Study of the texture of mica flakes in microflexures associated with crenulation cleavage suggested criteria for estimating the extent of mica recrystallization. These criteria were applied to a sample case, the dating of cleavage-plane micas from folds developed during two deformation episodes in the Canadian Appalachians. The validity of the method, however, was not adequately tested because the micas from early and late cleavage planes gave the same K-Ar age, but the results permitted the interesting conclusion that the Taconic orogeny probably occurred in three distinct phases of markedly contrasting structural styles.

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