Abstract
The three-dimensional growth of fault-related folds is known to be an important process during the development of compressive mountain belts. However, comparatively little is known concerning the manner in which fold growth is expressed in topographic relief and local drainage networks. Here we report results from a coupled kinematic and surface process model of fault-related folding. We consider flexural slip fault-bend and fault-propagation folds that grow in both the transport and strike directions, linked to a surface process model that includes bedrock channel development and hillslope diffusion. We investigate various modes of fold growth under identical surface process conditions and critically analyse their geomorphic expression. Fold growth results in the development of steep forelimbs and gentler, wider backlimbs resulting in asymmetric drainage basin development (smaller basins on forelimbs, larger basins on backlimbs). However, topographies developed above fault-propagation folds are more symmetric than those developed above fault-bend folds as a result of their different forelimb kinematics. In addition, the surface expression of fault-bend and fault-propagation folds depends both on the slip distribution along the fault and on the style of fold growth. When along-strike plunge is a result of slip events with gently decreasing slip towards the fault tips (with or without lateral propagation), large plunge-panel drainage networks are developed at the expense of backpanel (transport-opposing) and forepanel (transport-facing) drainage basins. In contrast, if the fold grows as a result of slip events with similar displacements along strike, plunge-panel drainage networks are poorly developed (or are transient features of early fold growth) and restricted to lateral fold terminations, particularly when the number of propagation events is small. The absence of large-scale plunge-panel drainage networks in natural examples suggests that the latter mode of fold growth may be more common. The advective component of deformation (implicit in kink-band migration models of fault-bend and fault-propagation folding) exerts a strong control on drainage basin development. In particular, as drainage lengthens with fold growth, more linear, parallel drainage networks are developed as compared to the dendritic patterns developed above simple uplifting structures. Over the 1 Ma of their development the folds modelled here only attain partial topographic equilibrium, as new material is continually being advected through active axial surfaces on both fold limbs and faults are propagating in both the transport and strike directions. We also find that the position of drainage divides at the Earth’s surface has a complex relationship to the underlying fold axial surface locations.
Highlights
Fault-related folds, and the blind faults they are associated with, are being increasingly recognised as extremely important both from a scientific and a socio-economic viewpoint [1,2,3,4,5,6]
This paper has investigated, through numerical modelling, the geomorphic and structural expression of some key aspects of the three-dimensional growth of flexural-slip fault-bend and fault-propagation folds
We find that the surface expression of fault-bend and fault-propagation folds depends on both the slip distribution along the fault and on the style of fold growth
Summary
Fault-related folds, and the blind faults they are associated with, are being increasingly recognised as extremely important both from a scientific and a socio-economic viewpoint [1,2,3,4,5,6]. The kinematic development (in the transport direction) of individual structures is much debated, with growth strata associated with ancient examples being cited as evidence for kink-band migration (flexural slip) and/or limb rotation [4,12,13,14,15,16]. We report here results from a coupled kinematic and surface process model of fault-related folding in an effort to better define the geomorphic expression of two different conceptual models of flexural-slip fault-related fold growth. We consider flexural-slip fault-bend and fault-propagation folds that grow in both the transport and strike directions. Our modelling is driven by the desire to answer the following questions derived from observations of natural structures: (a) Given the along-strike displacement and topographic gradient seen in many natural folds (Figure 1), why are plunge-panel (transport-perpendicular) drainage networks rarely seen in natural fault-related folds?
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.