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Equilibria in the Mg-rich part of the pyroxene quadrilateral

Published online by Cambridge University Press:  05 July 2018

G. A. Jenner
Affiliation:
Department of Geology, University of Tasmania, Hobart, Tasmania, Australia 7001
D. H. Green
Affiliation:
Department of Geology, University of Tasmania, Hobart, Tasmania, Australia 7001

Abstract

Pyroxene phase relations in the Mg-rich corner of the pyroxene quadrilateral, at 1 atmosphere, have been reinvestigated. Experimental studies on sixteen selected compositions in the systems CMS and CFMS were undertaken in the temperature range 1100–1400 °C. The results of this study clarify our understanding of the pyroxene stability relations at low pressure. In particular, the demonstration that there is a high-temperature stability field of orthoenstatite denies the existence of a stable (or real) invariant point defined by the reactions OE = PE + DI, PE + DI = PI, and OE + DI = PI, in the system CaMgSi2O6-Mg2Si2O6. New phase relations, consistent with the experimental findings of this and other studies, for the Mg-rich corner of the pyroxene quadrilateral are presented. These new phase relations may be of use in interpreting the origin of volcanic rocks containing magnesian pigeonite.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1983

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Footnotes

*

Present address: Max-Planck Institut für Chemie, Saarstrasse 23, Postfach 3060, D-6500 Mainz, West Germany.

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