Morpho-Tectonics of Transpressional Systems: Insights From Analog Modeling

Transpressional margins are widespread, and their dynamics are relevant for plate boundary evolution globally. Though transpressional orogen evolution involves a topographic response to deformation, many studies focus only on the structural development of the system ignoring surface processes. Here, we present a new set of analog models constructed to investigate how tectonic and surface processes interact at transpressive plate boundaries and shape topography. Experiments are conducted by deforming a previously benchmarked crustal analog material in a meter-scale plexiglass box while controlling erosion through misting nozzles mounted along the transpressional wedge. To analyze the experiments, we generate digital elevation models from laser scans and conduct image correlation analysis on photos taken during experiments. We focus on three experiments that cover a range of erosional conditions and shortening stages (two end-member erosion models and a dry reference). In all experiments, a bivergent wedge forms, and strain partitioning broadly evolves according to previously established models. Regarding drainage networks, we find that the streams in our models develop differently through feedback between fault development and drainage rearrangement processes. Differences between end-member erosional models can be explained by the varying response of streams to structure modulated by rainfall. Additionally, erosion may influence the structural evolution of transpressional topography, leading to accelerated strike-slip partitioning. From these results, we create a model for developing structures, streams, and topography where incision and valley formation along main structures localize exhumation. We apply insights from the models to natural transpressional systems, including the Transverse Ranges, CA, and the Venezuelan Andes.