Onset of fault reactivation in the Eastern Cordillera of Colombia and proximal Llanos Basin; response to Caribbean–South American convergence in early Palaeogene time
The inversion of Mesozoic extensional structures in the Northern Andes has controlled the location of syn-orogenic successions and the dispersal of detritus since latest Maastrichtian time. Our results are supported by detailed geological mapping, integrated provenance (petrography, heavy minerals, geochronology) analysis and chronostratigraphical correlation (palynological and geochronology data) of 13 areas with Palaeogene strata across the central segment of the Eastern Cordillera. Spatial and temporal variation of sedimentation rates and provenance data indicate that mechanisms driving the location of marginal and intraplate uplifts and tectonic subsidence vary among syn-orogenic depocentres. In the late Maastrichtian–mid-Palaeocene time, crustal tilting of the Central Cordillera favoured reverse reactivation of the western border of the former extensional Cretaceous basin. The hanging wall of the reactivated fault separated two depocentres: a western depocentre (in the Magdalena Valley) and an eastern depocentre (presently along the axial zone of the Eastern Cordillera, Llanos foothills and Llanos Basin). In late Palaeocene–early Eocene time, as eastern subduction of the Caribbean Plate and intraplate magmatics advanced eastwards, reactivation of older structures migrated eastwards up to the Llanos Basin and disrupted the eastern depocentre. In early Eocene time, these three depocentres were separated by two low-amplitude uplifts that exposed dominantly Cretaceous sedimentary cover. Syn-orogenic detrital sediments supplied from the eastwards-tilted Central Cordillera reached areas of the axial domain of the Eastern Cordillera, whereas unstable metamorphic and sedimentary fragments recorded in the easternmost depocentre were supplied by basement-cored uplifts with Cretaceous and Palaeozoic sedimentary cover reported in the southern Llanos Basin. This tectonic configuration of low-amplitude uplifts separating intraplate syn-orogenic depocentres and intraplate magmatic activity in Palaeocene time was primary controlled by subduction of the Caribbean Plate.