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Distribution of germanium between phenocrysts and melt in peralkaline rhyolites from the Kenya Rift Valley

Published online by Cambridge University Press:  05 July 2018

R. Macdonald ,
N. W. Rogers  and
A. G. Tindle
R. Macdonald*
Affiliation:
Faculty of Geology, University of Warsaw, Al. Żwirki i Wigury 93, 02-089 Warsaw, Poland
N. W. Rogers
Affiliation:
Department of Earth Sciences, CESPAR, Open University, Milton Keynes MK7 6AA, UK
A. G. Tindle
Affiliation:
Department of Earth Sciences, CESPAR, Open University, Milton Keynes MK7 6AA, UK
*
E-mail: [email protected]
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Abstract

Germanium abundances, determined by laser ablation-inductively coupled plasma-mass spectrometry, are presented for phenocrysts and glass matrices from a metaluminous trachyte and four peralkaline rhyolites from the Greater Olkaria Volcanic Complex, Kenya Rift Valley, Africa. Abundances (in ppm) are: sanidine 0.45–0.61; fayalite 4.8–11.7; hedenbergite 5.1–9.0; titanomagnetite 2.7; ilmenite 0.48; amphibole 8.3–8.9; biotite 7.0; chevkinite-(Ce) 309; trachyte glass 3.0; rhyolitic glasses 2.3–3.9. These values are generally greater than those recorded for silicic rocks in the literature, whilst the chevkinite-(Ce) value is the largest yet found in a magmatic mineral. Apparent partition coefficients range from 0.15–0.26 in sanidine to 124 in chevkinite-(Ce). Those for fayalite and hedenbergite increase with whole-rock peralkalinity and Fe content. The possibility of a role for accessory phases in influencing Ge distribution in rock-forming minerals is also raised.

Keywords

peralkaline rhyolitesapparent partition coefficientssanidinefayalitehedenbergiteFeTi-oxidesamphibolebiotitechevkinite-(Ce)LA-ICP-MS.
Type
Research Article
Information
Mineralogical Magazine , Volume 71 , Issue 6 , December 2007 , pp. 703 - 713
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2007

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