River network response to thrust sheet propagation into a foreland

Orogenic growth, characterized by formation and forward propagation of foreland fold-thrust belts, is a process predicted by wedge models of thrust sheet systems. During this process, the drainage network is disrupted by differential uplift and shortening across thrust ramps and lateral structures linking thrusts. Transverse rivers are often diverted into longitudinal reaches parallel to thrust faults, where they converge into larger river systems, thereby altering the river network patterns. Whether these patterns contain fingerprints of past tectonic events can be elucidated through numerical modeling of coupled tectonics and river network evolution.

To investigate the effects of isolated thrust sheet propagation on drainage networks, we use a numerical two-dimensional landscape evolution model, the Divide and Capture model (DAC), which integrates numerical solution of fluvial incision and analytical hillslope processes for both diffusive and slope-limited processes on an adaptive grid. As a Lagrangian reference-frame model, river channel courses are accurately tracked, even with topographic advection. We model a growing bivergent, orogenic wedge as a shortening region with  multiple isolated thrust sheets, consisting of a shortening structure with flat-ramp-flat geometry.  Faults have finite strike length and strike-slip linking structures, constructed to build a strain-compatible model with equal convergence along strike.  Convergence velocity is oriented perpendicular to the thrust sheets and is absorbed by each fault through a specified slip rate.

The modeling results reveal a non-steady and dynamic landscape, characterized by locally high uplift rates and significant relief above ramp structures. The river network responds dynamically to the propagation and displacement of thrust sheets. Interestingly, the largest transients and river capture events are not associated with the uplift zones, but rather with the strike-slip linking structures. Rivers draining the uplift blocks are relatively stable, but longitudinal rivers parallel to thrusts are often blocked, forming unstable closed basins or are forced to cross transfer structures,  undergo significant offset and eventual river capture events. We conclude that horizontal advection, and its variation across a complex 3-D fold-and-thrust system, rather than localized uplift, dominates the reshaping of a river network above the propagated thrust foreland.