QUATERNARY FOLDING OF THE TAME ANTICLINE, LLANOS BASIN, COLOMBIAN ANDES

Along strike gradients in shortening rates in the Colombian Andes is thought to reflect the complex interaction between eastward flat slab subduction of the Nazca plate and normal southward subduction of the Caribbean plate. This interaction produces a northward increase in shortening rates that are reflected not only in the high seismicity of the Bucaramanga nest, but also in the recent deformation and advance of the thrust wedge at 6.5˚N latitude. The Tame anticline is a N15E trending fault propagation fold that is 6 km wide by 14 km long, and is actively growing due to slip on the east directed Cusiana fault. The kinematic evolution of the fold geometry is modeled based on seismic reflection data and slip rates are calculated using in situ terrestrial cosmogenic nuclide dating of warped and abandoned terraces along the east flowing antecedent Macaguana creek. Incision between the sampled terraces and present river elevations are 220 and 150 m. The abandonment ages are 93 kyr and 45 kyr, respectively, suggesting uplift rates of 1.8 to 3.5 mm/yr, respectively. Trishear kinematic modeling is used to reconstruct fold growth and provide a more rigorous calculation of recent shortening rates. A comparison with shortening rates obtained from global positioning system data provides an opportunity to investigate the dynamics of fold growth over various timescales for the northern Colombian Andes.