Patagonian landscape modeling during Miocene to Present-day slab window formation

Abstract

The subduction of seismic oceanic ridges often results in the formation of slab windows, which can affect not only the heat flow and retroarc volcanism, but also the exhumation and topographic evolution of the upper plate. An active and world-class example of a slab window is southern Patagonia, in southernmost South America, which is related to the subduction of the seismic oceanic South Chile Ridge between the middle–late Miocene and the Present day. How the subduction of the ridge and formation of the slab window have influenced the evolution of the Patagonian landscape, exhumation and topography is still under debate. Some works have proposed orogenic deformation mostly affecting the Pacific margin and hinterland areas, or an inherited early Miocene tectonic relief generated before the slab window formation. Others have preferred epeirogenesis hypotheses, such as dynamic uplift or isostatic rebound as a result of lithospheric thinning associated with asthenospheric or lithospheric mantle changes. In this work, we analyze the landscape evolution at medium (orogen-scale) and long wavelengths (embracing the whole of southern Patagonia, from coast to coast) using FastScape a landscape numerical model. This program was coupled with an optimization scheme (the Neighborhood Algorithm) suitable for nonlinear inverse problems. The “goodness” (fit to data) of our landscape evolution models was evaluated using: i) cooling ages, and ii) maximum elevations, in order to provide constraints on the uplift rates, erosion efficiency and effective elastic thickness. We then used the best values to compare two forward models representing medium- versus long-wavelength processes. Our results indicate that long-wavelength uplift geometry (including dynamic uplift and/or lithospheric rebound from thinning) involving areas from the Andes to the Atlantic coast was required from 12 Myr to the Present day in order to reproduce not only the youngest cooling ages but also Present-day topography.