A pair of oppositely dipping, crustal-scale shear zones imaged within Grenville basement beneath the Paleozoic cover of Ohio can be correlated, via geopotential lineaments, with similarly oriented geologic and seismically imaged structures hundreds of kilometres to the northeast and southwest, suggesting a relatively simple structural framework for the eastern midcontinent region. An east-dipping zone extending from Lake Huron through western Ohio, and possibly farther southwest, marks the western edge of the Grenville province. Perhaps of greater consequence to an understanding of Grenville tectonics is the discovery of a west-dipping zone underlying the Appalachian basin from northern Alabama to New York within the Grenville province. Correlation of this feature with the seismogenic Clarendon-Linden fault in western New York and a boundary between terranes containing magmatic-arc rocks exposed in Canada suggests that it could mark the site of an intra-Grenville province suture zone. Implications of this interpretation are that the Precambrian foundation of the eastern U.S. midcontinent comprises a relatively simple assemblage of laterally extensive terranes or belts of coeval terranes accreted by familiar plate tectonic processes, and that deep seismic profiling is an effective tool for mapping the three-dimensional distribution of these terranes.