Latitudinal Variations of Denudation Rates along the Western Andes in South America derived from Cosmogenic Radionuclides

Abstract

Tectonic, climatic and biotic forces interact and imprint surface processes that shape topographic relief. The combination of chemical weathering and physical erosion on the Earth’s surface is defined as denudation rate. Catchment- averaged denudation rates are one of the main parameters in geological research to quantify surface processes over millennial time scales. The advantage of this method is to identify the characteristics of surface processes previous to human impact. Denudation rates are derived from cosmogenic nuclides which are rare isotopes that are created by cosmic radiation, such as 10Be and 26Al. Cosmogenic nuclides are produced in the atmosphere (meteoric-produced isotopes) or within the mineral structure of different rock material at the surface (in situ-produced isotopes). In situ-produced 10Be is commonly obtained from quartz which is one of the most frequent minerals on the Earth’s surface and, hence, allows a wide range of applications for this method. The identification of dominant natural controls on surface processes in different environmental settings is challenging. With this study, for the first time, this challenge can be solved by including catchment-averaged denudation rates in multivariate statistical-analyses along with tectonic, climatic and biotic catchment parameters. The objective of this thesis is to investigate the dominant natural controls on catchment-averaged denudation rates within different environmental end-members of the Western Andes in South America. The study area covers the environmental end-members reaching from the hyper arid Atacama Desert to the glaciated regions of the Northern Patagonian Ice Fields. The results of this thesis show that local tectonic processes have the highest influence on denudation rates in the arid to hyper arid environments of northern Chile. In between the environmental end-members the effect of vegetation and precipitation on denudation rate varies depending on the initial vegetation-cover amount. In environments with high initial vegetation cover, vegetation is decelerating sediment transportation and is limiting the maximum variation in denudation rates. In the glaciated environment of the Northern Patagonian Ice Field, the latitudinal variation of denudation rates is dependent on the variations in vegetation cover in glaciated and deglaciated catchments.