Effects of tectonic deformation and landslides in the erosion of a mountain plateau in the transitional zone between the central and Patagonian Andes

Abstract

Valley downcutting and tectonically-related landslides have driven the evolution of the landscape in the transitional zone between the Central and Patagonian Andes. Since the onset of the basin9s development, around 300 km3 of rock have been eroded from the plateau. Three-quarters of the erosion occurred in the area undergoing tectonic uplift. Bedrock landslides estimated between ∼31 to 5 ka caused significant hillslope erosion, at a rate of 0.318 km3/ka, and created seven dams. Despite their capacity to remove large amounts of rock from hillslopes, by creating dams, landslides have graded fluvial courses to local base levels and sediments have been trapped at timescales lasting tens of thousands of years. Around 95 percent of the total rock volume involved in large rockslides still remains in the depositional area. Only post-glacial retreat landslides are observed in the mountain area (which was glaciated during the Last Glacial Maximum, LGM), and the only landslide event contemporary to the LGM is located in the piedmont area. These facts indicate that in arid regions such as the study area, landslides do not constitute an important source of sediments to the foreland if there is a lack of coupling between them and an effective massive erosion agent, such as a glacier. Although the removal of large amounts of rock from valley slopes contributes to the degradation of the relief generated by uplift, the results presented here suggest that they might also have counteracted the effects of tectonic uplift by interrupting the sediment flux cycle, trapping sediments and creating positive sediment balances.