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New U–Pb geochronological and Sm–Nd isotopic data establish the timing of Neoarchean and Paleoproterozoic magmatic and metamorphic events in northeastern Saskatchewan, and give insight into the late Archean assembly of the central and southern Hearne domains of the western Churchill craton. Tonalite orthogneiss within a migmatite complex is 2714 ± 6 Ma in age. Foliated, tonalite gneiss, typical of tonalitic rock that intruded the migmatite complex and mafic volcanic rocks of the Ennadai Group, is 2698 ± 6 Ma in age. These and a third tonalitic gneiss are correlative with ca. 2.72–2.70 Ga volcanic and plutonic rocks previously documented in the Central Hearne supracrustal belt (CHSB). They have juvenile geochemical signatures (ɛNd > 1.43). A rhyolite dated at 2681 ± 4 Ma is consistent with the age and juvenile nature of a younger volcanic cycle in the CHSB. In contrast, a 2681 ± 3 Ma foliated granite dyke that intrudes the tonalite gneiss contains inherited zircons up to 2.99 Ga and has an ɛNd of −0.48, consistent with a melted older Mesoarchean crustal component similar to that of the southern Hearne domain. Three Paleoproterozoic granites also have Nd isotopic signatures consistent with Mesoarchean precursors. We propose that the abrupt change in geochemical signature of the ca. 2.68 Ga magmatism is due to the accretion of the CHSB onto the southern Hearne domain and a change from oceanic to continental arc magmatism. A 2571 ± 5 Ma in situ monazite age determined for porphyroclastic gneiss in the Striding–Athabasca mylonite zone is linked with latest Archean reactivation along the southeastern margin of the Rae province. The Jones Lake granite, dated at 1.86 ± 0.02 Ga, yielded metamorphic monazite ages from 1821 Ma to 1812 Ma. An amphibolitic gneiss yielded a multi-grain, TIMS, zircon age of 1823 ± 4 Ma. The latter ages agree well with the time of metamorphism determined by in situ monazite SHRIMP ages from three samples of metasedimentary gneiss (1826 ± 8 Ma, 1817 ± 42 Ma and 1809 ± 38 Ma), and coincide with the peak of Hudson granite emplacement in the Western Churchill craton. A diatexitic granodiorite crystallized at 1812 ± 4 Ma. U–Pb titanite analyses from three separate rocks yielded ages of 1778 ± 2 Ma, 1761 ± 2 Ma and 1757 ± 5 Ma, while U–Pb from rutile yielded 1751 ± 12 Ma. The 1830–1800 Ma events appear to be related to terminal collision within the Trans-Hudson Orogen, while the younger titanite and rutile ages are cooling ages coeval with emplacement of the Nueltin igneous suite. |
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