INTERPRETATION AND MODELING OF REGIONAL CRUSTAL STRUCTURE OF THE SOUTHEASTERN UNITED STATES USING RAW AND FILTERED CONVENTIONAL AND SATELLITE GRAVITY AND MAGNETIC DATA (MAGSAT, SEASAT, SPATIAL FILTERING)

In this study a methodology is developed for constructing crustal density and magnetic susceptibility models based on the interpretation of gravity and magnetic data. Potential field data over the southeastern United States have been filtered to enhance signals associated with sources tens to hundreds of kilometers in lateral extent. The procedure presented in this paper includes five steps. Constraining geological, geochemical, and additional geophysical information are compiled for the study area. A suite of lowpass filters is applied to regional potential field data. Qualitative interpretations are performed for target anomalies, using the long wavelength information present in the filtered maps together with constraining data. Quantitative modeling is performed.;Results of modeling on two scales, local/regional (less than 300 kilometers in lateral extent), and large-scale regional (greater than 300 kilometers) provide new insights into the nature of crustal structure and evolution in Georgia and the southern Appalachians. Southern Georgia crustal structure includes coincident upper crustal sources of short wavelength gravity and magnetic anomalies. The lower crust is marked by a broad zone of low magnetic susceptibility and high density contrast, giving rise to a long wavelength negative magnetic anomaly and a positive gravity anomaly. These structures are associated with the proposed Mesozoic South Georgia Rift.;The southern Appalachian magnetization model indicates a five-block, two-layer crustal magnetization structure. The upper crustal sources are associated with individual terranes which were accreted during Paleozoic time. Additional sources of gravity anomalies (including the Appalachian Basin) must be added to the model in order to explain the long wavelength gravity signature.;The quality of satellite magnetic and satellite-derived gravity data has been examined along with their suitability for modeling regional, long wavelength crustal properties. Gravity data derived from the Seasat mission compare favorably with coarsely sampled shipborne data for anomalies greater than 100 kilometers wavelength. These data can be used for modeling regional density structure of study areas in the open ocean. Magsat satellite data over the continental United States have much poorer resolution. These data are suitable only for very broad scale (400 kilometers anomaly resolution) modeling of crustal properties.