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Understanding Pegmatite Formation: The Melt And Fluid Inclusion Approach


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Thomas, R, Webster, JD and Davidson, P 2006 , 'Understanding Pegmatite Formation: The Melt And Fluid Inclusion Approach', in James, D. Webster (ed.), Melt Inclusions in Plutonic Rocks , Short Course Series (36) , Mineralogical Association of Canada, Montreal, Quebec, pp. 189-210.

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Despite extensive studies on pegmatites in the past (Barth 1928, Bjorlykke 1935, Brotzen 1959, Niggli 1920, 1937) and more recently (Cerny 1982, Gordienko 1996, London 2005, Peretyazhko et al., 2004 Shmakin & Makagkon 1999, Strunz 1974) their origin and genesis remain controversial, particularly so for complexly zoned pegmatites. Some researchers (e.g., Fersmann 1931, Turner & Verhoogen 1960) consider them to be of igneous origin, while others believe that pegmatites are metamorphically or metasomatically generated (e.g., Barth 1962, Gresens 1967). In this paper we present evidence in favor of the igneous origin of pegmatites and provide insights into some major pegmatite-forming processes. Our evidence is based primarily on fluid and melt inclusions (FI and MI, respectively) and experimental studies, and suggests that the vast majority of granitic pegmatites are of magmatic origin, even though many may be affected by recrystallization and metasomatism. The very existence of silicate melt inclusions in minerals of pegmatites provides proof of their magmatic origin. In this contribution, we also discuss melt and fluid inclusion evidence concerning the nature and evolution of some granitic pegmatites. Our observations bear primarily on F-enriched and/or alkaline pegmatites, but they are also useful for considering processes involving simple pegmatites composed of feldspar, quartz, and little else. We confine ourselves to major processes of pegmatite formation that can be constrained by the study of MI and FI. Processes and evidence of the late hydrothermal evolution stage, characterized by dilute aqueous solutions, are beyond the scope of this paper.

Item Type: Book Section
Authors/Creators:Thomas, R and Webster, JD and Davidson, P
Keywords: Pegmatite, pegmatite formation, melt inclusions, fluid inclusions
Publisher: Mineralogical Association of Canada
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