Cenozoic Uplift Rate History of South America from Inversion of River Profiles
Friday, 19 December 2014
It is generally accepted that the long wavelength shape of a longitudinal river profile is mainly controlled by uplift rate history and moderated by erosion, both of which can vary as a function of time and space. Thus, knowing the shape of a river and adequately parametrizing the erosional processes, it is feasible to retrieve spatial and temporal patterns of regional uplift rate by applying an inversion scheme. Here, a damped, non-negative, least-squares algorithm is used to model a drainage inventory from South America. The aim is to determine the uplift history of this continent. ~1800 river profiles were extracted from a digital elevation model of South America and their fidelity was checked using satellite imagery. The inverse problem is then solved by minimizing the misfit between observed and predicted river profiles as a function of uplift rate, which is allowed to vary smoothly as a function of time and space. Erosional processes are modelled using an advection-diffusion formulation, which includes both detachment-limited and transport-limited forms of erosion. The parameter space of the erosional model is constrained using independent observations of uplift and incision rate histories from different locations across South America. Residual misfit between observed and calculated rivers is small, demonstrating that coherent signals occur on different river profiles and uplift events across South America can be resolved. Inversion results suggest, for instance, rapid growth of the Andes from an elevation of ~2 km to ~4 km within the last 20 Ma. Youthful uplift occurred in the northern Andes, whereas the central and southern Andes appear to have grown mainly within the last 10 Ma. The Borborema Province also experienced uplift (1–2 km) during the last 20 Ma. Calculated uplift histories are consistent with independent spot measurements of uplift constrained by, for example, thermochronology, stable-isotope altimetry and carbonate-clastic sedimentation offshore.