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Geophysical Diagnosis of Mid-Continent Rift

Albert B. Dickas

Of all recognized rift systems, the Mid-Continent rift may be the most geophysically analyzed of its genre. The data base associated with this 1,900-km (1,180-mi) long plate tectonic feature is evenly distributed between gravity, magnetics, and seismology. Since 1983, the western arm of the rift, traced from northeastern Kansas into the Lake Superior basin, has become an oil and gas exploration frontier. The target source and reservoir rocks are of Proterozoic Y (middle Keweenawan) age (1,047 ± 35 Ma minimum). Associated sedimentary and igneous rocks crop out only in northwestern Wisconsin and the adjacent upper peninsula of Michigan.

Workers have developed various geophysical models for the Mid-Continent rift, and with the advent of economic interest, the classical compressive, central horst model has been questioned.

Geophysical diagnosis of the Mid-Continent rift has gone through three stages. In stage I (late 1930s to 1978), the rift was discovered and identified, and its basic outline, geographic extent, and preliminary structural model were developed. In stage II (1978-1981), the Consortium for Continental Reflection Profiling conducted surveys in Kansas and Michigan, which suggested the rift was an extensional, subsiding trough. Now, in stage III (1984 to present), reflection seismology studies along the entire western area of the rift permit a new review. Examples of industrially acquired lines will be presented.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.