Abstract

Sm–Nd isotopic data from five mafic intrusions in the La Ronge – Lynn Lake Domain indicate crystallization between 1.88 and 1.79 Ga. The data from a single intrusion in the Glennie Lake Domain suggest a slightly younger age of about 1.71 Ga. These results indicate a cogenetic origin of the mafic intrusions with the associated volcanic and plutonic rocks.Initial εNd values vary from +4.5 to −0.6 and can be modeled by mixing Proterozoic mantle-derived magmas with ≤17% Archaean crust or subduction of ≤3% sediment similar to pelites from the Wollaston Domain. The initial εNd value of 0 for a Late Proterozoic Mackenzie dike is compatible with an origin from mantle sources affected by Hudsonian subduction processes.Rb–Sr data indicate variable and generally high initial 87Sr/86Sr isotopic ratios, which reflect, in part, isotopic redistribution during metamorphism. δ18O values of coexisting clinopyroxene, orthopyroxene, and plagioclase indicate isotopic disequilibrium. Plagioclase samples show variable degrees of enrichment in 18O due to isotopic exchange with metamorphic fluids that probably also affected Rb and Sr.

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