Structural Significance and Analysis of Mid-Continent Gravity High

The Mid-Continent gravity high is a large gravity anomaly which extends from Lake Superior to Oklahoma, and occupies the center of a 300 mi-wide fault system which crosses the center of the North American continent. This basement feature can be related to Keweenawan faults and intrusives near Lake Superior. Throughout the Paleozoic Era movement continued along these faults, resulting in several anomalies that were mapped in Kansas, Nebraska, Iowa, and Minnesota. A new technique of gravity analysis involving the fitting of nonorthogonal polynomial surfaces to gravity data is particularly applicable to the study of basement geology as delineated by gravity measurements. The polynomial analysis shows a detailed correlation of the gravity residuals with both basement geology and Paleozoic structure. It is apparent that in the central United States this relationship of old zones of weakness to younger movement is the norm rather than the exception. Unfortunately, the lack of drill holes makes study of the basement geology difficult. This leaves the task to geophysical methods. The use of the computer and new techniques of analysis improve study efforts but it is only through a combination of the geophysical methods, computers, and all available geologic information that the most nearly accurate conclusion can be reached.