TWO TRANSECTS ACROSS THE SNOWBIRD TECTONIC ZONE, WESTERN CHURCHILL PROVINCE: EXPLORING THE CONTINUITY OF THE RAE-HEARNE BOUNDARY AND ITS ROLE DURING THE GROWTH OF LAURENTIA

The Snowbird tectonic zone is a 2800 km long geophysical lineament extending across the western Churchill Province of the Canadian Shield. It was originally considered the boundary between the Rae and Hearne domains of the western Churchill Province, one of the Proterozoic “United Plates” sutures along which the North American craton assembled. However, the origin and tectonic significance of the Snowbird zone persists as a major problem in the evolution of the western Canadian Shield. Detailed geochronologic, isotopic, structural, and geochemical data from transects across the lineament in northern Saskatchewan (transect 1) and Angikuni Lake, Nunavut (transect 2) call into question current interpretations that envisage Paleoproterozoic (1.9 Ga) suturing of the Rae and Hearne domains. Both transects display Neoarchean continuity across the lineament with no discernible break in the Nd or Hf isotopic compositions of plutonic rocks. Both 2.60 Ga granitic rocks and 2.60-2.53 Ga tectonism persist unimpeded across the lineament. In-situ monazite geochronology suggests regional Paleoproterozoic (1.9 Ga) tectonism in a large swath of the southern Rae domain, but not at the latitude of Angikuni Lake. Both regions were segmented by localized post-1.9 Ga deformation resulting in the juxtaposition of various lithotectonic blocks that vary in structural style, rock type, and grade of metamorphism. In-situ micro zircon geochronology of the Chipman (transect 1) and Kazan (transect 2) dike swarms suggests 2.1 Ga mafic magmatism along more than 800 km of the Snowbird zone. These dikes are similar in age and composition to the Griffin gabbro sills, which cut the Hurwitz Group in the Hearne domain, and are likely distal equivalents. Thus, unlike other Paleoproterozoic boundaries in the United Plates model, the Snowbird zone is not a suture. Instead, it is a composite feature that experienced Neoarchean tectonism, aborted rifting at 2.1 Ga, and repeated Paleoproterozoic reactivation, when it acted as an intracontinental weak zone during the assembly of the Nuna Supercontinent.