Quantifying the spatial and temporal trends of surface uplift in the Andes is critical to understand the drainage evolution of adjacent basins, and in particular to decipher the interplay between major landscape modifications and major biodiversity trends. The La Tatacoa area in the Andes of southern Colombia was a humid tropical region in the middle and upper Miocene but is at present a dry tropical forest area located west of a 3 km-high basement, the Garzon Massif, in the Eastern Cordillera. This major climatic shift in La Tatacoa is thought to be caused by the rainshadow effect triggered by surface uplift of the Garzon Massif. In this project, we aim at constraining the age of aridification and thus indirectly to date the topographic growth of the Eastern Cordillera through the study of erosion rates at three main times: (a) in middle/upper Miocene times, by estimating cosmogenic radionuclide-derived paleo-erosion rates in the well-dated, westerly sourced Gigante Formation; (b) in Quaternary time, by means of mapping and luminescence dating of alluvial terraces; and (c) at present times, by studying catchment-wide 10Be-derived erosion rates through modern river sediments. In addition, we will provide an updated account of exhumation patterns in the Garzon Massif by compiling all available thermochronometric information, acquiring new (U-Th)/He ages in apatites in zircons in selected areas, and, finally, extracting tectonic and uplift rates using 3D thermokinematic modeling of all thermochronometric data. The results of this research will reveal when the eastern Andes limiting the northwestern Amazon basin reached a critical elevation that activated increased precipitation and hence enhanced erosion and sediment transfer to the eastern basins. Such information will be fundamental to feed numerical models that assess the competing role of dynamic topography, surface processes and flexure in configuring the transcontinental Amazon basin.
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