A Proposed Domainal Reclassification for Saskatchewan's Hearne and Rae Provinces

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 2.7 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.