Abstract We present the results of 59 new apatite fission tracks (AFT), 24 new vitrinite reflectance analysis, and 154 new He thermocronometric analysis from the eastern flank of the Colombian eastern Cordillera at lat7° N to constrain the roles of plate tectonics, tectonic inheritance, and surface processes in building the Cocuy syntaxis. The Cocuy syntaxis is the region with the highest structural and topographic relief in the eastern Cordillera. The primary factor controlling that is faster tectonism, apparently related to the most important Panama collision at 4 Ma. This push from behind is focused between two resistant plates and escapes toward a weak foreland plate, which is able to flex. However, we document new Pliocene and younger AFT ages in the eastern side of the eastern Cordillera, which are related with focused and faster exhumation in the eastern flank. We suggest that this episode is responsible for the limited advance of the deformation front as basement-involved blocks. In addition, faster denudation causes faster sedimentation rates in the weak foreland plate east of the Cocuy syntaxis. In this case, the thick pile of Neogene synkinematic sediments would have limited thin skin deformation migration.

Abstract First–order lithospheric flexure, in response to discrete tectonic and sedimentary loads, controls basin–scale, base–level cycles in upstream deposits of retroarc continental foreland basins, in the absence of dynamic topography. A depositional sequence in this type of basin may be defined as a sedimentary succession formed during the adjustment of the fluvial systems to the equilibrium stage at or near base level. This sequence spans two accommodation episodes. The initial episode with high rates of subsidence corresponds to a thrust–loading period near the hinterland end of the elastic plate and may be identified by regional seismic–reflector onlap shifts from the foreland toward the hinterland. The second episode deepens and enhances the foreland flexure under the weight of the new sediment and may be identified seismically by a continuous onlap migration toward the foreland. A depositional cycle ends either when a period of nondeposition dominates the basin because the fluvial system attains the graded stage at or near base level or with the reactivation of thrusting activity, initiating a new cycle. Base level appears to control the top of the sedimentation boundary, but can adjust passively, during vertical movements caused by the regional isostatic compensation of the elastic plate. Regional paraconformities appear to represent periods of equilibrium of the depositional profile when the fluvial systems reach a graded stage and total tectonic quiescence. Seismic and well data from the northern–Andes, continental retroarc Putumayo foreland basin, in Colombia, are used to test the model for flexure induced, base–level cycles. Results suggest that onlap seismic facies migrating toward the foreland predominate during sediment–controlled flexural periods(on average, ~ 77 % of the total deflection), whereas onlap shifts from the foreland toward the hinterland mark those periods when thrust belt loads dominate flexure (on average, 23 % of the total deflection). The seismostratigraphic record exhibits as much as eight flexure–controlled Cenozoic sequences in the basin, in correspondence with an equal number of tectonic reactivation episodes. Geodynamically, the Putumayo foreland basin has been modeled to encompass a total added lithospheric deflection of asmuch as 450 km (279 mi) wide. During the Oligocene, the maximum subsidence rates reached approximately 150 m /y. ( ~ 492 ft/m.y.) and the maximum width of the effective tectonic load (a discrete part of the thrust belt) affecting the plate reached a value of approximately 30 km ( 20 mi). The geometry of the effective thrust belt and the wavelength of the lithospheric deflection modeled in this article preclude the need to invoke dynamic topography as a downward force acting on the plate and creating extra accommodation in the basin. The effective elastic thickness of the plate is 30 ± 10 km (19 ± 6 mi; and has not changed apparently since the early Paleocene). Each loading event, for instance, tectonic and sediment loads, produces a corresponding fore bulge whose location and dimensions change concomitant with the evolution of the basin.

Abstract The study draws from reflection seismic, in-situ stress and low-temperature geochronology data on the Eastern Cordillera–Llanos foreland basin system of Colombia, which is an example of the retro-wedge of the orogen with an advancing subduction zone. The system was obliquely converging during deposition of the Lower Oligocene–Lower Miocene Carbonera to recent Guayabo formations, recording it by the northeastward depocentre shift in the proximal Llanos Basin. While the southern portion of the foreland did not flex and undergo flexural normal faulting after Carbonera deposition, the northern portion did. The earthquake data indicate that the northern Eastern Cordillera undergoes strengthening by internal deformation, while the southern segment is already strong enough to undergo significant displacements dominantly along its bounding fault systems. Furthermore, the southern segment initiated detachment of the first thick-skin blocks from the proximal Llanos Basin. Such co-existence of different convergence maturity stages along the orogen strike allows unravelling of its development starting with internal deformation and foreland flexure, followed by mountain building and large-scale boundary fault displacements, to the large-scale foreland deformation. The onset of new foreland accretion seems to be controlled by the resistance of the foreland plate to flexing, given that the orogenic engine continues to drive convergence. Supplementary material: Discussion of evidences for dextral transpression in the Eastern Cordillera, data on exhumation history of the Eastern Cordillera and colour versions of Figures 4–6 are available at http://www.geolsoc.org.uk/SUP18629

Abstract The structure, stratigraphy and magmatic history of northern Peru, Ecuador and Colombia are only adequately explained by Pacific-origin models for the Caribbean Plate. Inter-American models for the origin of the Caribbean Plate cannot explain the contrasts between the Northern Andes and the Central Andes. Persistent large magnitude subduction, arc magmatism and compressional deformation typify the Central Andes, while the Northern Andes shows back-arc basin and passive margin formation followed by dextral oblique accretion of oceanic plateau basalt and island arc terranes with Caribbean affinity. Cretaceous separation between the Americas resulted in the development of a NNE-trending dextral–transpressive boundary between the Caribbean and northwestern South America, becoming more compressional when spreading in the Proto-Caribbean Seaway slowed towards the end of the Cretaceous. Dextral transpression started at 120–100 Ma, when the Caribbean Arc formed at the leading edge of the Caribbean Plate as a result of subduction zone polarity reversal at the site of the pre-existing Trans-American Arc, which had linked to Central America to South America in the vicinity of the present-day Peru–Ecuador border. Subsequent closure of the Andean Back-Arc Basin resulted in accretion of Caribbean terranes to western Colombia. Initiation of flat-slab subduction of the Caribbean Plate beneath Colombia at about 100 Ma is associated with limited magmatism, with no subsequent development of a magmatic arc. This was followed by northward-younging Maastrichtian to Eocene collision of the trailing edge Panama Arc. The triple junction where the Panama Arc joined the Peru–Chile trench was located west of present-day Ecuador as late as Eocene time, and the Talara, Tumbes and Manabi pull-apart basins directly relate to its northward migration. Features associated with the subduction of the Nazca Plate, such as active calc-alkaline volcanic arcs built on South American crust, only became established in Ecuador, and then Colombia, as the triple junction migrated to the north. Our model provides a comprehensive, regional and testable framework for analysing the as yet poorly understood collage of arc remnants, basement blocks and basins in the Northern Andes. Supplementary material: A detailed geological map is available at http://www.geolsoc.org.uk/SUP18364