The Western Craton
|The Black Lake Fault Zone and its southerly extension, the Virgin River Shear Zone defines the eastern margin of the Western Craton. It includes the Firebag, Clearwater and Western Granulite domains in the southwest as well as several domains north of Lake Athabasca. The cratonic rocks have been identified as archaean. They have been overprinted by high temperature/pressure metamorphism (upper amphibolite to granulite facies) by a major tectonic event about 2.5 billion years ago - the Kenoran orogeny. The Archaean rocks themselves were, in part, metamorphosed by the later Hudsonian orogeny to greenschist/amphibolite facies. Granodiorite gneiss dominates the Firebag and Western Granulite domains in the southwest while gabbroic and anorthositic rocks, as well as some supracrustal rocks are also mapped. The Firebag and Western Granulite domains are separated by the Clearwater domain, which Lewry and Sibbald (1977) interpret as "a linear zone of extensive Hudsonian reworking that probably correlates with the Grease River Belt on the north shore of Lake Athabasca". In the northwest (north of Lake Athabasca) the Western Craton is formed mainly by sediments and volcanically-derived supracrustals. Alcock (1936) labelled these rocks the Tazin Group. Later workers (Tremblay, 1978) believe the Tazin Group is Archaean in age. However, it is also probable that some supracrustals are Aphebian (Lewry et al. 1978). Linear zones of intense reworking and shearing (manifested as mylonitization) during Hudsonian time, are also recognized within this part of the craton.|
The Cree Lake Zone
|The Virgin River, Mudjatik and Wollaston domains and their extensions to the northeast are the components of The Cree Lake Zone . It is a distinctive Hudsonian mobile zone, bounded by the Virgin River Shear Zone - Black Lake Fault Zone on the west and the Needle Falls Shear Zone on the east. Lewry, in 1978, defined this mobile zone as a continuous granitoid Archaean basement overlain by Aphebian supracrustals that are mainly derived from sediments that were eroded into the waters along the Western Craton margins. During the Hudsonian orogeny the mobile core of the Cree Lake Zone (the Mudjatik domain) metamorphosed into flat lying, high temperature/pressure, migmatized lobes of basement rocks, with incorporated lesser supracrustals. The Virgin River and Wollaston domains are the bread to the Mudjatik sandwich. They are mainly lower temperature gneisses composed of Archaean granitoid basement cores enveloped by Aphebian supracrustals. Logically, the metamorphic grade can be traced away from heat source as granulite facies is noted in the core and lower amphibolite /greenschist facies at the margins (Lewry, 1978).|
The Rottenstone Domain
|The Rottenstone Domain comprises a gradational eastern boundary with the western La Ronge domain. It is a broad belt of early to late syntectonic Hudsonian tonalitic to granitic intrusive rock and associated injection migmatites lying east of the Needle Falls Shear Zone. Intruded more recently, the Wathaman Batholith forms an intrusive body of major proportions (at least 1200 kilometers in width) across Saskatchewan within the domain.|
|This inclusive crustal unit is a combination of the La Ronge, Glennie Lake, Kisseynew
and Flin Flon domains. It is composed of Aphebian to early Hudsonian island arc
volcanics and associated volcanogenic sediments, related intrusives and incorporated sub-
arc crust, as well as later flysch type deposits. Archaean or early Aphebian crustal
remnants in the Hanson Lake area mapped by Coleman in 1970 may represent
microcontinental fragments within the Aphebian oceanic crust.
With canoeing in Saskatchewan concentrated in this complex, it is appropriate to describe the geology in more detail.