Growth and lateral propagation of fault‐related folds in the Siwaliks of western Nepal: Rates, mechanisms, and geomorphic signature

Abstract

[1] We study the controls on drainage development in tectonically active regions using a numerical tectonic surface processes model combining tectonic uplift caused by faultrelated folding with erosion by fluvial incision, hillslope diffusion, and landsliding. Our model shows the fundamental control exerted by the dip of the detachment underlying the folds on drainage evolution. When the detachment is horizontal, the relative rates of tectonic uplift and fluvial incision control the evolution. For a nonzero dip, in contrast, the lateral displacement gradient associated with fold propagation sets up a lateral slope behind the active structure, which deflects the stream network. We also demonstrate the importance of landsliding for the attainment of realistic and steady state topography. In contrast, discontinuous tectonic movements do not appear to influence the system. We apply our model to the Dundwa fault-related fold ridge (Siwalik, Nepal). We estimate a remarkably low mean propagation rate for different segments of the structure. This finding, together with the structure and morphology of the ridge, leads us to propose that the ridge developed by linkage of several component segments. The drainage evolution predicted when modeling this scenario compares favorably with field observations. Our models provide insights into the dynamics of fault-related fold propagation: In particular, as a result of fault segment linkage, estimates of propagation rate of these structures may be strongly scale-dependent, and the observed morphology and drainage patterns on faultrelated fold ridges may be controlled by fault geometry rather than by the relative rates of tectonics and surface processes.

Recent fold growth and drainage development: The Janauri and Chandigarh anticlines in the Siwalik foothills, northwest India

“…The analysis of the relationships between active tectonics and surface processes/landforms reveals variations in the style of deformation and in the rate and direction of propagation of ridges. Nucleation, growth and lateral propagation of thrust faults interact with erosion to create the long-term drainage patterns (Elliott, 1976;Gupta, 1997;Champel et al, 2002). Drainage pattern has the potential to record evidence of the kinematics of folds and faults (Jackson et al, 1998).…”

Sediment Cascades in Active Landscapes

“…Kuhlemann et al, 2002) or recycled and uplifted along range-bounding reverse faults to form young anticlines (e.g. Champel et al, 2002).…”

Three-Dimensional Growth of Flexural Slip Fault-Bend and Fault-Propagation Folds and Their Geomorphic Expression

“…At the scale of the fault-related folds that we are considering here (approx 5 km × 20 km) we consider that isostasy and mass redistribution are second order effects whose influence is much more regional than a single fault-related fold and can be expressed via regional subsidence/baselevel changes (cf. [20,86]). …”

“…We are aware that several other approaches to modelling fault-related folding have been proposed and documented-such as elastic-dislocation models [79], elastic-plastic finite element models [80,81], and kinematic models such as trishear [82,83], the fault-propagation fold model of Chester and Chester [84] or detachment folding [85]. However, we choose these kink-band models to drive the tectonic component of our coupled model as: (1) they are widely used to construct both regional and local balanced sections in regions of active compressive deformation [86], (2) they are commonly used as the tectonic model when calibrating slip and/or erosion rates from geomorphic indicators on active folds [33,34,36], (3) they have been widely and successfully used to simulate the evolution of structures growing by kink-band migration in the upper crust [14,20,86], (4) they have well-specified velocity (deformation) fields allowing the advective component of deformation to be easily isolated and its effects clearly understood [37,86] as compared to unspecified velocity distributions in elastic dislocation models. At the scale of the fault-related folds that we are considering here (approx 5 km × 20 km) we consider that isostasy and mass redistribution are second order effects whose influence is much more regional than a single fault-related fold and can be expressed via regional subsidence/baselevel changes (cf.…”

“…The manner in which thrust faults propagate and link is now being recognised as crucial to the structural and geomorphic development of fault-related folds [20,21]. It has been argued that such folds grow as a result of thrust faulting events with similar displacements along strike that are terminated abruptly at tear faults, displacement building up over many earthquake cycles until the fault propagates laterally to form a new tear fault [9].…”