Sm–Nd isochron from a granodiorite–granite complex in the Portman Lake region, Northwest Territories
Whole-rock samples for a granodiorite–granite intrusion in the Portman Lake area of the Northwest Territories yield an Sm–Nd isochron with an age of 2577 ± 36 Ma. The addition of a garnet analysis results in an age of 2562 ± 21 Ma. An Sm–Nd isochron is rare for granitic samples because of small rang...
| Published in: | Canadian Journal of Earth Sciences |
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| Main Authors: | , , |
| Format: | Article in Journal/Newspaper |
| Language: | French |
| Published: |
Canadian Science Publishing
1989
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1139/e89-232 http://www.nrcresearchpress.com/doi/pdf/10.1139/e89-232 |
| Summary: | Whole-rock samples for a granodiorite–granite intrusion in the Portman Lake area of the Northwest Territories yield an Sm–Nd isochron with an age of 2577 ± 36 Ma. The addition of a garnet analysis results in an age of 2562 ± 21 Ma. An Sm–Nd isochron is rare for granitic samples because of small ranges in 147 Sm/ 144 Nd values and variability in the initial Nd isotopic ratios. A wide range in 147 Sm/ 144 Nd values among samples in this study is considered a result of garnet fractionation and (or) variable concentrations of titanite in the samples. The ε Nd values for the initial Nd isotopic ratios of the isochrons are essentially zero or bulk Earth values. The evolution of the intrusion at 2.56 Ga reflects either the remelting of (2.7–2.8 Ga) preexisting continental crust or the mixing of depleted mantle material and crust older than 2.8 Ga. In either case, the data argue for a crustal history of at least 200 Ma prior to the intrusion of the complex in this section of the Churchill Province. |
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