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The geochemistry of Archaean plagioclase-rich granites as a marker of source enrichment and depth of melting

By
J.-F. Moyen
J.-F. Moyen
Department of Geology, Geography and Environmental Studies, University of Stellenbosch, PVT Bag X1, 7602 Matieland, South Africa, Email: moyen@sun.ac.za, Current address: Département de Géologie, Université Jean-Monnet & CNRS 23, rue du Docteur Michelon, 42023 Saint-Etienne cedex, France, Email: jean.francois.moyen@univ-st-etienne.fr
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D. Champion
D. Champion
Geoscience Australia, Canberra, Australia, Email: David.Champion@ga.gov.au
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R. H. Smithies
R. H. Smithies
GSWA, Perth, W. Australia, Email: hugh.smithies@dmp.wa.gov.au
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Published:
October 01, 2010

In geochemical diagrams, granitoids define ‘trends’ that reflect increasing differentiation or melting degree. The position of an individual sample in such a trend, whilst linked to the temperature of equilibration, is difficult to interpret. On the other hand, the positions of the trends within the geochemical space (and not the position of a sample within a trend) carry important genetic information, as they reflect the nature of the source (degree of enrichment) and the depth of melting. This paper discusses the interpretation of geochemical trends, to extract information relating to the sources of granitoid magmas and the depth of melting.

Applying this approach to mid-Archaean granitoids from both the Barberton granite–greenstone terrane (South Africa) and the Pilbara Craton (Australia) reveals two features. The first is the diversity of the group generally referred to as ‘TTGs’ (tonalites, trondhjemites and granodiorites). These appear to be composed of at least three distinct sub-series, one resulting from deep melting of relatively depleted sources, the second from shallower melting of depleted sources, and the third from shallow melting of enriched sources. The second feature is the contrast between the (spatial as well as temporal) distributions and associations of the granites in both cratons.

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GSA Special Papers

Sixth Hutton Symposium on The Origin of Granites and Related Rocks: Proceedings of a Symposium held in Stellenbosch, South Africa, 2- 6 July 2007

John D. Clemens
John D. Clemens
Department of Earth Sciences, University of Stellenbosch, South Africa
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Colin Donaldson
Colin Donaldson
EESTRSE Editor:
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Carol D. Frost
Carol D. Frost
Guest Editors:
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Alexander F.M. Kisters
Alexander F.M. Kisters
Guest Editors:
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Jean-François Moyen
Jean-François Moyen
Guest Editors:
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Tracy Rushmer
Tracy Rushmer
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Gary Stevens
Gary Stevens
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Geological Society of America
Volume
472
ISBN print:
9780813724720
Publication date:
October 01, 2010

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