Petrographic, mineralogic, and chemical data obtained for dolerite dikes in the northwestern-most exposure of Precambrian rocks in the Bighorn Mountains indicate emplacement of tholeiitic magma during a single episode which postdates the time of recrystallization of the metasomatic, granitic country rock of the area. Modal, mineral-chemical, and rock-chemical variations across several of the dikes suggest that intradike differentiation followed the alkali-enrichment trend.

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