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Metamorphic Grade and Iron-Magnesium Distribution between Co-Existing Garnet-Biotite and Garnet-Hornblende

Published online by Cambridge University Press:  01 May 2009

M. J. Frost
Affiliation:
Department of Geology, University of Canterbury, Christchurch, N.Z.

Abstract

It is shown that in the two mineral pairs discussed the metamorphic grade can be estimated from the atomic ratios (Xa = Mg/Mg + Fe + 0·175 Mn + 0·360 Ca) in garnet and Xb = Mg/(Mg + Fe) in the other mineral. The standard error of the estimation is about one-third of the temperature range of the amphibolite facies.

Where M is the metamorphic grade on an arbitrary scale, in which the lower boundary of the amphibolite facies is at 4·2 and the upper at 5·1, and K is the distribution coefficient (XbXaXb)/(XaXaXb), then the estimating equation is M = 5·6 — 1·5 log10 K.

Type
Articles
Copyright
Copyright © Cambridge University Press 1962

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