Latitudinal Variation of Denudation in the Evolution of the Bolivian Andes

Abstract

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. introduction The interactions between uplift, climate, and erosion shape mountain belts. The most fundamental relationship is that tectonic uplift builds mountain topography while climate-driven erosion wears it down. Mountain ranges can be idealized to that of a doorstop wedge (Coulomb wedge) which theoretically describes how erosion can influence the distribution of uplift and deformation within the wedge (Dahlen and

From source to sink: Preserving the cosmogenic 10Be-derived denudation rate signal of the Bolivian Andes in sediment of the Beni and Mamoré foreland basins

“…From this, an orographically-controlled latitudinal variation as suggested by Barnes and Pelletier (2006) from various erosion meters for this region of the Andes could tentatively be inferred. For example, an orographicallycontrolled pattern of rainfall that is also reflected in the pattern of denudation has been observed for the western sides of Andes in northern Chile (Kober et al, 2007).…”

Climatic forcing of asymmetric orogenic evolution in the Eastern Cordillera of Colombia

“…Probably one of the most important conclusions has been that active shortening and tectonic uplift may be localized in areas where protracted erosion impacts tectonically active landscapes. Here, focused high precipitation and exhumation result from orographic barriers that intercept moisture and generate powerful erosional regimes on the windward fl anks of an orogen (Horton, 1999;Montgomery et al, 2001;Reiners et al, 2003;Thiede et al, 2005;Barnes and Pelletier, 2006). Beaumont et al (1992) and Willett (1999) argued that the degree of asymmetry of an orogen may be highly dependent on climatic (e.g., precipitation) gradients.…”

Erosion in the Chilean Andes between 27°S and 39°S: tectonic, climatic and geomorphic control

“…This is another situation where the current erosion rate of a dry catchment may be greater than a wet catchment (e.g. Barnes & Pelletier 2006). Recent studies document that catchment mean erosion rates increase non-linearly with slope, so that high transient slopes in dry catchments can lead to high erosion rates (e.g.…”