Hostname: page-component-586b7cd67f-l7hp2 Total loading time: 0 Render date: 2024-11-26T03:01:12.323Z Has data issue: false hasContentIssue false
  • English
  • Français

Conversion of nepheline to sodalite during subsolidus processes in alkaline rocks

Published online by Cambridge University Press:  05 July 2018

Adrian A. Finch
Adrian A. Finch*
Affiliation:
Department of Geology and Geophysics, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, U.K.
Get access Rights & Permissions [Opens in a new window]

Abstract

Cathodoluminescence (CL) petrography of nepheline syenites of the Igaliko complex, Gardar province, South Greenland shows that sodalites possess embayed contacts against nepheline, and have formed by a process of metasomatic replacement. This texture is demonstrated clearly by CL, since sodalite luminesces bright orange and nepheline is poorly luminescent. The transformation from nepheline to sodalite results in a volume change which leads to a network of fractures in which deep-blue luminescent fluorite is precipitated. Fluorite is formed since the chlorination process involved in the transformation causes localised reductions of the salinity of the fluid and therefore a decrease in the solubility of fluorite. Sodalite-fluorite textures observed using CL allow sodalites of secondary origin in alkaline igneous rocks to be identified.

Nephelines and sodalites, when observed using scanning electron microscopy, possess small micropores. By analogy with recent work on alkali feldspars, pervasive alteration of nephelines may occur by fluid flow assisted by a permeable micropore network.

Keywords

feldspathoidscathodoluminescencemicroporosityIgalikoGardarGreenlandalkaline rocks
Type
Research Article
Information
Mineralogical Magazine , Volume 55 , Issue 380 , September 1991 , pp. 459 - 463
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1991

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.)

Footnotes

*

Present address: Johnson Matthey Technology Centre, Blount's Court, Sonning Common, Reading RG4 9NH, U.K.

References

Barker, D. S. (1976) Phase Relations in the System NaAlSiO4-SiO2-NaCl-H2O at 400-800 °C and 1 kbar and Petrological Implications. J. Geol., 84, 97–1006.CrossRefGoogle Scholar
Beran, A. and Rossman, G. R. (1989) The Water Content of Nepheline. Mineral. Petrol., 40, 235-10.CrossRefGoogle Scholar
Blake, D. F., Allard, L. F., Echer, C. J., and Freund, F. (1988) Characterisation of Electron-beam Induced Damage Structures in Natural Fluorite, CaF2, by Analytical Electron Microscopy. In Microbeam Analysis (Newbury, D. E., ed.) San Francisco Press, San Francisco, 129-32.Google Scholar
Buerger, M. J., Klein, G. E., and Donnay, G. (1954) Determination of the Crystal Structure of Nepheline. Am. Mineral, 39, 805-18.Google Scholar
Deer, W. A., Howie, R. A., and Zussman, J. (1983) An introduction to the rock-forming minerals. Longmans, 528 pp.Google Scholar
Emeleus, C. H. and Harry, W. T. (1970) The Igaliko Nepheline Syenite Complex, Meddr. Gronland, 186, 115 pp.Google Scholar
Emeleus, C. H. and Upton, B. G. J. (1976) The Gardar Period in Southern Greenland. In The Geology of Greenland (Escher, A. and Watts, W. S., eds.) Gronlands Geol. Unders., Copenhagen, 152-81.Google Scholar
Finch, A. A. (1990) The Chemical and Isotopic nature of Fluids associated with Alkaline Magmatism, South Greenland. Unpubl. PhD thesis, University of Edinburgh, UK.Google Scholar
Finch, A. A. and Walker, F. D. L. (1991) Cathodoluminescence and microporosity in alkali feldspars from the Bla Måne Sø Perthosite, South Greenland. Mineral. Mag., 55 (in press).CrossRefGoogle Scholar
Geake, J. E., Walker, G., Telfer, D. J., and Mills, A. A. (1977) The Cause and Significance of Lumin-escence in Lunar Plagioclase. Phil. Trans. R. Soc. London, A285, 403–8.Google Scholar
Hassan, I. and Grundy, H. D. (1984) The Crystal Structures of Sodalite-group Minerals. Ada Cryst., B40, 6–13.Google Scholar
Hassib, A., Beckman, O., and Annersten, H. (1977) Photochromic Properties of Natural Sodalite. J. Phys. D(Appl. Phys.), 770–7.CrossRefGoogle Scholar
Lloyd, G. E. (1987) Atomic Number and Crystallo-graphic Contrast Images with the SEM: a Review of Backscattered Electron techniques. Mineral. Mag., 51, 3–19.CrossRefGoogle Scholar
Marshall, D. J. (1988) Cathodoluminescence of geologic materials. Unwin Hyman.Google Scholar
Powell, B. M. (1976) Theoretical, geochemical and petrological study of the Igdlerfigssalik nepheline syenite intrusion, Greenland. Unpubl. PhD thesis, University of Leeds, UK.Google Scholar
Rae, D. A. and Chambers, A. D. (1988) Metasomatism in the North Qoroq Centre, South Greenland: Cathodoluminescence and Mineral Chemistry of Alkali Feldspars. Trans. R. Soc. Edin.: Earth Sci., 79, 1–12.Google Scholar
Richardson, C. K. and Holland, H. D. (1979) The Solubility of Fluorite in Hydrothermal Solutions, an Experimental Study. Geochim. Cosmochim. Ada, 43, 1313-25.CrossRefGoogle Scholar
Schipper, D. J., van Doom, C. Z., and Bolwijn, P. T. (1972) Preparation of Cathodochromic Sodalites. J. Am. Ceram. Soc, 55, 256–9.CrossRefGoogle Scholar
Sharp, Z. D., Helffrich, G. R., Bohlen, S. R., and Essene, E. J. (1989) The Stability of Sodalite in the System NaAlSiO4-NaCl. Geochim. Cosmochim. Ada, 53, 1943-54.CrossRefGoogle Scholar
Upton, B. G. J. and Emeleus, C. H. (1987) Mid-Proterozoic Alkaline Magmatism in Southern Greenland: the Gardar Province. In Alkaline Igneous Rocks (Fitton, J. G. and Upton, B. G. J., eds.) Spec. Publ. Geol. Soc. London, 30, 449-71.Google Scholar
Walker, F. D. L. (1990) Ion Microprobe Study of Intragrain Micropermeability in Alkali Feldspars. Contrib. Mineral. Petrol, 106, 124–8.Google Scholar
Worden, R. H., Walker, F. D. L., Parsons, I., and Brown, W. L. (1990) Development of Microporosity, Diffusion Channels and Deuteric Coarsening in Perthitic Alkali Feldspars. Ibid. 104, 507-15.Google Scholar