Limits of Fluvial Relief in the Northern Andes

Abstract

The eastern flank of the tropical Northern Andes (0.5–3.5°N) is characterized by variations in tectonic style due to strain partitioning, and thus an ideal setting to explore how along-strike differences in rock uplift rate scale with relief and elevation. Here we quantify erosion and topography and their relationship along the Eastern Cordillera using new cosmogenic nuclide data, previously published thermochronology data, and topographic metrics. We found higher median cosmogenic nuclide-derived erosion rates along the southern and northern sections of the study area (∼600 m/Myr) compared to the central part (∼140 m/Myr). The same trend is observed in erosion rates derived from thermochronology data, with values of 360 m/Myr in the south and north, and 160 m/Myr in the central zone, indicating that erosion patterns have remained constant since at least Pliocene times. Spatial variations in erosion rate correspond to changes in structural style due to strain partitioning; high erosion rates in the north and south are associated with dominant reverse faulting, while lower erosion rates in the central region coincide with dominant strike-slip deformation. Cosmogenic nuclide erosion rates and channel steepness follow a power law relationship with a slope exponent n = 2.2—corresponding to a high sensitivity of erosion to channel steepness. This nonlinear-scaling between erosion and topography derived from local erosion data is consistent with along-orogen differences in channel steepness index, fluvial relief, and maximum elevation. Erosion rates in the northern and southern zones are ∼4.3 times higher than those in the central zone, but topographic metrics such as channel steepness, maximum elevation and fluvial relief are only ∼1.2–1.8x greater. This suggests that high sensitivity of erosion to channel steepness, likely caused by incision thresholds combined with steady river discharge, limits along-orogen differences in relief along the Northern Andes.