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TitleEvidence for Neoarchean Ni-Cu-bearing mafic intrusions along a major lithospheric structure: a case study from the south Rae craton (Canada)
AuthorRegis, D; Acosta-Gongora, P; Davis, W J; Knox, B; Pehrsson, S; Martel, E; Hulbert, L
SourcePrecambrian Research 2017., https://doi.org/10.1016/j.precamres.2017.09.026
Year2017
Alt SeriesNatural Resources Canada, Contribution Series 20170087
PublisherElsevier
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceManitoba; Northwest Territories; Saskatchewan; Nunavut
NTS75A; 75B; 75C; 75F; 75G; 75H; 74N; 74O; 74P; 65C; 65F; 64K; 64N
AreaThye Lake; Yotin-Shagory Lake; Currie Lake; Axis Lake
Lat/Long WENS-110.0000 -100.0000 62.0000 59.0000
Subjectsgeochronology; mafic rocks; ultramafic rocks; intrusive rocks; paragneisses; nickel; copper; mineralization; metamorphic petrology; crystallization; zircon dates; uranium lead dates; Snowbird Tectonic Zone; Hearne craton; Rae craton; geochronology
Illustrationslocation maps; tables; geological sketch maps; photomicrographs; photographs; phase diagrams; Concordia diagrams
ProgramSouth Rae Province Bedrock/Surficial geology, GEM2: Geo-mapping for Energy and Minerals
AbstractDeformed and metamorphosed mafic to ultramafic intrusive rocks are common along and adjacent to the Snowbird Tectonic Zone, a major Paleoproterozoic structure separating the Rae and Hearne cratons. On the Rae side of this major lithospheric structure, we investigated a series of mafic bodies that intrude high-grade paragneiss and are associated with Ni - Cu±PGE mineralization. By linking field observations, geochronology and metamorphic petrology, our results indicate Archean (~2.63 Ga) crystallization ages for these mafic intrusions over a minimum along-strike extent of ?500 km and a later high-temperature (~820°C and ~7.5 kbar), Paleoproterozoic metamorphic overprint at t < 1.94 Ga. The youngest reproducible ages of detrital zircon from the host paragneiss indicate a maximum depositional age of ~2.73 Ga for the paragneiss. These results indicate that the sedimentary rocks hosting the mineralized mafic intrusions are older than the mixed siliciclastic and carbonate sedimentary units previously described along the Snowbird Tectonic Zone (< 2.07 Ga). Furthermore, in two localities (Thye and Yotin-Shagory lakes, in Northwest Territories and northern Saskatchewan), zircon from both the mafic and pelitic samples exhibit an unusual within-run fluctuation in the lead isotope signal during SHRIMP analysis, suggesting inhomogeneous redistribution of radiogenic Pb within the crystal lattice. Redistribution is interpreted to have occurred during the ~1.94 - 1.90 Ga tectonometamorphic event. This behaviour, documented only in ~10 (Ultra)High-Temperature localities worldwide, has not been observed in the other two studied localities (Currie and Axis lakes in northern Saskatchewan), suggesting either i) a different metamorphic history or ii) different re-crystallization processes occurring during the Paleoproterozoic high-temperature evolution (or a combination of the two). Our data indicate that (U)HT metamorphism and the absence of a fluid/melt phase are not a requirement for lead redistribution in zircon.
Summary(Plain Language Summary, not published)
Deformed and metamorphosed mafic to ultramafic intrusive rocks are common along and adjacent to the Snowbird Tectonic Zone, a major Paleoproterozoic structure separating the Rae and Hearne cratons. On the Rae side, we investigated a series of mafic bodies that intrude high-grade paragneiss and are associated with Ni-Cu±PGE mineralization. By linking field observations, geochronology and metamorphic petrology, our results indicate Archean (~2.63 Ga) crystallization ages for these mafic intrusions and a later high-temperature metamorphic overprint during the Proterozoic at t < 1.94 Ga. Zircon from both the mafic and pelitic samples exhibit an unusual within-run fluctuation in the lead isotope signal during SHRIMP analysis, suggesting inhomogeneous redistribution of radiogenic Pb at ~1.94-1.90 Ga within the crystal lattice. Our data indicate that (U)HT metamorphism and the absence of fluids are not a requirement for lead redistribution in zircon.
GEOSCAN ID301696