Tectonic Analysis of Northwestern South America from Satellite and Surface Magnetic Data

The proposed plate boundary zones among the North Andes microplate and the Caribbean, South American and Nazca plates involve the spatial distribution of oceanic and continental crust with contrasting magnetic properties. Using satellite and terrestrial magnetic data, we estimate the comprehensive crustal magnetic anomaly field for new constraints on the plate boundary crustal discontinuities. Removing the IGRF10 core field model up to degree 13 from CHAMP satellite magnetic anomalies at 2o intervals reveals a residual magnetic anomaly low oriented WSW-ENE that does not appear to be related to the known geological structures of the North Andes oriented SW-NE. This magnetic low is associated with the plate boundary zone between the Guiana shield and the North Andes microplate. The surface magnetic map of northwestern South America shows a different pattern in the distribution of magnetic anomalies. There is an ESE-ENE positive anomaly at the western part of the Guiana shield that may be related to shallow structures that are not detected at higher satellite altitudes. There is a magnetic high located in the northern part of the Andes Mountains that is associated with plutonic rocks that have reached shallow positions affecting the uppermost continental crust. Joint 3D inverse modeling of the satellite and terrestrial anomaly maps greatly facilitates the geological interpretation of the tectonically complex study region