The structural and morphological evolution of transpressive systems:
insights from analog modeling
Abstract
The relationships between deformation and erosion in transpressive
systems are still poorly understood. Here, we present a new set of
analog models to investigate how the tectonic and surface processes
present at transpressive plate boundaries interact to shape topography.
The experimental setup comprised a 2 x 1 x 0.5 m3
plexiglass box fit with a plexiglass board cut to 20º obliquity. A motor
pulled a mylar sheet beneath the board to generate a velocity
discontinuity at the interface. We loaded a ~5 cm thick
layer of a granular material onto the board and sheet composed of 40 wt.
% silica powder, 40 wt. % glass microbeads, and 20 wt. % PVC powder
(cf. CMII in Reitano et al., 2020, doi: 10.5194/esurf-8-973-2020). This
setup allows deformation to nucleate at the velocity discontinuity and
naturally form a transpressional wedge. The model was monitored with
digital cameras and a laser scanner to conduct particle image
velocimetry and digital elevation model analysis, respectively. To
explore surface processes associated with mass transport and erosion, we
used a sprinkler system that casts a uniform mist across the model
surface. We allowed ~1 cm of relief (equivalent to
~10 cm of convergence) to form before misting began to
ensure the formation of realistic drainage networks. Before misting,
experiments evolved in 3 stages: 1) distributed strain, 2) strike-slip
faulting along synthetic structures, and 3) uplift and formation of a
wedge along bivergent thrust structures. After misting, strike-slip
deformation was still fully partitioned to synthetic structures and
thrust sheets propagated in the prowedge direction. As the experiment
continued, sub-longitudinal drainage systems formed with their
orientation controlled by synthetic structures. Strike-slip displacement
along these structures interrupted transverse streams, which ultimately
captured the sub longitudinal systems. On the retrowedge, a longitudinal
basin formed along a coalesced extensional structure, which also was
later captured by transverse channels. These and other interactions
between fault structures and channel networks provide insight into
erosion and mass transport in transpressional systems and the nature of
the complex reorganization of stream networks in response to
deformation.