Viscoplastic model of mountain building*

Scraping and compression of sediments at convergent tectonic boundaries leads to formation of accretionary wedges. Analogue rheological models for these sediments offer insights into the forces governing the development of these mountain ranges.

We consider a thin-film viscoplastic fluid model of an accretionary wedge, where an initially horizontal fluid layer is scraped off by a vertical backstop that moves at a constant speed. Evolution of the system is controlled by a dimensionless Bingham number Bi. For high Bi, most of the flow is a pseudo-plug, with shear deformation concentrated close to the base. Conversely, for low Bi, the early-time flow is approximately Newtonian, but with a thin pseudo-plug layer at the top. At late times, the low-Bi system approaches a pseudo-plug-dominated regime similar to the one at high Bi.

Numerical solution of the fluid model is used to verify the analytically obtained flow regimes. Additionally, simple model geometry allows us to study the system via analogue laboratory experiments. In all of the conducted experiments, buckling of the fluid surface is observed, resembling fault and fold structures seen in real accretionary wedges.