Regional North American gravity and magnetic anomaly correlations

Abstract

Summary. Correlation of gravity and magnetic anomalies combined with other geological and geophysical data is useful for enhancing the quality of geological interpretation of potential anomaly fields. Maps produced by equivalent point source inversion are used to investigate visual-spatial correlations of surface free-air gravity and POGO satellite magnetic anomalies and regional heat flow and tectonic data for North America and adjacent marine areas. A quantitative analysis of regional potential field anomaly correlations at satellite elevations is also considered utilizing Poisson’s theorem in a moving-window linear regression between derivatives of the anomalous gravity and magnetic fields. An inverse relationship is observed between long-wavelength gravity and magnetic anomalies over continental terrain. Negative gravity and positive magnetic anomalies are areas characterized by relatively thick crust and high magnetization. An example is a prominent magnetic high which corresponds to a trend of gravity minima extending from the Anadarko Basin to the Cincinnati Arch. Negative magnetic and positive gravity anomalies characterize thinner crust and regions of higher heat flow such as the Cordillera of North and Central America and specifically the Yellowstone geothermal region. Although gravity and magnetic anomalies over oceanic areas show poor correlation, the sign of the statistical correlation generally is positive. 1 Crustal correlation considerations The utility of long-wavelength gravity anomalies, covering several degrees of surface area, for geological analysis is well recognized. Magnetic anomalies which have significant energy in wavelengths of several hundred kilometres also have been identified as originating from within the Earth’s crust and perhaps the uppermost mantle. The geological interpretation of these regional anomalies is hindered by the effect of anomaly superposition and source ambiguity which is inherent to the analysis of potential fields. An approach to minimizing these limitations, especially in continental terrains, is to evaluate the correlation between anomalous gravity and magnetic fields. The basis of correlation analysis is the hypothesis, commonly validated in continental areas, that variations in lithology and physical properties of the crystalline crust are reflected