Hostname: page-component-586b7cd67f-vdxz6 Total loading time: 0 Render date: 2024-11-23T03:35:25.738Z Has data issue: false hasContentIssue false

Synneusis of zircon: why not?

Published online by Cambridge University Press:  05 July 2018

P. Alexandrov*
Affiliation:
CRPG-CNRS, BP 20, 54501 Vandú uvre CEDEX, France
*

Abstract

Some zircons from the Hercynian Soultz granite, NE France, exhibit complex structures, with double cores and oscillatory-banded overgrowths. These glomeroporphyritic crystals are uncommon for zircons, in which synneusis has not previously been described. The cores of the zircons are considered to correspond to very quickly formed {100} or {110} prisms. These could slowly sediment in the magma chamber and cluster together while sinking. The overgrowth rims correspond to a slower growth rate.

U/Pb ion-probe dating of the cores and the overgrowth rims provided the same age of 327±6 Ma. Chemical electron microprobe analyses indicated that cores and rims have the same composition for major and trace elements.

The sinking of zircons accounts for the abnormally high percentages of zircon in the lower parts of the granite. The formation of clusters in the early stages of crystallization needs stable P/T conditions, a hot, liquid silicate melt with a high fluid content, and no other minerals crystallizing (liquidus phase).

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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: Department of Geological Sciences, Miller Hall, Queen's University, Kingston, Ontario, Canada K7L 3N6

References

Alexandrov, P., Cheilletz, A., Deloule, E. and Cuney, M. (2000) 319 ± 7 Ma crystallisation age for the Blond granite (Northwest Limousin, French Massif Central) obtained by U-Pb ion-probe dating of zircons. C. R. Acad. Sci. Paris, 330, 17.Google Scholar
Allaby, A. and Allaby, M., editors (1990) The Concise Oxford Dictionary of Earth Sciences. Oxford University Press, Oxford.Google Scholar
Dowty, E. (1980) Synneusis reconsidered. Contrib. Mineral. Petrol., 74, 7584.CrossRefGoogle Scholar
Genter, A., Homeier, G., Chèvremont, Ph. and Tenzer, H. (1999) Deepening of GPK-2 HDR borehole, 3880–5090 m (Soulz-sous-Forêts, France ). Geological monitoring, Rapport BRGM R 40685, 44 pp.Google Scholar
Hanchar, J.M. and Miller, C.F. (1993) Zircon zonation patterns as revealed by cathodoluminescence and backscattered electron images: Implications for interpretation of complex crustal histories. Chem. Geol., 110, 113.CrossRefGoogle Scholar
Pupin, J.P. (1980) Zircon and granite petrology. Contrib. Mineral. Petrol., 73, 207–20.CrossRefGoogle Scholar
Pupin, J.P. and Turco, G. (1972) Application des données du zircon accessoire en pétrologie endogène (Application of accessory zircon data in endogenous petrology). C. R. Acad. Sci. Paris, 275, 799801.Google Scholar
Schwindinger, K.R. and Anderson, A.T. Jr, (1989) Synneusis of Kilauea Iki olivines. Contrib. Mineral. Petrol., 103, 187–98.CrossRefGoogle Scholar
Schwindinger, K. (1999) Particle dynamics and aggregation of crystals in a magma chamber with application to Kilauea Iki olivines. J. Volcanol. Geotherm. Res., 88, 209–38.CrossRefGoogle Scholar
Smith, M.P., Savary, V., Yardley, B.W.D., Valley, J.W., Royer, J.J. and Dubois, M. (1998) The evolution of the deep flow regime at Soulz-sous-Forêts, Rhine Graben, eastern France: Evidence from a composite quartz vein. J. Geophys. Res., 103, 27,223–37.Google Scholar
Speer, J.A. (1980) Zircon. Ortho-silicates. Mineralogical Society of America, Washington, D.C. Google Scholar
Traineau, H., Genter, A., Cautru, J.P., Fabrion, H. and Chèvremont, P. (1991) Petrography of the granite massif from drill cutting analysis and well log interpretation in the geothermal HDR borehole GPK1 (Soultz, Alsace, France). Geoth. Sci. Tech., 3, 129.Google Scholar
Vance, J.A. (1969) On synneusis. Contrib. Mineral. Petrol., 24, 729.CrossRefGoogle Scholar
Vavra, G. (1994) Systematics of internal zircon morphology in major Variscan granitoid type. Contrib. Mineral. Petrol., 117, 331–44.CrossRefGoogle Scholar