Origin and Kinematics of Extension in the Llanos Basin, Colombia

s. However the origin and kinematics of these faults have received little attention. Our preliminary analysis indicates that these faults are related to brittle deformation of the lithosphere, as a response of a rapid onset of tectonic loads in the growing Eastern Cordillera during Late Miocene to recent times. The magnitude of extension decreases eastward, as the distance from the thrusting front increase, ranging from hundreds of feet in the Upia area to tenths of feet in the Sabanero – Rubiales area. Timing of fault initiation and activity are constrained based on recent thermochronological data from the Eastern Cordillera, that shows an abrupt increase in shortening, from 1.5 – 1.8 mm/yr during the Upper Miocene (~2 Ma ago) to 3.5 – 5.0 mm/yr for the Plio-Pleistocene (2 Ma ago), and also from regional correlations with published biostraigraphic data of the basin. The deformation style of the northern portion of the Llanos basin is compared with the foreland basins of Putumayo (Colombia) and Oriente (Ecuador), where the trapping mechanism, rheology of the crust and basin fill are strikingly different, leading us to conclude that these basins represents two different tectonic provinces, that are being sutured by the north-eastern extension of the Algeciras - Guayaquil fault system, that extends into the Llanos basin transferring slip from the trench inboard.