Abstract: Fold and Thrust Belt Along the Western Flank of the Eastern Cordillera of Colombia: Style, Kinematics and Timing Constraints Derived >From Seismic Data and Detailed Surface Mapping 

Abstract

The Eastern Cordillera of Colombia is considered to be the result of compression and uplift during the late Miocene–Pliocene Andean orogeny. Nevertheless, detailed mapping carried out on a portion of the fold belt exposed along the western flank of the Eastern Cordillera suggests that deformation began in late Paleocene–early Eocene time, in the form of a west-vergent, forward-propagating fold-and-thrust belt. Several structures related to this event remain concealed beneath the late Paleocene–late Eocene unconformity, and synkinematic sediments are preserved locally within some of these thrust sheets. The relief generated during this deformational episode constrained the depositional axis of late Eocene fluvial sediments to run along the present-day crestal zone of the Eastern Cordillera. Onlapping basal Miocene molassic sediments on tilted middle Miocene fluvial deposits suggest that a series of seismically delineated intercutaneous wedges located at the thrust front formed in late Miocene time. These structures mark the onset of the Andean deformational episode. Thrusting polarity reversed during the latter event, that is, toward the hinterland, and Paleogene structures were reactivated. Additionally, the late Paleocene–early Eocene unconformity surface was folded and incorporated into north-plunging folds, and Cretaceous extensional faults were inverted. As a result, the Eastern Cordillera developed its present pop-up, doubly vergent fold-belt geometry, flanked by thick molassic sequences that document the Miocene–Pliocene Andean orogeny. Regionally, the latest Campanian–Maastrichtian uplift of the Central Cordillera, Paleocene–early Eocene thrusting in the Middle Magdalena Valley and along the western flank of the Eastern Cordillera, and ultimately inversion and major uplift of the entire Eastern Cordillera in late Miocene–Pliocene time, attests to the eastward propagation of deformation from the Central toward the Eastern Cordillera. Kinematically, the driving element of deformation would have been the obliquely accreting western terranes of the Central and Western Cordilleras and the Panama arc. These transferred their easterly component of convergence to the Eastern Cordillera through a basal intracrustal detachment.