Abstract

Two cross-cutting mafic dikes in the headwall of Gardner Lake in the eastern Beartooth Mountains, Wyoming, have structural relations with Archean migmatite and gneiss that suggest intrusion between deformational phases recognized in the eastern part of the range. Fabric data show that the older dike, an orthoamphibolite, was emplaced subsequent to the F1 deformational event, but prior to the main episode of metamorphism, metasomatism, and folding, F2. The younger dike, a metanorite, was intruded after F2, but is folded by west-trending, open F3 folds. The style and general trend of these F3 folds are consistent with those observed elsewhere in the eastern part of the range. The data available and absolute age relations in other parts of the range indicate that F2 occurred 2750 m.y. ago and F3 1600 to 1800 m.y. ago.

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