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Co-existing Pyroxenes in Igneous Assemblages: a Re-evaluation of the Existing Data on Tie-line Orientations

Published online by Cambridge University Press:  01 May 2009

G. M. Brown
G. M. Brown
Affiliation:
Department of Geology and Mineralogy, University Museum, Oxford.
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Abstract

Tie-line data are presented for twelve analysed igneous pyroxene pairs, from which it is demonstrated that a precise point of intersection, at or close to Wo75 En25 in the ternary diagram, does not exist. Eight tie-lines for pyroxene pairs from ultrabasic nodules in basalts are also considered. The tie-lines for metamorphic pyroxenes are compared with the igneous, and are shown to intersect over a similarly wide range, the average (Ca82 Mg18) being the same for both assemblages. It is shown that no conclusions can be drawn as to the genesis of the pyroxene assemblage, from the assumption of a characteristic tie-line intersection point. Optical determinations are considered, and shown to be of little practical value in this particular problem.

Type
Articles
Information
Geological Magazine , Volume 98 , Issue 4 , August 1961 , pp. 333 - 343
Copyright
Copyright © Cambridge University Press 1961

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References

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