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A chemical study of the ignimbrites of Arisaig, Nova Scotia, was undertaken to determine their geochemical character, any variations within flow units, and their relationship to associated volcanics.

The ignimbrites are rhyolitic in composition and there seems to be no primary chemical variation within individual flow units. The area has been subjected to low-grade regional metamorphism, probably to greenschist facies, which accounts for most of the variation within each ignimbrite.

The rock type previously called "andesite" is found to be more appropriately classified as a spilite.

Some possible indicators of the nature of the rock suite are investigated, including trace- and rare-earth element distributions, and possible interpretations of the origin of this bimodal occurrence are discussed.

The chemical evidence favours a model involving fractional crystallization.

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Pages: 92
Supervisor:听 D. B. Clarke

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