The structure of Colombia

Abstract

The geology of Colombia involves rock formations of Precambrian to Quaternary ages and their structure reflects all the complex evolutionary stages undergone in their development from the basement Guiana Shield in the east to the Tertiary Andean Cordilleras in the west.The Colombian Andes proper consist of five distinct and physiographically independent mountain ranges: the Coastal Range, Cordillera Occidental, Cordillera Central, Cordillera Oriental with its continuation, Cordillera de Perija, and the Sierra Nevada de Santa Marta. Each of these elements shows marked structural characteristics and is of different age of uplift. The Guiana Shield and its outliers in the eastern half of the country represent the old continental basement complex. The growth of the rest of Colombia took place west and north of the shield. The largest part of the shield area is covered with thin beds of Tertiary sediments and comparatively little is known of its structural development.The data available on the Colombian Andes permit an outline of the successive evolution and the structural relations of its component elements. Thus, it can be established that, as in the structure of the Venezuelan Andes, Sierra de Merida, to the northeast [Oppenheim, 1937] and the Ecuadorian Andes to the south [Oppenheim, 1950b], the predominating tectonic pattern of the Colombian Andes is that of block‐faulting and not of overthrusting. This distinctly Andean type of structure is further enhanced in Colombia by the dual constitution of the Colombian Cordilleras—the Western and Central Cordilleras being of predominantly igneous and metamorphic composition, while the eastern Cordillera Oriental is largely of sedimentary constitution [Oppenheim, 1947].The rise of the Cordilleras does not seem to be due to direct tangential pressures from east to west but, rather, to vertical stresses, or their components. The graben structure of the Magdalena and Cauca troughs and the absence of important regional zones of low‐angle thrusting or nappe structures in the Colombian Andes confirm this view.A hypothetic evolution of the Colombian Andes from island arcs appears suggestive and deserves further study, as it seems to confirm the existing geological and geophysical connections of the Cordilleras with island arcs of the Lesser Antilles, a relation that has been pointed out by Hess [1938], Oppenheim [1948], and Gutenberg and Richter [1949]