Geology of the Reindeer Lake area, Saskatchewan, with emphasis on granitic rocks
Fumerton, Stewart Lloyd
Reconnaissance geological mapping has been carried out on 8500 sq km centered on the northern part of Reindeer Lake in northern Saskatchewan. Parts of four major litho-structural domains occur in the area: from northwest to southeast they are the Whiskey Jack Domain, the Rottenstone Domain, the La Ronge Domain, and the Kisseynew Domain. This map area lies primarily in the Rottenstone Domain. The Whiskey Jack Domain (a new name proposed here) includes an Archaean granite basement overlain by the Aphebian Wollaston metasedimentary gneisses, both of which have been partially remobilized during the Hudsonian Orogeny. In the northwest, the Rottenstone Domain contains granitoid and younger gabbroic rocks, both of possible Archaean age. Large areas in the central portion of the domain are underlain by rocks of the Hudsonian Wathaman Batholith. In the southeastern part of the domain, Aphebian migmatitic and metasedimentary gneisses are intercalated with granitic rocks. The La Ronge Domain consists principally of granodioritic bodies, forming part of the South Reindeer Batholith (a term proposed in this study). It also contains the La Ronge metasedimentarymetavolcanic gneisses. Both granites and gneisses were folded during the Hudsonian Orogeny. The Kisseynew Domain is restricted to a small area. It contains both the La Ronge and Burntwood River gneisses, which are intercalated with deformed granitic bodies. Twenty five major rock units were mapped, these include metasedimentary and metavolcanic rocks, mylonites, basic and granitic rocks. Major element chemistry indicates that some of the granitic rocks have been magmatically fractionated. Field evidence indicates that other granitic bodies possibly have been formed by metasomatism and anatexis especially near the southern contact of the Wathaman Batholith, a conclusion not completely supported by the major element chemistry. The present study establishes that the Needle Falls Shear Zone and the Wathaman Batholith together are related to a major crustal discontinuity. Rocks northwest of the discontinuity include both Archaean basement material and Aphebian supercrustal rocks, whereas rocks to the southeast are entirely Aphebian. The Wathaman Batholith and the Needle Falls Shear Zone formed during the peak of Hudsonian tectonothermal activity in this part of the Churchill Province of the Canadian Shield. The Wathaman Batholith, one of the largest in the world, is 1100 km long and 40 to 60 km wide. The isotopic and REE compositions of rocks from the batholith indicate that the magma was probably derived by the fusion of pre-existing continental crust at great depth. Garnet, amphibole, and hypersthene were probably major residual phases in the source region during the formation of the magma. Concomitant with emplacement of the Wathaman Batholith, pre-existing granitic and metasedimentary rocks southeast of the batholith were tectonically 'rolled up' in a polyphase deformation sequence, and slightly younger migmatites and autochthonous-allochthonous granites were formed immediately adjacent to the batholith. The structural fabric of the schists and gneisses was formed by complex superposition and transposition of foliations, some of which are axial planar to folds though others are related to shear zones. The emplacement of the Wathaman Batholith was preceded by the emplacement of the large South Reindeer Batholith of Aphebian age. This batholith parallels the Wathaman Batholith, intrudes the Burntwood River gneisses, and appears to be unconformably overlain by the La Ronge gneisses. The Wathaman and South Reindeer Batholiths are paired batholiths and are analogous to the large paired batholiths in the Western Cordilleras. Note:This thesis contains maps that have been sized to fit the viewing area. Use the zoom in tool to view the maps in detail or to enlarge the text.