Tectonic and Climatic Controls on the Spatial Distribution of Denudation Rates in Northern Chile (18 degrees S to 23 degrees S) Determined From Cosmogenic Nuclides

摘要

In the arid region of northern Chile the environmental conditions are favorable for measuring tectonic and climatic influences on catchment denudation rates in the absence of vegetation. Previous studies of denudation rates from cosmogenic Be-10 and Al-26 concentrations are limited to single drainages. In this study, we examine catchment-to orogen-scale spatial variation in denudation rates between 18 and 23 degrees S in the Coastal and Western Cordilleras of northern Chile. Be-10 and Al-26 data were obtained from 33 catchments to examine the relative roles of tectonics and climate on catchment-averaged denudation rates. At broader scales, we examine whether denudation rates and orogen topography reflect the 3-D plate geometry of the region. Cosmogenic nuclide-derived denudation rates range from 0.4 +/- 0.5 to 20.6 +/- 1.5 m/Myr in the Coastal Cordillera and from 1.4 +/- 0.7 to 168.0 +/- 19.8 m/Myr in the Western Cordillera. The controls on the denudation rates are evaluated using a statistical factor analysis of 10 selected catchment parameters. Denudation rates indicate a strong linear relationship with channel steepness indices but insignificant correlations and covariation with mean annual precipitation rates, drainage area, stream order, mean elevation, mean local relief, mean basin slope, and grain size of the sampled sediments. Moreover, denudation rates are better correlated with tectonic controls at catchment scale than orogen-scale plate tectonics in the Western and Coastal Cordillera.