Abstract

Hudsonian tectonism in the western Churchill Province of Canada encompassed two periods of granitic plutonism. The Hudson suite plutons represent xenocryst-rich, mainly monzogranitic, near-minimum melts emplaced near their source region in thickened middle crust; the Nueltin syenogranites and Pitz rhyolites were generated by intrusion of basalt into extending crust. Zircons from four Nueltin suite samples and 20 Hudson suite samples were analysed by U–Pb SHRIMP techniques. Intrusion of the Hudson suite lasted ca. 50 million years, from 1845 to 1795 Ma, with a peak around 1825 Ma, and the Nueltin suite from 1765 to 1750 Ma, following a ca. 30-million-year period of magmatic quiescence. A marked contrast in Th/U ratios was found in igneous zircon from Hudson suite samples south (Th/U = 0.066) and north (Th/U = 1.07) of the northern margin of the Central Hearne domain and is attributed to a difference in the nature of the melting process, with the lower values representing ultrametamorphism and the higher values representing bulk melting resulting from contact with mafic igneous magma. Whole-rock Nd isotopic measurements, with average ε143Nd near –10, indicate a dominant late Archean crustal component in both suites of granites, reflected by numerous inherited zircon ages between 2720 and 2650 Ma in Hudson granites. Further south, along the Manitoba border, inherited zircons of 3500–3000 Ma, together with previously published U–Pb data on gneisses and ca. 3 Ga TDM model ages of Hudson granites, indicate the presence of middle to early Archean crust.

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