Exsolution of Plagioclase from Clinopyroxene in a Pyroxenite from Jotunheimen, Norway

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

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.

Mineralogical Magazine; December 1977 v. 41; no. 320; p. 513-518; DOI: 10.1180/minmag.1977.041.320.13
© 1977, The Mineralogical Society
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