Abstract

The U–Pb zircon age for the Chibougamau pluton is some 200 Ma older than the published Rb–Sr total-rock age. However, application of sample rejection techniques based on petrography, volatile content, and major-element chemistry to published and new Rb–Sr data, permits a selection of less altered total-rock samples which define an age in close agreement with the zircon age. These data suggest that the Chibougamau pluton crystallized with a uniform initial-Sr ratio equivalent to values for the surrounding metavolcanics and by inference Earth's mantle at 2.7 Ga.

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