Three-dimensional structure and kinematics of the Piedras-Girardot foldbelt in the northern Andes of Colombia

Detailed geologic mapping, strain analysis, and simple stratigraphic principles indicate that deformation in the Piedras-Girardot foldbelt in the northern Andes began in the early Campanian with incipient propagation of faults that uplifted gentle domes where the accumulation of some sandy units did not take place. Maastrichtian unroofing of a metamorphic terrane west of the Piedras-Girardot foldbelt is documented by a conglomerate that was deformed shortly after deposition developing a conspicuous intragranular fabric of microscopic veins that accommodate little extension (between 1 and 2 percent in a general northeast-southwest direction). This extensional fabric, distortion of fossil molds, and a moderate cleavage most likely developed concurrently, during and after incipient late Cretaceous folding, but before large scale Paleogene faulting and folding. Cleavage also seems to record small amounts of contraction in a general northwest-southeast direction. Paleogene folding and thrust sheet propagation is recorded by syntectonic strata, and records westward to southwestward propagation of faults. Mesoscopic fabric elements associated with continuous Paleogene deformation are nearly absent, and apparently were passively rotated and translated along thrust sheets. Neogene deformation took place only in the norhtwestern flank of this foldbelt. As a result of this history of deformation, a complex array of faults and folds exists: northwest- and west-verging thrust faults, north- and northeastverging normal faults, and north- and northeast-trending strike-slip faults. Changes in the structural trend delineate a sigmoidal sinistral stepover in this dextral system, with faults verging outwardly in opposite directions defining a positive flower structure.