The Open UniversitySkip to content
 

Distribution of gallium between phenocrysts and melt in peralkaline salic volcanic rocks, Kenya Rift Valley

Macdonald, R.; Rogers, N. W.; Bagiński, B. and Dzierżanowski, P. (2010). Distribution of gallium between phenocrysts and melt in peralkaline salic volcanic rocks, Kenya Rift Valley. Mineralogical Magazine, 74(2) pp. 351–363.

DOI (Digital Object Identifier) Link: http://dx.doi.org/10.1180/minmag.2010.074.2.351
Google Scholar: Look up in Google Scholar

Abstract

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
ISSN: 0026-461X
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)
Item ID: 22352
Depositing User: Nick Rogers
Date Deposited: 20 Jul 2010 10:39
Last Modified: 23 Nov 2012 13:53
URI: http://oro.open.ac.uk/id/eprint/22352
Share this page:

Altmetrics

Scopus Citations

Actions (login may be required)

View Item
Report issue / request change

Policies | Disclaimer

© The Open University   + 44 (0)870 333 4340   general-enquiries@open.ac.uk