SPECTRAL ANALYSIS OF GRAVITY DATA WITHIN THE NORTH-CENTRAL USA

Newly compiled gravity data within the north-central United States was used to investigate the crustal structure of the region's Precambrian geology. Spectral analysis of the gravity data was used to compliment other interpretational techniques e.g., wavelength filtering and enhanced horizontal gradients that helped to delineate the gravity field characteristics of each of the Precambrian orogens. Power spectra were calculated along fourteen profiles of at least 100 km in length were analyzed throughout the study area. Along each profile at least three density interfaces and sometimes four were determined. The three major boundaries include the Phanerozoic sedimentary/basement, lower/upper crust and lower crust/upper mantle. Two regions of obviously thicker crust were determined: 1) west-central Dakotas/Nebraska and the eastern Dakotas. The crust in these regions were between 50 and 55 km thick. The western Dakotas/Nebraska thicker crust/lithosphere in general corresponds to the eastern boundary of the Trans-Hudson orogen and suggests that it extends into Nebraska. The eastern Dakotas are part of the Superior Craton and this region seems to have a thicker crust that the surrounding craton. This analysis expanded on the previous regional investigations by suggesting that several subterranes or crustal blocks may exist in each of the known orogens.