Regional magnetic and gravity anomalies of South America

Abstract

Preliminary satellite scalar magnetic anomaly data (MAGSAT) reduced to vertical polarization and long‐wavelength‐pass filtered free‐air gravity anomaly data of South and Central America are compared to major tectonic features. A number of correlations are observed, but these must be generalized because of the preliminary nature of the geophysical data and the inherent petrophysical variations within tectonic features. Statistical analysis of the magnetic data reveals that South and Central America are more magnetic and magnetically more variable than adjacent marine areas. More obvious correlations exist between magnetic anomalies and tectonic elements of the continents than in the case of oceanic areas. No obvious correlations occur between the tectonic features of the Atlantic Ocean, including the Mid‐Atlantic Ridge, and magnetic anomalies. The continental shields generally are more magnetic than adjacent basins, oceans and orogenic belts. In contrast, the major aulacogens are characterized by negative magnetic anomalies. Positive free‐air gravity anomalies are related to the Andean Foldbelt, but the relationship of this feature to magnetic anomalies is much less obvious. However, along the west coast of South America, the magnetic anomalies of the Pacific Ocean are separated from those of the eastern platforms by north to northwest trending anomalies. South of the equator along the Foldbelt, gravity maxima are related to magnetic minima, a relationship analogous to the situation observed in the Rocky Mountain Cordillera. North of the equator in Columbia, gravity and magnetic maxima roughly correlate along the Foldbelt.