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The evolution of fluorine-rich felsic magmas: source dichotomy, magmatic convergence and the origins of topaz granite

Taylor, R.P., and Fallick, A.E. (1997) The evolution of fluorine-rich felsic magmas: source dichotomy, magmatic convergence and the origins of topaz granite. Terra Nova, 9 (3). pp. 105-108. ISSN 0954-4879

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Publisher's URL: http://www3.interscience.wiley.com/journal/119175627/abstract

Abstract

Topaz granite is alkali-feldspar granite that contains essential albite, quartz, K-feldspar, lithium-mica, and topaz. As a group topaz granites are characterized by their extreme enrichment in F (up to 3 wt%) and a wide variety of lithophile elements. They can be subdivided into a 'low-P2O5 subtype' (P2O5 < 0.1 wt%, Al2O3 < 14.5 wt%, SiO2 > 73 wt%) and a 'high-P2O5 subtype' (P2O5 > 0.4 wt%, Al2O3 > 14.5 wt%, SiO2 < 73 wt%), the δ18O values of which indicate a dichotomy of source rock: the low-P2O5 subtype (δ18O < 10‰) having a meta-igneous protolith and the high-P2O5 subtype (δ18O > 10‰) a source with a significant component of pelitic material. The unusually high F contents enhance the efficacy of melt segregation and crystal-melt fractionation and so facilitate extreme differentiation in topaz granite magmas. Very low melt volumes restrict the bulk composition of the partial melts regardless of the nature of the source; and extreme fractionation forces them along a path of magmatic convergence, to produce a group of granitic rocks with near-minimum compositions so enriched in a variety of lithophile elements (Li, Nb, Ta, Sn) that economic mineralization often results.

Item Type:Article
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Fallick, Prof Anthony
Authors: Taylor, R.P., and Fallick, A.E.
Subjects:Q Science > QE Geology
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Terra Nova
Publisher:Wiley-Blackwell Publishing Ltd.
ISSN:0954-4879
ISSN (Online):1365-3121
Published Online:25 November 2003

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