The Influence of Localized Glacial Erosion on Exhumation Paths in Accreting Coulomb Wedges: Insights from Particle Velocimetry Analysis of Sandbox Models

Abstract:

Glacial erosion can have an impact on the location and development of faults in mountain belts. The rapid removal and deposition of rock, in some cases, is thought to affect the initiation of slip on older fault structures, or cause the development of new structures within the older part of the wedge. We present cross-sectional data from both erosional and non-erosional sandbox models of Coulomb wedges in order to quantify the impact of localized erosion on the location of and slip on deformational structures, as well as the general path of material through a wedge. To do this, we employ Lagrangian particle tracking velocimetry (PTV) using the open-source Python PTV toolkit trackpy, among a suite of other data analysis tools. We are able to extract robust and reliable sets of particle trajectories from a series of images without the need for predefined markers or marker-beds, instead identifying and tracking natural variations in sand color as individual particles. By comparing the motion of particles in cross-section to the local surface topography over an entire experiment, we determine a high-resolution record of exhumation rates, in addition to simple uplift rates. These comparisons are further informed by the use of high-definition Eulerian particle image velocimetry (PIV), which provides quantitative data about the distribution of deformation and instantaneous material displacements throughout a cross-sectional view of a Coulomb wedge. This allows us to interpret these pathways in relation to the behavior of active structures and general wedge morphology. In our experiments, we observe that localized glacial erosion has an impact on material pathways, in the form of an increased rate of exhumation locally, more vertical trajectories towards surface below the zone of erosion, and reactivation of older structures to maintain force balance within the entire wedge.