Formation of Canadian 1.9 Ga old continental crust. I: Nd isotopic data

• Published in: Canadian Journal of Earth Sciences
• Main Authors: Chauvel, C., Arndt, N. T., Kielinzcuk, S., Thom, A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1987
• Subjects: General Earth and Planetary Sciences; Belcher Islands; Churchill; Hudson Bay; Ottawa Islands; Reindeer Lake
• Online Access: http://dx.doi.org/10.1139/e87-042; http://www.nrcresearchpress.com/doi/pdf/10.1139/e87-042

A Nd isotopic study was carried out on 1.9−1.8 Ga rocks from two parts of the Trans-Hudson Orogen in northern Canada. The first part is the Reindeer Lake Zone in the Churchill Province in Saskatchewan, where a variety of volcanic, granitoid, and sedimentary rocks are preserved in several lithotectonic belts that border a reworked Archean craton to the northwest. The second area comprises the Ottawa and Belcher islands, in Hudson Bay, and the Fox River volcanics, in Manitoba. These form part of the Circum-Superior Belt, a band of basaltic volcanics and sedimentary rocks that overlies the Archean Superior craton.From U–Pb zircon ages, Pb–Pb ages, and Sm–Nd ages, Nd initial isotopic compositions were calculated for all analyzed samples. In the Saskatchewan terrains, we obtained a large range of ε Nd values, from +5 to −8. The highest values (+4 to +5) come from two volcanic-dominated belts (Flin Flon and Western la Ronge), lower values (~+2) characterize intervening sediment-dominated domains (Eastern La Ronge, Glennie Lake, and Kisseynew), and still lower values (−1 to −4) were found in migmatitic and granitoid belts adjacent to the reworked Archean craton in the northwest. Each lithotectonic belt has its own characteristic, restricted range of ε Nd values, and, with few exceptions, there is no correlation between ε Nd and rock type; i.e., in individual belts, volcanics, granites, and sediments have very similar ε Nd values.In the Circum-Superior Belt, three lava flows from the Ottawa Islands have ε Nd values ranging from +4.5 to 0, and samples from the Belcher Islands have values ranging from +3.5 to −9.These results are explained by mixing between mantle-derived rocks and variable amounts of Archean continental crustal rocks. Assuming that 1.9 Ga ago the mantle had an ε Nd value of +5 and Archean crust had an ε Nd value of −12, we calculate proportions of Archean crustal material in Trans-Hudson rocks ranging from ~2 to 35 %, increasing systematically toward the Archean platform. The mean Archean component is ...