TECTONIC ANALYSIS OF NORTHWESTERN SOUTH AMERICA FROM INTEGRATED SATELLITE, AIRBORNE AND SURFACE POTENTIAL FIELD ANOMALIES

The effects of anomaly superposition and source ambiguity hinder tectonic interpretation of the North Andes gravity or magnetic anomalies. Strong positive Terrain Gravity Effects (TGE) and Free Air Gravity Anomalies (FAGA) suggest that the crust – mantle interface under the northwestern Andes may be too elevated to be isostatically compensated. Strong negative FAGA along western South America and the Greater and Lesser Antilles islands can reflect deeper mantle displaced by subducting oceanic plates. Terrain correlated FAGA (TCFAGA) and compensated terrain gravity effects (CTGE) map deep roots of thickened low density crust. Crustal thickness estimates for the North Andes ranging from about 30 km to 56 km conform well to regional seismic constraints. CHAMP satellite magnetic anomalies reveal a magnetic low oriented WSW-ENE over the Takatu Aulacogen. Magnetic anomalies at 20 km altitude of northwestern South America show an ESE-ENE positive anomaly at the western margin of the Guiana shield that may be related to crustal shallow features which are undetectable at higher satellite altitudes. A magnetic high located in the northern part of the Andes Mountains is associated with plutonic rocks intruding the uppermost continental crust. Joint 3D inverse modeling of the satellite, marine and terrestrial gravity and magnetic anomaly maps highlights crustal deformation from plate collision and subduction in Northwestern South America.