Archean and early Proterozoic tectonic framework of north-central United States and adjacent Canada

Abstract

The southern part of the Canadian Shield and the subsurface of the southern interior platform comprise two Archean cratons and three Early Proterozoic collisional orogens. The Middle Proterozoic Midcontinent rift system transects the older rocks in the eastern part of the area. Middle Proterozoic rhyolite-granite complexes overlap these terranes to the south. Anorogenic granite (~ 1.45 Ga) bodies of the Transcontinental Proterozoic province intrude older rocks in a belt extending from Wyoming northeastward to Lake Huron. The two Archean cratons, the Superior and Wyoming provinces, are welded by the Early Proterozoic Trans-Hudson orogen. Sm-Nd data together with differences in lithotypes, structure, and geophysical characteristics demonstrate that the two Archean provinces are not correlative as might be expected by simple lateral extension across the Trans-Hudson orogen. The Superior province consists mainly of alternating greenstone-granite and metasedimentary gneiss terranes (subprovinces) formed = 2.7 Ga that are separated from generally older Archean gneiss to the south by the Great Lakes tectonic zone, a major paleosuture. The Wyoming province, on the other hand, consists of Early to Middle Archean crust that formed between 3.8 and 2.8 Ga. Distinct subprovinces such as are present in the Superior province have not yet been identified in the Wyoming province. The three Early Proterozoic collisional orogens are (1) the Penokean, which extends from the Lake Superior region through the Lake Huron region and in the subsurface from the Lake Superior region to Nebraska, (2) the north-trending Trans-Hudson, and (3) the Central Plains, which truncates the two Archean cratons and the Trans-Hudson and Penokean orogens to the south. The Penokean in the type area (Lake Superior region) consists of a deformed, south-facing, passive continental margin prism (~ 2.2-1.85 Ga), including foredeep deposits, overlying Archean basement that is juxtaposed to the south with accreted juvenile arc rocks of the Wisconsin magmatic terranes. The suture is the north-verging Niagara fault (or shear) zone. The arc rocks formed during the interval 1.9-1.845 Ga. Collision occurred at = 1.85 Ga. In the Lake Huron area, an older asymmetric succession (Huron Supergroup; 2.5-2.2 Ga) of dominantly metasedimentary rocks lies on the continental margin; this sequence was deformed and metamorphosed prior to 2.2 Ga and again, during the Penokean orogeny, at 1.85 Ga. The Trans-Hudson orogen is composed mainly of Early Proterozoic arc-related rocks but includes substantial amounts of Archean basement rocks. In the main outcrop area in northern Saskatchewan, the principal igneous and metamorphic events occurred between 1,910 and 1,830 Ma, approximately contemporaneously with rock-forming events within the Penokean orogen. Seismic reflection profiling at latitude 48°30' N. suggests that both the east and west boundaries of the orogen dip beneath the respective Archean cratons, suggesting subduction beneath the two Archean cratons. Outcrop data in the Hart...