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Paleoproterozoic arc magmatism imposed on an older backarc basin: Implications for the tectonic evolution of the Trans-Hudson orogen, Canada

Pete Hollings^*,1 and Kevin Ansdell^,1

¹ Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada

Compositional data from 72 granitoids and associated mafic rocks in the Paleoproterozoic Kisseynew domain, Trans-Hudson orogen, Canada, were used to evaluate the tectonic setting of magma generation between 1840 and 1820 Ma. These data thus provide insights into the development of the Trans-Hudson orogen just prior to amphibolite-grade metamorphism and the final stages of continental collision.

The granitoid rocks are hornblende- or orthopyroxene-bearing, medium- to high-K calc-alkalic, and weakly peraluminous. The trends on Harker variation diagrams are consistent with crystal-fractionation processes, although the range in values is related to the temporal and spatial distribution of samples. The extent of LREE (light rare earth element) enrichment increases with increasing SiO₂, as does variability in HREE (heavy rare earth element) fractionation and magnitude of Eu anomalies. Most samples have (Gd/Yb)_n < 10 (suite Ia), although five have (Gd/Yb)_n = 17–24, suggesting the presence of garnet residua (suite Ib). The range in rock types, calc-alkalic character, and negative Nb and Ti anomalies are all characteristic of arc environments. Magma generation within the Trans-Hudson orogen, including the Kisseynew domain, between 1.84 and 1.82 Ga was related to interaction between the Sask craton and the Flin Flon–Glennie complex. A decrease in subduction angle likely resulted from northward-directed subduction of more buoyant crust, with associated changes in thermal conditions leading to melting over a wide area. Most magmas formed in a slab-dehydration–dominated regime, although localized slab melts may have been generated. Ultimately subduction ceased, and the slab foundered into the mantle, potentially resulting in the generation of alkalic and potassic magmas within the Rae and Hearne cratons.

Key Words: geochemistry • granitoid • Kisseynew domain • tectonic models • Trans-Hudson orogeny