COLLISIONAL OROGENESIS AT CA. 2.35 GA IN THE RAE DOMAIN, WESTERN CHURCHILL PROVINCE, NUNAVUT, CANADA

Structural, metamorphic, and in-situ SHRIMP geochronological data from an Archean supracrustal belt (Committee Bay) in the northern Rae domain challenge the view that the western Churchill Province experienced protracted ca. 2.5-2.1 Ga extension leading to the breakup of a late Archean (Kenorland) supercontinent and deposition of the lower Hurwitz Group (Aspler et al. 2001). Within D2 strain shadows of an Archean pluton, S1 is recognized as a N-striking, E-dipping foliation associated with W-vergent D1 folds and possible thrusts. Porphyroblast-fabric relationships in metapelitic rocks demonstrate that regional M1 metamorphism occurred syn- to post-D1 (and M2 occurred syn- to post-D2). Monazite inclusions in late- to post-D1 garnet and staurolite yield a 2345 ± 6 Ma age population that, on the basis of microtextural features, effectively dates M1 at a late stage of D1 strain. M2 is dated by 1838 ± 5 Ma matrix monazite. Thermobarometric data, quantitative pseudosections, and petrographic textures indicate a clockwise P-T-t path for M1.

The absence of ca. 2.35 Ga plutonic rocks, together with a clockwise P-T-t path and porphyroblast growth late during D1 contractional strain, collectively point to metamorphism as a consequence of crustal thickening. The compressional forces that drove ca. 2.35 Ga thickening may reflect the far-field effects of collisional orogenesis following a period of continental arc magmatism on the western Rae margin (cf. Hoffman, 1988). This is supported by 1) ca. 2.4 and 2.35 Ga EMPA monazite ages that we have determined from upper-amphibolite paragneiss in the Queen Maud block; 2) ca. 2.4-2.3 Ga granitoid rocks of the Taltson basement complex (e.g. McNicoll et al. 2000; Bostock et al. 1991); and 3) the syn-collisional chemistry of ca. 2.3 Ga granitoids of the Beaverlodge domain (Hartlaub et al. 2003). Tectonometamorphism at ca. 2.35 Ga across the Rae domain may have initiated intracratonic deposition of the lower Hurwitz Group, with extension not becoming established in the Rae before the onset of ca. 2.19 Ga mafic magmatism.

Bostock et al. (1991) Geol. Surv. Canada Curr. Res. 90-2, 67-78. McNicoll et al. (2000) Can. J. Earth Sci. 37, 1575-1596. Hartlaub et al. (2003) GAC-MAC abstracts 28, 659. Aspler et al. (2001) Sediment. Geol. 141-142, 287-318. Hoffman (1988) Ann. Rev. Earth Sci. 16, 543– 603