Bouguer images of the North American craton and its structural evolution

Abstract

Processing of existing gravity and aeromagnetic data with modern methods is providing new insights into crustal and mantle structures for large parts of the United States and Canada^1–3. More than three-quarters of a million ground station readings of gravity are now available for this region. These data offer a wealth of information on crustal and mantle structures when reduced and displayed as Bouguer anomalies, where lateral variations are controlled by the size, shape and densities of underlying materials. We have used digital image processing techniques to generate Bouguer images that display more of the granularity inherent in the data as compared with existing contour maps. A dominant NW–SE linear trend of highs and lows can be seen extending from South Dakota, through Nebraska, and into Missouri (Fig. 2). The structural trend cuts across the major Precambrian boundary in Missouri, separating younger granites and rhyolites from older sheared granites and gneisses. This trend is probably related to features created during an early and perhaps initial episode of crustal assembly by collisional processes. The younger granitic materials are probably a thin cover over an older crust.