The eastern foothills of the Eastern Cordillera of Colombia: An example of multiple factors controlling structural styles and active tectonics

We decipher the geometry, timing, and kinematics of deformation of a region in the eastern foothills of the Eastern Cordillera of Colombia. We assess the influence of inherited structural fabrics, changes in basin geometry, erosional denudation, and the characteristics of the tectonic stress field with respect to the evolution of the structural styles of the deformation front in the Eastern Cordillera. Detailed structural and geomorphic mapping of an area of similar to 5000 km(2), analysis of seismic-reflection profiles, cross-section balancing, tectonic stress-field indicators, and new apatite fission-track data are used to characterize the partitioning of Late Cenozoic deformation in the eastern foothills of the Eastern Cordillera of Colombia. During the late Miocene-Pliocene, in the Eastern Cordillera, deformation migrated from inverted master normal faults to low-elevation, low-amplitude structures in the foreland. However, this shift in the locus of deformation was not spatially uniform. The deformation front is wider in a northern sector of the Cordilleran foothills, where sedimentary units are thicker, and shortening is perpendicular to the structures. This shortening direction is identical to the direction of the greatest horizontal stress S-Hmax as seen in borehole breakouts. During the late Miocene-Pliocene, basement ranges are passively uplifted by younger, more frontal thrusts. The eastern foothills of the Eastern Cordillera thus reveal a complex combination of factors responsible for the structural styles and partitioning of active deformation in an inversion orogen. Over time, the most important factor changes, from the role of inherited structural fabrics to the geometries of basin fills.