Abstract

Landscapes in tectonically active regions develop in response to a complex interplay between rapid tectonic deformation and surface processes. In order to understand the evolution of these environments and distinguish between the different factors, it is fundamental to identify and quantify geomorphic processes and rates on different time scales. The forearc of south-central Chile provides an ideal setting to elucidate the response of surface processes to climatic and tectonic forcing. However, in contrast to northern Chile, this region has attracted little attention due to difficulties in quantifying the age of geomorphic surfaces.

We use luminescence and stable cosmogenic nuclides (3He, 21Ne) on conglomeratic units in the Central Depression and fluvial valley fills in the Coastal Cordillera to constrain exposure and burial ages of these units that form major landscape elements in the southern Chilean forearc. Our data indicate that disturbances in the drainage network are controlled by local uplift, which may be caused by deformation above an active blind thrust. In the Coastal Cordillera, local short-term uplift rates reach a minimum of 0.27 mm a−1 and are on the same order as late Quaternary minimum incision rates of 0.15 mm a−1 to 0.43 mm a−1. The valley fills in the Coastal Cordillera have depositional ages of 80 ka and 255 ka, respectively. Exposure ages of the extensive alluvial surfaces in the Central Depression cluster between 135 ka and 175 ka and between 240 ka and 280 ka. Hence, the deposition of these surfaces broadly coincides with marine isotope stages (MIS) 6 and 8 and appears to be climatically driven.

You do not currently have access to this article.