The Composition of Anomalous Plagioclase Glass and Coexisting Plagioclase from Mistastin Lake, Labrador, Canada

K. L. Currie
Geological Survey of Canada, 601 Booth Street, Ottawa, Canada

Summary: Anorthosite country rocks near the fissure vents of an andesitic resurgent caldera contain coexisting crystalline plagioclase, pseudomorphous plagioclase glass, and anomalously dense, massive plagioclase glass. Glass pseudomorphous after labradorite (An 53) has the composition of oligoclase (An 17). Large masses of dense plagioclase glass have compositions near An 53, but relict crystalline plagioclase within them has compositions near An 80. Devitrification products of this glass have potassium-rich compositions. These compositions are compatible with partial thermal melting in a high-temperature, moderate-pressure pulse. Such a pulse might be asscciated with a confined chemical explosion.

Mineralogical Magazine; December 1971 v. 38; no. 296; p. 511-517; DOI: 10.1180/minmag.1971.038.296.14
© 1971, The Mineralogical Society
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