Pb isotopic data are reported for whole-rock samples and feldspars from two parts of the 1.9–1.8-Ga-old Trans-Hudson Orogen in Canada — the Reindeer Zone in Saskatchewan, and the Ottawa and Belcher Islands in Hudson Bay. The first area contains a variety of volcanic, granitoid and sedimentary rocks in several oceanic and magmatic arcs aligned parallel to the margin of the Archean Hearne Craton; the second is part of the Circum-Superior belt, a belt of oceanic basalts and sedimentary rocks that surrounds the Superior Craton.In several regions, Pb-Pb isochrons gave ages generally consistent with available geochronological or geological data (Flin Flon, 1822 ± 44 Ma (2σ); Peter Lake Complex, 2710 ± 220 Ma; Ottawa Islands, 1790 ± 80 Ma; Belcher Islands; 1960 ± 160 Ma). In other regions the Pb-Pb age was too low, reflecting disturbance of the Pb system (e.g., La Ronge belt, 1730 ± 115 Ma) or too high, perhaps because of contamination of certain samples with older crust (e.g., Wathaman Batholith, 2200 ± 200 Ma).Model μ-values and Th/U ratios calculated from the Pb data are interpreted in terms of variations in the compositions of mantle sources, complicated by contamination with material from the upper or lower continental crust. In the southern part of the Reindeer Zone, and in volcanic rocks from the Ottawa Islands, model μ-values vary from 8.0 to 8.1 and correlate inversely with initial ϵNd-values. This variation is thought to result from contamination of juvenile material (μ ≈ 8.0) with material from Archean upper crust, which had low ϵNd but relatively high μ. In the northern part of the zone, and in Eskimo Formation basalts from the Belcher Islands, μ-values remain constant or decrease as ϵNd declines, and this is attributed to contamination with U-depleted lower crust. Calculated Th/U ratios vary from 1.34 to 6.67. The lowest values (1.4–1.8) come from mafic to felsic volcanic rocks of the Flin Flon and western La Ronge belts. These low Th/U-values are like those in modern island arc volcanics, and are attributed to enrichment of U in the source. Slightly higher values are calculated for oceanic basalts from the Circum-Superior belt. MORB-like basalts from the Ottawa Islands have a low Th/U of 2.5, reflecting depletion of Th along with other incompatible elements; higher values of 3.9 characterize the more enriched Flaherty basalts. The highest Th/U-values, which are found in samples with the lowest ϵNd and low μ-values (Wathaman Batholith and Eskimo basalts), are thought to reflect the high Th/U of the U-depleted lower-crustal contaminant.These results have several interesting implications. The similarity between the isotopic and chemical characteristics inferred for these 1.9-Ga-old rocks and those of volcanics in modern convergent margin settings provides further indication that the tectonic and petrogenetic processes peculiar to modern subduction environments operated in the middle Proterozoic. The apparent presence of material from the lower and upper crust in the sources of the granitoids indicates that these rocks were not derived from subducting oceanic plate or the mantle wedge, but probably formed and evolved within the crust itself.