A TEM study of disequilibrium plagioclase breakdown at high pressure; the role of infiltrating fluid

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Authors:Wayte, G. J.; Worden, R. H.; Rubie, D. C.; Droop, G. T. R.
Author Affiliations:Primary:
Univ. Manchester, Dep. Geol., GB-Manchester M13 9PL, United Kingdom
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 101(4), p.426-437. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1989
Note:In English. 34 refs.; illus. incl. 15 anal., 2 tables, geol. sketch map
Summary:High-P metamorphism in the Western Alps resulted in the breakdown of plagioclase (approx An65) to fine-grained zoisite, jadeite, kyanite and quartz. In rare cases this reaction failed to reach completion. The resulting textures of partial reaction have been studied by TEM and analytical EM. Incomplete reaction suggests that extent of reaction was controlled primarily by the availability of H2O. Two possible disequilibrium reaction models are proposed: 1) Plagioclase persists metastably with its original igneous composition to >17 kbar at 600 degrees C. Reaction then develops adjacent to cracks in response to the presence of aqueous fluid. At intra-crystalline sites only partial reaction occurs because jadeite, and sometimes kyanite and quartz, fail to nucleate for kinetic reasons. 2) Localized regions of a plagioclase crystal partially equilibrate at several stages during P increase, possibly due to discrete episodes of fluid infiltration. In both these models, the extent of reaction may be limited by NaSi-CaAl interdiffusion in plagioclase. [R.E.S.]
Subjects:Chain silicates; Clinopyroxene; Electron probe data; Epidote group; Feldspar group; Framework silicates; High pressure; Jadeite; Kyanite; Metamorphism; Nesosilicates; Orthosilicates; P-T conditions; Petrology; Phase transitions; Plagioclase; Pressure; Pyroxene group; Quartz; Silica minerals; Silicates; Sorosilicates; TEM data; Textures; Zoisite; Alps; Central Europe; Europe; Southern Swiss Alps; Swiss Alps; Switzerland; Allalin Gabbro; Reactions
Abstract Numbers:90M/1161
Record ID:1990007932
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe
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