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Exsolution of plagioclase from clinopyroxene in a pyroxenite from Jotunheimen, Norway

Published online by Cambridge University Press:  05 July 2018

M. H. Battey  and
W. Davidson
M. H. Battey
Affiliation:
Geology Department, University of Newcastle upon Tyne
W. Davidson
Affiliation:
School of Physics, University of Newcastle upon Tyne
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Summary

Petrography of an original websterite from Jotunheimen shows evidence of plagioclase exsolving from clinopyroxene to form both internal lamellae and also an intergranular symplectite with olivine and magnetite hercynite. The olivine is secondary, forming from both clinopyroxene and orthopyroxene. Microprobe chemical analyses are presented of all the phases mentioned. From the ratio of plagioclase to clinopyroxene the initial clinopyroxene probably formed at a depth greater than 35 km; if it crystallized at magmatic temperatures (1150°C) the depth must have been about 70 km. Exsolution took place at a pressure less than 6 kb after upthrusting of the rock to shallower depths. The great depth of initial crystallization has important implications for the conditions of origin of the ultramafic component of this granulite facies terrain.

Type
Research Article
Information
Mineralogical Magazine , Volume 41 , Issue 320 , December 1977 , pp. 513 - 518
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1977

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