Quantifying Quaternary Deformation in the Eastern Cordillera of the Colombian Andes Using Cosmogenic Nuclide Geochronology and Fluvial Geomorphology

Abstract:

Northwest South America is actively deforming through the interaction between the Nazca, South American, and Caribbean plates. Though the Colombian Andes are well studied, much uncertainty remains in the rate of Quaternary deformation along the east directed frontal thrust faults hundreds of kilometers in board from the subduction zones. The eastern foothills of the Eastern Cordillera (EC) preserve deformed landforms, allowing us to quantify incision rates. Using ¹⁰Be in-situ terrestrial cosmogenic nuclide (TCN) geochronology, we dated 2 deformed fluvial terraces in the hanging wall of the Guaicaramo thrust fault. From the ¹⁰Be concentration and terrace profile relative to local base level, we calculated incision rates. We present a reconstructed slip history of the Guaicaramo thrust fault and its Quaternary slip rate. Furthermore, to quantify the regional Quaternary deformation, we look at the fluvial response to tectonic uplift. Approximately 20 streams along the eastern foothills of the Eastern Cordillera (EC) were studied using a digital elevation model (DEM). From the DEM, longitudinal profiles were created and normalized channel steepness (K_sn) values calculated from plots of drainage area vs. slope. Knickpoints in the longitudinal profiles can record transient perturbations or differential uplift. Calculated K_sn values indicate that the EC is experiencing high rates of uplift, with the highest mean K_sn values occurring in the Cocuy region. Mean channel steepness values along strike of the foothills are related to increasing uplift rates from south to north. In contrast, we suggest that high channel steepness values in the south appear to be controlled by high rates of annual precipitation.