U-Pb isotopic analyses of three cogenetic zircon fractions from a Precambrian rhyolite of the Quinnesec Formation in northeastern Wisconsin yielded a concordia intercept age of 1905 (+30 to −10) m.y. Thus, at least part of the Quinnesec Formation is late or post-Animikie in age and is not correlative with the pre-Animikie complexes of Michigan, as has been previously believed.

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