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Latitudinal Variation of Denudation in the Evolution of the Bolivian Andes

Jason B. Barnes and Jon D. Pelletier

Department of Geosciences, University of Arizona, 1040 E. Fourth St., Tucson, Arizona 85721

Present address of corresponding author: Department of Geological Sciences, University of Michigan, 2534 C.C. Little Building, 1100 N. University Avenue, Ann Arbor, Michigan 48109-1005; barnesja{at}umich.edu

Latitudinal gradients in topography, relief, climate, and deformation have been used to suggest that climate-driven erosion has exerted a first order control on the development of the central Andes. We synthesize the spatial and temporal variations in denudation across the eastern Bolivian Andes (14-22°S) from new and existing estimates to test whether physical evidence exists to support the hypothesis that erosion influences thrust belt evolution. Basin-morphometry, channel network indices, climate, and longitudinal river profiles indicate a northward increase in relative relief, fluvial incision, and denudation. Short-term denudation-rate averages from landslide mapping and sediment-flux data range from 1 to 9 mm/yr in the north compared to 0.3 to 0.4 mm/yr in the south. Long-term denudation-rate estimates from thermochronology, cosmogenic radionuclides, foreland basin sediment volumes, stratigraphy, paleoerosion surface degradation, and balanced cross sections range from 0.04 to 1.6 mm/yr with rates up to more than twice as fast in the north when comparing estimates from the same method. The shorter-term denudation rates exhibit the greatest variance. Our denudation synthesis shows that an along-strike disparity in denudation (greater in the north) has existed throughout the Holocene and perhaps existed since as early as the late Miocene. Our denudation synthesis also suggests that the disparity and denudation rates have increased to the present. Correlations between the thrust belt geology, geometry, geomorphology, climate, and kinematics of the orogenic wedge provides a case study in observing the regional scale interactions between uplift, climate, and erosion. We conclude that the denudation history, uplift history, and tectonic-geomorphic correlations suggest that models of the evolution of the Bolivian Andes should incorporate a latitudinal erosion gradient for the last 10 kyrs to perhaps 10 Myrs.

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