Truth and beauty in metamorphic phase equilibria; conjugate variables and phase diagrams

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doi: 10.2113/gscanmin.43.1.21
Authors:Powell, Roger; Guiraud, Michel; White, Richard W.
Author Affiliations:Primary:
University of Melbourne, School of Earth Sciences, Parkville, Victoria, Australia
Other:
Geological Survey of Canada, Canada
Talisman Energy, Canada
Muséum National d'Hitsoire Naturelle, France
Volume Title:Truth and beauty in metamorphism; a tribute to Dugald Carmichael
Volume Authors:Pattison, David R. M.; St-Onge, Mark R.; Bégin, Normand J.
Source:Truth and beauty in metamorphism; a tribute to Dugald Carmichael, David R. M. Pattison, Mark R. St-Onge and Normand J. Bégin. The Canadian Mineralogist, Vol.43(Part 1), p.21-33. Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada. ISSN: 0008-4476
Publication Date:2005
Note:In English with French summary. 18 refs.; illus.
Summary:In using calculated equilibria among minerals to understand metamorphic processes, there are usually "natural" choices of axes to use on phase diagrams, depending on the geological supposition of the processes operating in rocks. Thermodynamic variables come in conjugate pairs, intensive and extensive, and the natural choice of which to use as an axis of a phase diagram depends on which of the pair leads to paths for metamorphic processes that are easiest to visualize. An unnatural choice leads to diagrams on which paths are not intuitively obvious, and these diagrams usually have to be calculated. Ideas relating to conjugate pairs are illustrated using mineral equilibria for the upper amphibolite to granulite facies, calculated for an aluminous pelite composition in the system Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O (NCKFMASH). We look specifically at the pressure-volume conjugate pair and the H2O content-aH2O pair (i.e., the H2O-µH2O pair). P-T versus V-T and T-MH2O versus T-aH2O diagrams are used to consider metamorphic processes. We show that the less obvious variable, for example V rather than P, may be more useful in considering certain situations, usually transient.
Sections:Experimental mineralogy
Subsections:General; Metamorphic rocks
Subjects:Amphibolite facies; Chemical composition; Chemical reactions; Facies; Granulite facies; High-grade metamorphism; Metamorphic rocks; Metamorphism; Mineral assemblages; Mineral composition; P-T conditions; Partial melting; Phase equilibria; Silicates; Temperature; Thermodynamic properties; Volume; Water; Water-rock interaction
Abstract Numbers:05M/1716
Record ID:2006008901
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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