The Lake Superior region and Trans-Hudson orogen
Published:January 01, 1993
P. K. Sims, J. L. Anderson, R. L. Bauer, V. W. Chandler, G. N. Hanson, J. Kalliokoski, G. B. Morey, M. G. Mudrey, Jr., R. W. Ojakangas, Z. E. Peterman, K. J. Schulz, S. B. Shirey, E. I. Smith, D. L. Southwick, W. R. Van Schmus, P. W. Weiblen, 1993. "The Lake Superior region and Trans-Hudson orogen", Precambrian, John C. Reed, Jr., Marion E. Bickford, R. S. Houston, Paul Karl Link, D. W. Rankin, Paul K. Sims, W. Randall Van Schmus
Download citation file:
Precambrian rocks in the Lake Superior region underlie all or parts of Minnesota, Wisconsin, and Michigan, an area along the southern margin of the Superior province of the Canadian Shield (Fig. 1). Except on the north, adjacent to Canada, the Precambrian rocks are overlapped by sedimentary strata of Paleozoic and Mesozoic age, which constitute a thin platform cover of relatively undisturbed rocks that thicken to the west, south, and east. Inliers of Precambrian rocks are exposed locally in southern Minnesota and Wisconsin, mainly in the flat valleys of major rivers, where erosion has cut below the Phanerozoic strata. The present landscape is subdued, and is inherited largely from Pleistocene continental glaciations, which produced a variety of erosional and depositional landforms. The glacier ice scoured the bedrock in the northern parts of the region, in much the same way as throughout most of Canada, and deposited materials of diverse lithology and provenance, as much as 200 m thick, over much of the remainder of the region. The Precambrian rocks in the region record an extended interval of crustal development and evolution that spans nearly 3 b.y. of earth history. This interval of geologic time is not continuously recorded in layered and intrusive units, but instead is punctuated by specific rock-forming and tectonic events that can be deduced from geologic relations and placed in a chronometric framework by isotopic dating. (Fig. 2, also see correlation chart for Precambrian rocks of the Lake Superior region, Morey and Van Schmus, 1986; and Bergstrom and Morey, 1985.)
Figures & Tables
This wide-ranging discussion of Precambrian rocks includes contributions from a diverse array of authors actively engaged in investigations of various aspects of U.S. Precambrian geology. Summary discussions by the editors of the five major chapters place these contributions in a logical regional framework. A concluding chapter explores Archean crustal processes from the point of view of lunar and planetary analogies, discusses the significance of Sm crustal provinces, and provides an overview of the development of the southern parts of Laurentia. Accompanying plates include a newly compiled map of the Precambrian rocks of the conterminous U.S., maps showing relationships of the Precambrian geology to magnetic anomalies and to isostatic residual gravity, and a new correlation chart for U.S. Precambrian rocks.