NATURE OF THE BASEMENT OF THE SOUTHERN COLOMBIAN CARIBBEAN MARGIN

The nature of basement of the Southern Colombian Caribbean Margin is still controversial due to the lack of compositional information related with the basement of the San Jacinto fold Belt. Previous models based on gravimetric data defined a location for the major boundary between continental and oceanic crust. However none of these models has deal with the internal structures of the basement in the oceanic or in the continental crust. In this study we compiled petrological data from oil exploratory wells to define major compositional groups. Additionally, we used published magnetic anomaly and structural maps to infer the extent of major bodies within the basement, and compare them with geologic maps, identifying major structural provinces. The oceanic basement is composed of gabbros, peridotites, and sediments with interbedded basalt. The continental basement is composed of schist and phyllite with intrusions of plutonic rocks in the San Jorge Basin and the Maguangue High and intrusion of volcanic rocks in the San Jorge Basin. A comparison of radiometric ages of the basement of the Lower Magdalena Basin with the metamorphic and magmatic belts of the Sierra Nevada de Santa Marta, suggest a continuous province. Our results show that the Romeral Fault System constitutes the boundary between continental and oceanic crust, at least at a shallow level of the crust, whereas the Sinu lineament represent no change in composition in the basement, even though it is a major structural feature.