Geophysical Model from Potential-field Data in Montgomery County, Kansas

Abstract

Potential-field data (gravity and aeromagnetic data with precision of 0.1 mGal and 3 nT, respectively) are inverted into density/magnetization distribution in the Precambrian basement of Montgomery County, Kansas, by a method of the iterative forward modeling of Xia and Sprowl (1992). The depth to the top of the Precambrian layer is determined by well data. The thickness of the layer is determined by trial-and-error such that the calculated density/magnetization models show reasonable correspondence with known geology. The inverted models agree with observed data to the root-mean-square error and the maximum deviation of 0.16 mGal and 1.4 mGal, respectively for gravity data, and of 5.3 nT and 18.8 nT, respectively, for magnetic data. The observed anomalies have been topographically corrected (for gravity data) and separated from the original anomaly (for gravity and magnetic data). The anomalies used for the inversion are obtained after subtracting the original anomaly's contribution by the subsurface terrane, which is modeled by well data. The inverted results show distribution of higher-than-average density/magnetization in the southwestern basement rock of the county, possibly due to an intrusion of granodiorite containing more than 3% of magnetite.