Abstract

The contamination of small intrusive bodies of alkali-syenite by xenoliths of nepheline-bearing gneiss of the surrounding country rocks has produced two types of hybrid rocks. In one, the contaminant was nepheline-bearing gneiss which led to the formation of nepheline-syenite; in the other, the contaminant was probably nepheline-free gneiss which resulted in the formation of saturated aegirine-syenite. Only one locality of the hybrid nepheline-syenite has been found, and therefore this type of contamination is probably not responsible for producing large volumes of undersaturated magma. Four new rock analyses are presented.

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