Abstract

Uranium–lead dates for nine zircon fractions from six rock samples of Central Gneiss complex (CGC) are concordant between 65 and 85 Ma. Two fractions from a sample near the eastern edge of the CGC give discordant U–Pb dates between 108 and 171 Ma, but analytical uncertainties and geological complexities prohibit meaningful interpretation. Two fractions from two samples from the Ecstall pluton give concordant U–Pb dates of about 98 ± 4 Ma and date the emplacement of the Ecstall pluton. The concordant CGC dates indicate Late Cretaceous to early Tertiary peak metamorphism (granulite and amphibolite facies) of the CGC east of Work Channel lineament. This contrasts with a slightly older (mid-Cretaceous) peak metamorphism west of Work Channel lineament inferred from the synmetamorphic nature of the Ecstall pluton.

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