Tectonic History of the Southwestern Margin of the Rae Province in Northwestern Saskatchewan

Summary The southwestern Rae margin in northwestern Saskatchewan includes 3.01-2.94 Ga and 2.62-2.58 Ga granitoids typical of the Rae Province. The Arrowsmith Orogen produced 2.37 Ga metamorphism and 2.33-2.30 Ga post-collisional granitoid rocks. Initial deposition of the Murmac Bay group at about 2.33 Ga was derived from an unknown Paleo- to Mesoarchean source; higher stratigraphic levels record diverse locally exposed rocks and a 2.2-2.0 Ga suite possibly exposed to the west. Multiple terrane accretions during the Taltson Orogen produced a 1.94-1.92 Ga southeast-striking regional foliation, which was overprinted by a 1.91-1.90 Ga northeast-striking fabric associated with tectonism along the Snowbird Tectonic Zone. Circa 1.84-1.83 Ga terrane accretion farther west and terminal collision in the Trans-Hudson Orogen resulted in widespread faulting, deposition of the Martin Group, and the historic Beaverlodge uranium and gold deposits. Abstract Integration of data from the southwestern margin of the Rae Province in Saskatchewan and the Taltson Magmatic Zone to the west is shedding more light on the region’s tectonic history. The oldest rocks include 3.01-2.94 Ga granitoids (Hartlaub et al., 2004; Ashton et al., 2009) south of Uranium City and 3.2-3.1 Ga granitoid gneisses in the basement complex to the Taltson Magmatic Suite (McNicoll et al., 2000), which may link under the Athabasca Basin (Fig. 1). Much of the remaining area in northwestern Saskatchewan is underlain by 2.62-2.58 Ga and rare 2.71 Ga granitoid basement, which may not be represented in the Taltson Magmatic Zone but is characteristic of the Rae Province elsewhere (e.g. LeCheminant and Roddick, 1991). In the northern Rae Province, ca. 2.50-2.46 Ga granitoid rocks emplaced the Queen Maud Block were attributed to rifting by Schultz et al. (2007). Based on subsequent widespread 2.39-2.34 Ga metamorphism (Fig.1; Berman et al., 2005; Schultz et al., 2007), the granitoids were alternatively interpreted as a continental arc by Berman et al. (2007) and the metamorphism attributed to the Arrowsmith Orogen involving terrane accretion on the western flank of the Rae Province (Berman et al., 2005). Early 2.5-2.4 Ga granitoids have not been recognized in northwestern Saskatchewan, but 2.45-2.38 Ga felsic to intermediate plutonic rocks are exposed in the eastern Taltson Magmatic Zone (van Breemen et al., 1987; Bostock and Loveridge, 1988; McNicoll et al., 2000). Late 2.33-2.29 Ga post-collisional granites are emplaced in the Archean granitoids at Uranium City (Hartlaub et al., 2007), and occur as a component of strongly magnetic felsic to intermediate orthogneiss west of Uranium City (Ashton et al., 2007a) and along strike in the easternmost Taltson Magmatic Zone (Bostock et al., 1991; van Breemen and Bostock, 1994; McNicoll et al., 2000). In Saskatchewan, Arrowsmith metamorphism is recorded

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