Regional landscape response to thrust belt dynamics : the Iglesia basin, Argentina.

Abstract

Intermontane basins are often the result of regionally variable uplift in tectonic settings. Wedge-top basins, a type of intermontane basin, form along thrust faults within a fold and thrust belt, and provide an ideal environment to study the regional fluvial and surface response to local variations in rock uplift. This study simulates the formation and evolution of an intermontane basin using a landscape evolution model. The modelling results demonstrate that large trunk streams maintain connectivity during basin formation for two reasons: (1) their stream power is enhanced by the capture of smaller streams, enabling them to incise through the uplifting downstream region, and (2) they acquire increased sediment yield to completely infill the upstream accommodation space rather than forming an endorhic basin. During active deformation of the fold-and-thrust belt, both channel slope and erosion rates are reduced upstream of the intermontane basin and these changes propagate as a wave of low erosion into the uplands. For a uniform background uplift rate in a landscape previously at steady state, this reduced rate of erosion results in a net surface uplift upstream of the basin. Following the eventual breach of the basin’s bounding structural barrier, a wave of high erosion propagates through the basin and increases the channel slope. This onset of increased erosion can be delayed by up to several million years relative to the onset of downstream uplift. Observed paleoerosion rates in paired wedge-top and foreland basin sequences, and presentday stream profiles in the Argentine Precordillera support our modelling results. Our results may be extrapolated to other foreland systems, and are potentially identifed using low-temperature thermochronometers in addition to paleoerosion rates.