Structural signatures of the Amazonian Craton in eastern Colombia from gravity and magnetometry data interpretation

Abstract Geophysical interpretation of potential field data plays an important role in the integration of geological data. Estimation of density and magnetic susceptibility variations within the upper crust helps evaluating the continuity of geological structures in the field. In the present study we use gravity and magnetic data in NW Amazonian Craton in Colombia. Total horizontal gradient of the reduction to magnetic pole were used to delineate magnetic lineaments and domains showing four zones, each with its own features. Multiscale edge detection (worming) of the data help delineate upper crustal structures that we interpret as tectonic boundaries that correlate with the four zones identified. 3D density and magnetic susceptibility inversion showed high density and/or high magnetic susceptibility sources correlated with these crustal structures. Zone (1) is located south of the Guaviare River, with predominant NW-SE and NE-SW magnetic lineaments; zone (2), located from south of the Guaviare River to the north, present nearly E-W magnetic lineaments and a deep E-W edge interpreted as a possible shear zone parallel to Guaviare, Orinoco and Ventuari rivers; zone (3) from south of the Vichada River to the north, with NE-SW and NW-SE lineaments; N-S zone (4) cuts the zones (2) and (3), characterized by high density/magnetic susceptibility source bounded by N-S deep edges. A more complete tectonic evolution interpretation requires further work, but we speculate that the zone (4) could indicate an aborted rift/collision suture and that the zone (2) is indicative of a younger deformation event. Shear direction at (2) is not clear: geological maps show NEE-SWW right-lateral faulting, but geophysical anomalies suggest left-lateral displacement, highlighted by left dislocation of the Orinoco River. We also speculate that a N-S edge located at the SE of the area can be related with the Atabapo Belt and the limit of Ventuari-Tapajos and Rionegro geochronological provinces.