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The composition, chronology, and structural relations of the Saskatchewan Craton and enveloping mylonitic rocks exposed in basement windows of the Glennie Domain, Trans‐Hudson Orogen, have been determined by geochemical, geochronologic, and structural studies accompanying detailed field mapping. Basement windows lie along the hinge zone of a regional crustal culmination and consist mostly of 2.4–2.5 Ga felsic plutonic rocks enveloped by the Nistowiak Thrust. The Nistowiak Thrust is a folded, 1–2 km thick, upper amphibolite facies mylonite zone formed during emplacement of the Flin Flon–Glennie Complex across the Saskatchewan Craton. It is likely correlative to the Pelican Thrust, which envelops basement windows in the Hanson Lake Block ∼100 km to the east. An internal high strain zone within the overlying nappe pile, the Guncoat Thrust, is composed primarily of mylonitized porphyroclastic pelitic and psammitic migmatites. U‐Pb geochronological results suggest calc‐alkaline plutonism from 1889–1837 Ma, thr...

Lead isotopes are sensitive indicators of crustal interaction in arc magmatism because of the large contrast in lead concentration between mantle-derived magmas and continental crust and the three independent decay paths in the U-Th-Pb system. Preserved within Wopmay Orogen (1.94 to 1.84 Ga) are the remnants of three magmatic arcs. The isotopic composition of lead in alkali feldspars separated from a diverse suite of samples from all three arcs fall in a relatively tight cluster with $^{206}Pb/^{204}Pb = 15.59-15.88$, $^{207}Pb/^{204}Pb = 15.27-15.36$, and $^{208}Pb/^{204}Pb = 35.15-35.54$, except for samples from the only plutonic suite within Wopmay Orogen observed to intrude Archean crust. Plutons intruding Archean crust have $^{206}Pb/^{204}Pb = 15.29-15.49$, $^{206}Pb/^{204}Pb= 15.23-15.31$, and $^{208}Pb/^{204}Pb = 35.21-35.30$. Lead isotopic compositions do not correlate with rock composition: both diorites and peraluminous granites have the same lead isotopic composition. This isotopic composition...