No abstract

A combination of new surface and subsurface structural data, new stratigraphic data on conventional provenance, facies and palaeocurrents, low-temperature thermochronology and detrital zircon U–Pb provenance data provides a comprehensive account of the timing of deformation in the intermountane Middle Magdalena basin of the Central Colombian Andes, and allows evaluation of the style of foreland basin deformation associated with tectonic inversion. This robust dataset enabled documentation of focused tectonic activity in two competing low-relief basement structures to the east and west of the present Middle Magdalena Valley during the Palaeogene, earlier than previously recognized. Cenozoic sediment accumulation of a sedimentary pile up to 7 km thick in the Middle Magdalena Basin created a large original taper angle in this part of the north Andes. At that time, when the detachment rocks were deeply buried, the original larger taper angle facilitated the forelandward advance of deformation instead of promoting its stagnation.Supplementary material:Raw data results from geochronometrial analyses are available at: http://www.geolsoc.org.uk/SUP18627

The initial stages of tectonic inversion and the mechanisms of selective reactivation and abandonment of pre-existing normal faults during contractional orogenesis are explored in a partially buried Cenozoic thrust belt in the Andes of Colombia. A multidisciplinary approach that includes subsurface structural mapping, multimethod thermochronometry and detrital zircon U–Pb geochronology reveals the extent of a Palaeogene thrust belt buried underneath the Cenozoic strata of the Middle Magdalena Valley Basin. A less oblique orientation with respect to compressive stress and shorter traces in faults of the Middle Magdalena Valley Basin with respect to faults in the western part of the Eastern Cordillera, apparently acted as deformation inhibitors of the Magdalena faults in advanced Neogene stages of inversion. Protracted Cenozoic eastwards tilting of the Central Cordillera and the tectonic load from the uplifting Eastern Cordillera favoured the accumulation of a thick Cenozoic sedimentary sequence in an, at least episodically, closed basin. All the above-mentioned conditions helped to block deformation in the Magdalena Basin, favouring deformation to be taken up by structures in the western Eastern Cordillera. These relationships underscore the importance of buried structural records in elevated hinterland basins, in which the low-relief stratigraphic cover overlies a complex subsurface record, potentially including large magnitudes of deformation during early orogenesis.Supplementary material:Tables and figures on the laboratory methods for the thermochronometrical and geochronometrical analyses are available at http://www.geolsoc.org.uk/SUP18601.

The Magdalena Valley fold-and-thrust belt is a tectonic province associated with inverted rift zones. This belt displays a narrow and discontinuous deformation front indicating association with inversion tectonics. We show the differences with an analogue belt on the eastern side of the Eastern Cordillera (Llanos foothills). To do that we use structural data (seismic, wells and geological maps) which characterize different structural geometries as well as palaeocurrents, provenance and thermochronology to analyse the timing of deformation. The new datasets allowed us to detect that inversion is limited whenever the stresses are more orthogonal to the rift structures, whereas the mountain front is more segmented in comparison to the Eastern Foothills because of the absence of a continuous low basal friction detachment horizon and a pronounced eastwards basement dip. These two factors favoured fault hard linkage. It is remarkable that, in spite of the distinct segmentation, all the different segments in the Magdalena belt are coeval.Supplementary material:U–Pb Zircon data are available at: http://www.geolsoc.org.uk/SUP18630.

No abstract