Three‐dimensional numerical models with varied material properties and erosion rates: Implications for the mechanics and kinematics of compressive wedges

We develop three‐dimensional mechanical models of a compressive wedge and investigate how the form and kinematics of the outboard wedge are affected by variation in initial topography, material properties, and erosion rate. Inclusion into the wedge of weaker, less dense material affects the form of the wedge, producing a region of steeper average slopes and higher topography while depriving the region further inboard of material. Enhanced erosion has a similar effect. The wedge attempts to replace the eroded material by focusing deformation. The result is a stepped region of lower topography within the outboard of the orogen. We observe that uplift velocities at three points in the orogen vary cyclically from near zero to ∼3 times the average uplift rate over cycles lasting on the order of 15–200,000 model years. Our models, along with analog models and some well‐dated examples from active orogens, suggest that transient accommodation of strain may be common. The cycles observed responded rapidly to changes in the amount of erosion imposed. Our models suggest that orogens may be driven by strong coupling between erosion and strain on temporal scales of 10 4 –10 5 years and spatial scales comparable to the scale of the erosional perturbation. We compare our models to the Puli Embayment of west central Taiwan, a region of anomalous low topography and suggest that it presence may reflect the presence of weaker and more erodible sediments than those present along strike in the orogen.