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The influence of secondary alteration on the ammonium content of granites, exemplified by the Rosses complex of Donegal

Published online by Cambridge University Press:  05 July 2018

A. Hall
A. Hall*
Affiliation:
Department of Geology, Royal Holloway College, Egham, Surrey TW20 0EX
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Abstract

Ammonium analyses of representative rocks from the Rosses granite complex (Ireland) and their constituent mineral show that any variation of magmatic origin has been completely obscured by pervasive hydrothermal alteration. The altered rocks are strongly enriched in the ammonium ion, most of which is held by chloritized biotite and sericitized plagioclase. The present ammonium content of the Rosses granites averages 13 ppm, but the original ammonium content of the magmas is estimated to have been less than 5 ppm. Potassium feldspars may preserve a better record of the original magmatic ammonium content than the whole rocks or the biotites.

Keywords

ammoniumRosses complexIrelandgranitesecondary alteration
Type
Geochemistry and Petrology
Information
Mineralogical Magazine , Volume 57 , Issue 389 , December 1993 , pp. 591 - 598
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1993

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