Landscape evolution in the Guanacos fold and thrust belt (37° S): Insights from geomorphological and morphometric analysis

摘要

The Guanacos fold and thrust belt, in the northern Neuquen Andes (37 degrees-38 degrees S; 70 degrees 30'-71 degrees 10'W), has been studied by many researchers focusing on the Quaternary tectonic activity, from a morphological to a structural perspective. Additionally, this portion of the Andes is quite peculiar due to the numerous geomorphic processes coeval with neotectonic, such as volcanic, mass-wasting, glacial, and fluvial processes. However, it is not yet clear the impact of each one of these processes on landscape evolution. This paper reviews the evidence for the geomorphological modeling of the Guanacos belt and analyses the effects of the various actuating processes over the drainage network, implementing different and novel morphometric indices. We studied the hypsometry of the main basins in the area and identified knickpoints of the trunk of each basin from the stream profile slope-area plot. Besides, we applied morphometric indices such as the k(sn) and the chi for all catchments to evaluate the state of equilibrium of the stream network and basin divides. Our results show disequilibrium conditions over the entire fluvial network consistent with rockslide deposits and active structures. This study also discusses the usefulness of the applied morphometric indices in an area with low neotectonic slip-rates, great mass-wasting deposits, and glacial erosion. Findings in this matter showed substantial differences in the indices' response whether the analyzed basin was primarily glacial or fluvial carved. Taken together, results in the Guanacos fold and thrust belt suggest that the glacial erosion and the subsequent rockslide deposits are the prime agents for landscape modeling, making it unable to acknowledge the effect of Quaternary tectonic activity. Only when they are absent is it possible to recognize the neotectonic signature over the drainage.