Deposited:||20 Jul 2010 10:39|
|Last Modified:||15 Jan 2016 13:54|
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