KGS Geophysics in Kansas Original published in D. W. Steeples, ed., 1989, Geophysics in Kansas: Kansas Geological Survey, Bulletin 226, pp. 215-228

Geophysical model of the Midcontinent Geophysical Anomaly in northeastern Kansas

by Chaturong Somanas, Ralph W. Knapp, Harold L. Yarger, and Don W. Steeples

Kansas Geological Survey
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A geophysical model of the Midcontinent Geophysical Anomaly (MGA) in northeastern Kansas was derived to fit gravity and magnetic data using an initial model suggested from COCORP seismic sections, along with available drill data. An asymmetric basin filled with interbedded basaltic and clastic rocks in the shallow crust, interpreted by Serpa et al. (1984), appears to be mainly responsible for the primary positive magnetic anomaly of the MGA. The favorable magnetization of 60° inclination and 320° declination indicates that the remanent magnetization is an important factor. Reprocessing part of COCORP seismic data reveals a possible mafic intrusion in the shallow crust beneath a secondary magnetic high. Its favorable net magnetization of 30° inclination and 80° declination suggests it occurred in a different ambient earth's magnetic field than that in which the basaltic rift basin was formed. In addition, the nonmagnetic source of high density at midcrustal levels extending to deep crust and the nonmagnetic Rice Formation basins of low density at shallow crust on both sides of the MGA were proposed to fit the gravity anomaly. The final derived model infers the mafic intrusion in the shallow crust beneath the secondary magnetic high to be of younger age than the Rice Formation.

Kansas Geological Survey
Comments to
Web version Oct. 16, 2013. Original publication date 1989.