Hostname: page-component-cd9895bd7-fscjk Total loading time: 0 Render date: 2024-12-25T19:13:59.203Z Has data issue: false hasContentIssue false
  • English
  • Français

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]
Get access Rights & Permissions [Opens in a new window]

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

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Bailey, J.C. (2001) Distributionof germanium inrocks and minerals of the Ilímaussaq alkaline complex, South Greenland. Geology of Greenland Survey Bulletin, 190, 55–64.Google Scholar
Bernstein, L.R. (1985) Germanium geochemistry and mineralogy. Geochimica et Cosmochimica Acta, 49, 2409–2422.CrossRefGoogle Scholar
Black, S., Macdonald, R. and Kelly, M.R. (1997) Crustal originfo r peralkaline rhyolites from Kenya: Evidence from U–series disequilibria and Thisotopes. Journal of Petrology, 38, 277–297.CrossRefGoogle Scholar
Capobianco, C.J. and Watson, E.B. (1982) Olivine/ silicate melt partitioning of germanium: an example of a nearly constant partition coefficient. Geochimica et Cosmochimica Acta, 46, 235–240.CrossRefGoogle Scholar
Clarke, M.C.G., Woodhall, D.G., Allen, D. and Darling, G. (1990) Geological, volcanological and hydrogeological controls on the occurrence of geothermal activity in the area surrounding Lake Naivasha, Kenya. Ministry of Energy Report, Nairobi.Google Scholar
Ewart, A. and Griffin, W.I. (1994) Application of proton–microprobe data to trace–element partitioning involcan ic rocks. Chemical Geology, 117, 251–284.CrossRefGoogle Scholar
Harris, P.G. (1954) The distributionof germanium among coexisting phases of partly glassy rocks. Geochimica et Cosmochimica Acta, 5, 185–195.CrossRefGoogle Scholar
Heumann, A. and Davies, G.R. (2002) U–Th disequilibrium and Rb–Sr age constraints on the magmatic evolutionof peralkaline rhyolites from Kenya. Journal of Petrology, 43, 557–577.CrossRefGoogle Scholar
Hörmann, P.K. (1963) Zur Geochemie des Germaniums. Geochimica et Cosmochimica Acta, 27, 861–876.CrossRefGoogle Scholar
Li, G., Yang, G., Ma, Z., Shi, N., Xiong, M., Fan, H. and Sheng, G. (2005) Crystal structure of natural nonmetamict Ti– and Fe2+–rich chevkinite–(Ce). Acta Geologica Sinica, 79, 325–331.Google Scholar
Macdonald, R. and Bailey, D.K. (1973) The chemistry of the peralkaline oversaturated obsidians. U.S. Geological Survey Professional Paper, 440–N–1, N1–N37.Google Scholar
Macdonald, R., Davies, G.R., Bliss, C.M., Leat, P.T., Bailey, D.K. and Smith, R.L. (1987) Geochemistry of high–silica peralkaline rhyolites, Naivasha, Kenya Rift Valley. Journal of Petrology, 28, 979–1008.CrossRefGoogle Scholar
Macdonald, R., Marshall, A.S., Dawson, J.B., Hinton, R.W. and Hill, P.G. (2002) Chevkinite–group minerals from salic volcanic rocks of the East AfricanRift. Mineralogical Magazine, 66, 287–299.CrossRefGoogle Scholar
Marshall, A.S., Hinton, R.W. and Macdonald, R. (1998) Phenocrystic fluorite in peralkaline rhyolites, Olkaria, Kenya Rift Valley. Mineralogical Magazine, 62, 477–486.CrossRefGoogle Scholar
Miyawaki, R., Matsubara, S. and Miyajima, H. (2002) The crystal structure of rengeite, Sr4ZrTi4(Si2O7)2O8 . Journal of Mineralogical and Petrological Sciences, 97, 7–12.CrossRefGoogle Scholar
Pearce, N.J.G., Westgate, J.A., Perkins, W.T. and Preece, S.J. (2004) The applicationof ICP–MS methods to tephrochronological problems. Applied Geochemistry, 19, 289–322.CrossRefGoogle Scholar
Pouchou, J.L. and Pichoir, F. (1985) "PAP" procedure for improved quantitative analysis. Microbeam Analysis, 20, 104–105.Google Scholar
Scaillet, B. and Macdonald, R. (2001) Phase relations of peralkaline silicic magmas and petrogenetic implications. Journal of Petrology, 42, 825–845.CrossRefGoogle Scholar
White, J.C. (2003) Trace–element partitioning between alkali feldspar and peralkalic quartz trachyte to rhyolite magma. Part II: Empirical equations for calculating trace–element partition coefficients of large–ion lithophile, high field–strength, and rareearth elements. American Mineralogist, 88, 330–337.Google Scholar
White, J.C., Holt, G.S., Parker, D.F. and Ren, M. (2003) Trace–element partitioning between alkali feldspar and peralkalic quartz trachyte to rhyolite magma: Part I: Systematics of trace–element partitioning. American Mineralogist, 88, 316–329.Google Scholar