THE ROLE OF THE CHOCÓ-PANAMA ARC COLLISION ON THE LATE CENOZOIC ACCRETIONARY OROGENESIS OF THE NORTHERN ANDES

O papel da colisão do Arco Chocó-Panamá na orogênese acrecionária do Cenozoico Tardio dos Andes do Norte

Abstract

The collision of the Chocó-Panama Arc is the most voluminous process of continental growth by addition of exotic material to the western margin of South America in the Neogene. The distribution of morphotectonic features, Bouguer anomalies, estimations of surface erosion, earthquake and GPS data, and geodynamic indicators of crustal deformation, were used to determine the effects of the ongoing indentation. A strong negative observed Bouguer anomaly between the Central Cordillera and western border of the Eastern Cordillera, as compared to the calculated anomaly, indicates overcompensation. The maximum deflection of the late Cenozoic accretionary orogen during its widening phase could occur due to the effect of flexural loading of the Western and Central cordilleras. To overcome the overcompensation, a mass excess corresponding to a thick, deforming succession of a former sedimentary basin must be removed. Erosion can partially achieve this, which may also account for the anomalously high sediment fluxes from the Eastern Cordillera to the lowlands of the Magdalena and Orinoco megafluvial systems. The maximum width of the deforming zone indicates that the surrounding regions of the indenter have already attained their maximum height threshold. Consequently, horizontally transferred forces further east uplifted and thickened adjacent areas, such as the Eastern Cordillera, which experienced a late Cenozoic climax of growth to its present-day configuration. The occurrence of two clusters of shallow-to-intermediate earthquakes, one situated to the south and another to the north of the indenter boundary, provides evidence of strain localization. Dynamic feedback between surface and climatic processes and crustal deformation, contributes to a scenario of “mountain growth” that opposes the tendency of the system to be dynamically unstable and experience collapse.