Abstract The geometry, kinematics and evolution of thick- and thin-skinned fold and thrust-belts have been characterized for many tectonic provinces. However, the impact of prior extension in the structural evolution of fold and thrust-belts remains under-appreciated. We use a series of balanced cross sections across areas of thin- and thick-skinned tectonics superimposed over former extensional structures in order to characterize the style of deformation, segmentation and displacement magnitude. We detect the style of fault linkage in foothill settings adjacent to inversion belts. The most relevant aspect is the presence of inherited ‘soft linkages’ generating zones of displacement deficit, which in contraction interact laterally with en-echelon inverted segments via ‘detachment linkages’. We document the temporal development and interaction between inverted faults and fault splays branching from them where both are coeval but where the frontal fault tips propagate more slowly during Oligocene and Early Miocene times. Later, during the Neogene, the frontal fault splays slip faster than the main inversion fault. The structural style of thrust-belt development displays along-strike variations, which reflect the changes in sedimentation rates and mechanical conditions of deformation. However, the timing and magnitude of shortening remain uniform along-strike.

Abstract We use the Eastern Cordillera of Colombia as an example in early stages of inversion orogen showing still modest values of shortening. The style of deformation recorded in this orogenic chain seems to be strongly influenced by two main factors. The first is the pre-compression geometry of the rift basin, conditioning the strong heterogeneity imparted by a trough filled with Jurassic to Neocomian sediments limited by Precambrian and Palaeozoic high-angle walls. The second factor is the orientation of the stress regime with respect to the main normal faults during the inversion. If the stress field is of pure compression, the normal faults are not extensively inverted and the deformation is accommodated mainly in terms of footwall shortcuts. On the other hand, in transpressive regimes the inversion of the former normal faults is more common and the footwall shortcuts are not dominant structures. No significant lateral variations in tectonic shortening are found in the Eastern Cordillera. Finally we emphasize the role of buckle folds in the internal parts of the inversion orogens and give a cautionary note when interpreting these structures in terms of fault-related folding using the well-documented example of the Soapaga fault area.

Abstract Geologic maps, seismic profiles, and structural field data are used to constrain a structural cross section of the eastern Cordillera of Colombia, the Medina–Utica transect, from the Llanos to the middle Magdalena Valley forelands. The Medina–Utica transect illustrates the geometry and kinematic evolution of a continental back-arc region that evolved from rifting to compressional mountain building because of changes in the dynamics of the subduction zones nearby. As other orogens formed by rift inversion, the eastern Cordillera shows intense thrust deformation in the foothill margins, associated with the reactivation of the main former extensional margins, and an orogen interior with comparatively less deformation and relief (the Sabana de Bogota Plateau). While the orogen margins are dominated by basement-involved thick-skinned thrusting, the Sabana de Bogota is interpreted as a salt-detached fold belt with a basal decollement in lower Cretaceous evaporite at a depth of ca 4 km (2.4 mi). Anticlines in the Sabana de Bogota are interpreted to have formed as diapiric salt walls during the pre-orogenic rifting, later squeezed and welded during the Andean shortening, together with syntectonic sedimentation and halokinetic sequence development. A sequential restoration of the cross section to selected time steps based on a wealth of tectonics-sedimentation and thermochronological data enables to track the evolution of orogenic deformation. The total shortening in the Medina–Utica transect is calculated as 82 km (50.9 mi) (27% of the predeformed length). Compressional deformation in the area started probably near the Cretaceous-Tertiary boundary, manifested by localized folding and faulting in the Sabana de Bogota and foothills, much guided by the weak salt horizons. Evidence for gentle folding and thrusting persists through the Paleogene at low rates of <0.5 mm/a. By the Neogene the mountain belt was in full accretion, and rapid shortening at rates near 3 mm/a was accommodated by thrusting in the outer margins of the former rift system. The eastern Cordillera of Colombia exemplifies a pattern of tectonic evolution of inverted rifts in which deformation commences in the basin interiors in a distributed way, strongly controlled by weak stratigraphic units, and evolves to a point when intense shortening is shifted into the weak faults at the rift margins. This gives rise to prominent mountain topography, rapid erosion, and fast sedimentation in the forelands.

Abstract The Northern Andes of Colombia is a key locality for understanding tectonic inversion of symmetric rifts. A review of available data on structural geometry and deformation timing, and new thermochronology and provenance data from selected localities, enable the construction of balanced cross-sections and shortening budgets. During early deformation in the Palaeocene, most shortening was focused in the western sector of the orogen, in the Central Cordillera and the Magdallena Valley, although widely spaced and mild inversion occur in areas as far to the east as the Llanos Basin. After a period of tectonic quiescence in the Middle Eocene, deformation resumed across a former early Mesozoic graben in the Eastern Cordillera. Peak shortening rates and out-of-sequence reactivation of the main inversion faults were in place in latest Miocene time, during a phase of topographical growth. Our results indicate that coeval activation of basement highs and adjacent slower-slip shortcuts appear to be characteristic of inverted symmetric grabens. However, before reactivation and brittle faulting occur, strain hardening is required. Deformation rates in the Eastern Cordillera correlate with the westwards velocity of the South American Plate. A threshold convergence rate of approximately 2 cm year −1 seems to be necessary to activate shortening in the upper plate.