The application of drainage system analysis in constraining spatial patterns of uplift in the Coastal Cordillera of northern Chile
Anne E. Mather, Adrian J. Hartley, 2006. "The application of drainage system analysis in constraining spatial patterns of uplift in the Coastal Cordillera of northern Chile", Tectonics, Climate, and Landscape Evolution, Sean D. Willett, Niels Hovius, Mark T. Brandon, Donald M. Fisher
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The Coastal Cordillera of northern Chile is the only subaerial part of the South American continental crust in direct contact with the subducted Nazca plate. Deformation of the cordillera can be directly related to plate coupling at the subduction zone. Knowledge of uplift rate variation along the coast is however limited, mainly due to difficulties in dating and correlating the discontinuous remnants of marine terraces. This paper uses geomorphology and the stream gradient index (SGI) to examine 80 drainages along 200 km of coastline between 21°S and 23°S. Selected catchments are located on similar geology (basaltic andesite and granodiorite) and within the same coastal climate zone. The southernmost part of the transect overlaps with an area of known uplift rates based on dated marine terraces. Characteristics of the SGI index, combined with the geomorphology, enable the coast to be divided into two sectors. Extrapolation of the SGI values from an area of known (sector 1) to unknown uplift rates (sector 2) enables an estimate of relative uplift rates for sector 2. Sector 1 has known uplift rates of 240–384 mm k.y.−1. The SGI results suggest sector 2 has overall uplift rates which may be 2–3 times greater than sector 1. The large-scale (70–100 km) differences in apparent differential uplift reflected by the SGI along the Coastal Cordillera are tentatively attributed to aseismic ridge subduction. Smaller-scale (30 km) variations in the SGI associated with the major regional drainages in sector 2 suggest that the latter drainages may be focused in structural lows (with low SGI values) controlled by NE-SW– to E-W–trending reverse faults, although further work is required to clarify this.