Abstract

Across much of North America, the contact between Precambrian basement and Paleozoic strata is the Great Unconformity, a surface that represents a >0.4 b.y.-long hiatus. A digital elevation model (DEM) of this surface visually highlights regional-scale variability in the character of basement topography across the United States cratonic platform. Specifically, it delineates Phanerozoic tectonic domains, each characterized by a distinct structural wavelength (horizontal distance between adjacent highs) and/or structural amplitude (vertical distance between adjacent lows and highs). The largest domain, the Midcontinent domain, includes long-wavelength epeirogenic basins and domes, as well as fault-controlled steps. The pronounced change in land-surface elevation at the Rocky Mountain Front coincides with the western edge of the Midcontinent domain on the basement DEM. In the Rocky Mountain and Colorado Plateau domains, west of the Rocky Mountain Front, structural wavelength is significantly shorter and structural amplitude significantly higher than in the Midcontinent domain. The Bordering Basins domain outlines the southern and eastern edges of the Midcontinent domain. As emphasized by the basement DEM, several kilometers of structural relief occur across the boundary between these two domains, even though this boundary does not stand out on ground-surface topography. A plot of epicenters on the basement DEM supports models associating intraplate seismicity with the Midcontinent domain edge. Notably, certain changes in crustal thickness also coincide with distinct changes in basement depth.

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