An Overview of Grenville Province Geology, Canadian Shield

Abstract

The last major event that shaped the Canadian Shield, orogeny during the mid- to late Mesoproterozoic, left its imprint as a broad swath of highly deformed and metamorphosed rocks extending 2000 km from the Atlantic coast of southern Labrador to Lake Huron. The northwest margin of the resulting Grenville Province, referred to as the Grenville Front, is a zone of southeasterly dipping thrust faulting and mylonitization that truncates the various structural trends characterizing the adjacent, older shield provinces. Some 400–500 km farther southeast, the exhumed Grenville Province is overlain by lower Paleozoic platformal sedimentary rocks, but crystalline rocks bearing the imprint of Grenvillian orogenic events appear again in tectonic windows within the Appalachian Orogen of Maritime Canada and the eastern United States. Beyond its exposure in the Canadian Shield, the Grenville Orogen extends southwestward to Texas and Mexico; it is also recognized in inliers in the Caledonides of Northern Ireland, Scotland, and Norway, southeast of which it is represented by the Sveconorwegian Province of southern Norway and Sweden (Fig. 3.1). Recent reconstructions of supercontinent assembly in the early Neoproterozoic (e.g. Dalziel, 1991; Moores, 1991; Hoffman, 1991; Borg and DePaolo, 1994) show a further continuation of this belt from central America through Antarctica and eastern India to Australia. The widely used term “Grenvillian Orogeny” embraces a range of tectonic events beginning with an early accretionary stage between ca. 1.3 and 1.2 Ga, and ending with uplift and exhumation shortly after 1.0 Ga. Arguing that the construction of orogens involves more than