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Kinetics of pyrope megacryst reactions in ascending basaltic magma – relevance to high-pressure magmatic crystallization at Elie Ness, East Fife

Published online by Cambridge University Press:  01 May 2009

Colin H. Donaldson
Colin H. Donaldson
Affiliation:
Department of Geology, University of St Andrews, St Andrews, Fife KYI6 9ST, Scotland
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Abstract

The rates of resorption of pyrope in basaltic melt and of pyrope decomposition to pyroxene + melt at pressures below the stability of garnet are used to examine the proposition (Chapman, 1976) that pyrope megacrysts in the Elie Ness neck began ascent from the mantle at 1300–1450°C. Both reactions are extremely rapid at these temperatures and yet the petrographic evidence is that neither occurred. Either the transporting magma cooled extremely rapidly during ascent (> 30000 °/h) or, more likely, was considerably cooler than previously proposed. Water was a significant constituent of the magma, and a crystallization temperature for the garnet of as little as 1000 °C is possible, based on existing phase–equilibria data.

Type
Articles
Information
Geological Magazine , Volume 121 , Issue 6 , November 1984 , pp. 615 - 620
Copyright
Copyright © Cambridge University Press 1984

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