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A Proposed Domainal Reclassification for Saskatchewan's Hearne And A Proposed Domainal Reclassification for Saskatchewan’s Hearne and Rae Provinces C.D. Card Card, C.D. (2012): A proposed domainal reclassification for Saskatchewan’s Hearne and Rae provinces; in Summary of Investigations 2012, Volume 2, Saskatchewan Geological Survey, Sask. Ministry of the Economy, Misc. Rep. 2012-4.2, Paper A-11, 9p. Abstract The last revision of Saskatchewan’s domainal classification for Precambrian rocks was in 2003. New bedrock mapping and analytical data suggest that a revision of domains in the Rae and Hearne provinces is justified. Four changes to the domainal classification are proposed. The first is the combination of the Taltson and Lloyd domains of the Rae Province. The second is the amalgamation of the Mudjatik and Virgin River domains. In addition, the Virgin schist group is to be removed from the Hearne Province (formerly part of the Virgin River Domain) and added to the Taltson Domain. Finally, the Ennadai Domain is to be added to the northeast corner of Saskatchewan. Based on similarities in rock types and ages, rocks of the Taltson magmatic zone, which extends from the Northwest Territories into northeast Alberta and northwest Saskatchewan, continue under the Athabasca Basin into the Lloyd Domain of the Rae Province. It is therefore proposed that the Lloyd Domain be absorbed into the Taltson Domain, currently a small domain of the Rae Province occupying the northwest corner of Saskatchewan. Much of the expanded Taltson Domain lies beneath the Athabasca Basin and therefore its boundary in this region has been determined using aeromagnetic data. When the Virgin River Domain was originally designated, a change in structural style from an arcuate fold pattern of the Mudjatik Domain to a linear straight belt was the principle justification. No change in rock types was cited. New mapping and new geophysical data indicate that the change in structural style is restricted to a small part of the Virgin River Domain and that elsewhere the two domains are indistinguishable. The Virgin schist group, formerly occupying the western part of the Virgin River Domain, will be added to the Taltson Domain to the northwest based on detrital zircon age determinations. The Mudjatik Domain north of the Athabasca Basin gives way to the Ennadai Domain in the northeast part of Saskatchewan. Mapping and follow-up analytical work indicate that the lower amphibolite facies Ennadai group and the high-grade orthogneisses immediately adjacent to it are of similar age and formed in the same tectonic environment. The greatest difference between the Ennadai Domain and the Mudjatik Domain is that the latter lacks the >2.7 Ga supracrustal rocks of oceanic affinity and is instead characterized by <2.6 Ga continental supracrustal rocks. The proposed domain boundary corresponds to the limit of >2.7 Ga orthogneiss units thought to be genetically linked to the high-grade Ennadai group. It corresponds well with transitions in the intensity and structural grain of aeromagnetic and gravity signatures. Keywords: Hearne Province, Rae Province, Mudjatik Domain, Virgin River Domain, Ennadai Domain, Taltson Domain, Virgin schist group, Ennadai group. 1. Introduction The domainal classification for Precambrian rocks in northern Saskatchewan was last revised in 2003 (Saskatchewan Geological Survey, 2003). Since that time, new bedrock mapping and analytical work suggest that some modifications to the present classification are warranted. The western part of the Rae Province in northern Saskatchewan contains the Taltson and Lloyd domains, north and south of the Athabasca Basin, respectively (Figure 1). Bedrock mapping (e.g., Card et al., 2008; Card, 2009), geochronology (e.g., Stern et al., 2003), and geophysical information (Card et al., 2010) suggest that maintaining separate Taltson and Lloyd domains should be re-evaluated. The domainal classification in Saskatchewan’s Hearne Province (Figure 1) has remained largely unchanged since it was proposed in the 1970s (Lewry and Sibbald, 1977). Beginning in 2001, the Saskatchewan Geological Survey conducted significant mapping in all the lithostructural domains of the Hearne Province, including: the Mudjatik north of the Athabasca Basin (e.g., Harper et al., 2001), Peter Lake (e.g., Maxeiner et al., 2011), northern Wollaston (e.g., Harper et al., 2005), Mudjatik south of the Athabasca Basin (e.g., Card and Bosman, 2007), and Virgin River (e.g., Card et al., 2008). This work, together with the interpretation of new Saskatchewan Geological Survey 1 Summary of Investigations 2012, Volume 2 geophysical data (e.g., Buckle et Nolan Ena 60o N Train Dodge 102 W al., 2010) has identified the need Zemlak o for reassessment of the BeaverlodgeRAE Basement Mudjatik subdivisions in the Hearne Tantato Taltson Lake Athabasca Province. Black Lake Taltson zone This publication recommends the following changes to the Athabasca domainal subdivisions in the Rae Carswell Basin Pasfield and Hearne provinces: 1) the Lake tectonic Wollaston Lake combination of the Taltson Domain, in the northwest part of Lloyd the province, and the Lloyd Domain to form a large Taltson Cree Lake Domain that connects with the Snowbird Reindeer Lloyd Peter Lake Wollaston Taltson magmatic zone of Clearwater Lake HEARNE northeast Alberta and the Northwest Territories; 2) the Virgin River Wathaman combination of Virgin River and Mudjatik domains south of the o Athabasca Basin to create a 110 W Mudjatik La Ronge much larger Mudjatik Domain RottenstoneREINDEER ZONE that continues beneath the basin Needle Falls shear zone BBIW and re-emerges to its northeast; Glennie 3) the Virgin schist group should KisseynewNW SASK IW Kisseynew be included in the Taltson Lac Domain and not the Mudjatik La HW Ronge PW Domain; and 4) an Ennadai Alberta PHANEROZOIC Flin Flon Domain carved out of the Saskatchewan Archean Windows Mudjatik Domain and occupying NW = Nistowiak Window IW = Iskwatikan Window Deschambault Sask craton Lake Amisk the northeast corner of the 0 10 30 50 km HW = Hunter Bay Window } Lake PW = Pelican Window province. BBIW = Black Bear Island Window} Hearne 54o N Figure 1 – Current subdivision of lithostructural domains of northern Saskatchewan 2. A Review of Domain and northeastern Alberta. Domains in the Hearne Province are coloured pink, Classification domains in the Rae Province are red, and the Taltson magmatic zone, on the western margin of the Rae Province, is purple. The Clearwater Domain is mostly unexposed Lithostructural domains were and its extent, indicated by dotted lines, is interpreted from aeromagnetic data. The first proposed in Saskatchewan short dashed box represents the extent of Figure 2. by Lewry and Sibbald (1977) in a publication focussed on what is now the Hearne Province south of the Athabasca Basin. Continued geological mapping and follow-up analytical work led to the current classification for the Hearne Province (Figure 1), which was last revised in 2003 (Saskatchewan Geological Survey, 2003). The same holds true for the Rae Province, where numerous changes to the classification have been made north of Lake Athabasca (e.g., Ashton et al., 2005). The Saskatchewan Geological Survey (2003) defines a lithostructural domain is as “a geographic entity, which is distinguished by a distinct lithological and/or structural character.” Variations in metamorphic intensity alone are noted as generally having no influence on the domainal subdivisions. Domain boundaries may be sharp, i.e., defined by a relatively young shear or fault system such as the Needle Falls shear zone, which forms the boundary of the Wollaston and Wathaman domains (Figure 1). In the Rae Province, sharp, structurally controlled boundaries are common. In the Hearne Province, however, the boundaries are more typically transitional in nature and are placed somewhat more arbitrarily out of necessity. The boundary between the Mudjatik and Wollaston domains is a good example. In the original publication proposing the domain, Lewry and Sibbald (1977) stated that “the present work proposes essential lithological, structural and metamorphic continuity between the Wollaston and Mudjatik domains” and went on to emphasize that “the change in structural style which primarily distinguishes the two domains occurs with no indication of tectonic discontinuity.” The Mudjatik/Wollaston boundary is based on contrasting structural styles. The boundary broadly coincides with a change in the typical interlimb angles of regional northeast-trending folds. Gentle to open folds in the Mudjatik Domain give way to close to tight folds in the Wollaston Domain resulting in the linear structural grain originally noted by Lewry and Sibbald (1977). The boundary also loosely corresponds with a decrease in abundance of the basal Daly Lake group of the Wollaston Supergroup both northeast (Card et al., 2006) and southwest (Tran, 2001) of the Athabasca Basin. These two factors make the placement of the boundary subjective, in particular beneath the Athabasca Basin (Figure 2). Saskatchewan Geological Survey 2 Summary of Investigations 2012, Volume 2 Taltson A o Nolan 60 N102 W Train Dodge o Zemlak Ennadai Beaverlodge Tantato Mudjatik Mudjatik Wollaston Taltson Taltson zone Wollaston Peter Lake River shear Taltson Bay Mudjatik Rottenstone Clearwater VirginCable Wathaman 0 25 50 100 Wollaston km B Mudjatik Virgin Bay River zone Mudjatik Wollaston Cableshear Figure 2 – A) Total magnetic intensity (TMI) aeromagnetic map 1 for part of northern Saskatchewan. The interpreted extent of the Mudjatik and Wollaston domains is shown beneath the Athabasca Basin (outlined with a dashed white line). Note that at its northeast end, the Cable Bay shear zone (thin white line) is terminated by nearly perpendicular magnetic trends implying original continuity of magnetic units across any potential Virgin River–Mudjatik domain boundary before the shear zone developed. The same is true at the southwest end of the shear zone. The magnetic signature of the proposed Ennadai Domain has a lower average TMI than that of the Mudjatik Domain and a north-south structural grain. The limit of Phanerozoic cover in the southwest is indicated by a heavy yellow line and the Saskatchewan border by a black dashed line.
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