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Synneusis of zircon: why not?

Published online by Cambridge University Press:  05 July 2018

P. Alexandrov
P. Alexandrov*
Affiliation:
CRPG-CNRS, BP 20, 54501 Vandú uvre CEDEX, France
*
*E-mail: [email protected]
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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).

Keywords

synneusiszirconSoultz graniteHercynianFrance
Type
Research Article
Information
Mineralogical Magazine , Volume 65 , Issue 1 , February 2001 , pp. 71 - 79
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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Footnotes

†

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

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