CRUSTAL HISTORY OF THE RAE AND HEARNE PROVINCES, SOUTHWESTERN CANADIAN SHIELD, SASKATCHEWAN - CONSTRAINTS FROM GEOCHRONOLOGICAL AND ISOTOPIC DATA

The Cree Lake Zone (Hearne Province) and Western Granulite domain (Rae Province), in northern Saskatchewan, are contrasting parts of the var iably reworked, (?) upper plate western hinterland of the Paleoprotero zoic Trans-Hudson Orogen. Their junction is defined by the Virgin Rive r Shear Zone, a part of the more extensive Snowbird ''tectonic zone''. Subsurface extension of the approximately 2.0 Ga Thelon Orogen lies w est of the Western Granulite domain. We present U-Pb zircon ages, Sm-N d and Rb-Sr isotopic data from the Cree Lake Zone and Western Granulit e domain, and from the Junction Granite which intrudes the Virgin Rive r Shear Zone. Data from the Western Granulite domain indicate that pre valent granulite facies metamorphism occurred between approximately 2. 3 and 2.0 Ga, but is imposed on Archean protoliths approximately 2.8-3 .0 Ga old. Low amphibolite facies retrogression, which increases towar d the Virgin River Shear Zone, probably postdates 2.1 Ga. Data from th e Cree Lake Zone also yield Archean protolith ages as old as 3.0 Ga, a nd some rocks yield interpreted high-grade metamorphic overprint ages of approximately 2.3-2.0 Ga. However, two samples yield data indicatin g ''Hudsonian'' high-grade metamorphic overprint approximately 1.87 to 1.81 Ga. The Junction Granite has a U-Pb zircon age of 1.82 +/- 0.30 Ga, but relict zircons and Sm-Nd data show that it was derived by melt ing of Archean crust. High-grade mid-crustal thermal resetting in the Western Granulite domain may be coeval with the 1.9-2.0 Ga Thelon Orog en, although the data do not preclude an earlier event or events. Simi lar, approximately 2.3-2.1 Ga reworking extends into the Cree Lake Zon e, but high-grade ''Hudsonian'' (1.87-1.84 Ga) reworking is also evide nt in parts of this zone well to the west of the Wollaston domain, and may extend entirely across the zone to the Virgin River Shear Zone. R elative importance of the ''Thelon'' and ''Hudsonian'' overprints in C ree Lake Zone is unknown. Data from the Junction Granite and Western G ranulite domain suggest that all recorded high-strain events in the Vi rgin River Shear Zone postdate approximately 2.3 Ga and are thus unrel ated to deep-crustal Archean granulite facies mylonites in the Tantato -Black Lake segment of the Snowbird tectonic zone, north of the Athaba sca basin.