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The petrography and geochemistry of corona-bearing dolerites from the Jotun Nappe, central southern Norway

Published online by Cambridge University Press:  05 July 2018

T. F. Emmett
T. F. Emmett*
Affiliation:
Department of Geology, The University, Keele, Staffs., ST5 5BG, England
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Abstract

The petrography and geochemistry of a suite of dolerite dykes emplaced into orthogneisses of the Jotun Nappe, central southern Norway, are described. The dolerites, which appear to be tholeiitic in character, show well-developed ophitic and doleritic textures and are not foliated. They contain corona structures of six types which represent the various stages of reaction between olivine or clinopyroxene and plagioclase, and oxide grains and plagioclase. Corona growth always proceeds after the plagioclase has become clouded with numerous extremely fine opaque particles, and reaches its fullest development in rocks with the most heavily clouded plagioclase. Garnet grows in coronas only in rocks with Fe2O3/(Fe2O3 + FeO) = 0.20 to 0.27. The ratio MgO/MgO + Fe2O3 + FeO) is of lesser importance in controlling the growth of this mineral. The role of water in coronaforming reactions, and the preservation of original igneous textures indicates that the coronas are a product of post-solidification deuterism, possibly active at high pressures and temperatures, rather than of prograde metamorphism.

Type
Research Article
Information
Mineralogical Magazine , Volume 46 , Issue 338 , March 1982 , pp. 43 - 48
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1982

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Footnotes

*

Present address: Department of Science (Geology), Cambridgeshire College of Art and Technology, Cambridge, CB1 2AJ.

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