Isotopic analysis of five large books of muscovite from a pegmatite emplaced between the third and fourth deformational phases of the Svecokarelian orogenic episode indicate crystallization before 1880 m.y. with regional temperatures remaining elevated for about 120 m.y.The data are used to assess the validity of correlating deformational phases on the basis of structural evidence.
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BREEMEN et al. (1977) studied this question.