An isotopic study of the Island Lake Greenstone Belt, Manitoba: crustal evolution and progressive cratonization in the late Archean

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Abstract
Three new U–Pb zircon ages are reported for units within the Island Lake Greenstone Belt in northern Manitoba: the Jubilee Island dacite (2761 ± 12 Ma), the Chapin Bay tonalite (2748 ± 3 Ma), and the Wassagomach tonalité (2778 ± 5 Ma). Rb–Sr data suggest a mild metamorphic event about 2736 ± 67 Ma ago. Basalts within the basal Hayes River Group (2860–2900 Ma) appear to be derived from a time-averaged, Nd-depleted mantle with εNd values between +0.78 and +2.1. Lower εNd values (< +0.31) are found in volcanic and intrusive rocks of the same age, implying contamination by or remelting of preexisting crust to form the more felsic derivatives. εNd values of early tonalitic, trondhjemitic, and granitic plutons (2729–2900 Ma) decrease from +0.31 to −1.8 as the plutons become younger, and are indicative of a period of dominantly intracrustal recycling processes in the Island Lake region. It is suggested that this trend records the evolution of the Island Lake region through extensive intracrustal melting and recycling from a variably contaminated volcanic arc to a small mature craton. Uplift associated with the plutonism resulted in sedimentation of the Island Lake Group (2729–2749 Ma), followed by renewed granitic plutonism of the Late Intrusive Suite (2699–2729 Ma). εNd values of these units range from +3 to −3, suggesting renewed interaction of depleted mantle with the Island Lake crust. This possibly resulted from magmatism associated with the accretion of the Island Lake Terrane to the rest of the Superior Province.

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