Impact of synkinematic sedimentation on the geometry and dynamics of compressive growth structures : Analogue modelling insights
Abstract
Analogue sandbox models have been set up to study the impact of synkinematic
deposits on the geometry and evolution of single thrusts and
folds according to different sedimentation modes (a slow or rapid sedimentation
rate that is constant or changing in space and time) and rheological
profiles (thin or thick sedimentary series, with a basal décollement
level or not). A first series of experiments documents the influence
of synkinematic deposits according to their sedimentation rate and the
rheology of the prekinematic materials. A second series investigates the
influence of changes in the sedimentation rate through time. A third one
considers the influence of changes in the sedimentation rate in space.
All these experiments suggest that the geometry and evolution of single
compressive growth structures vary according to the sedimentation rate.
The number and dip of their frontal thrust segments change with the ratio
R between the sedimentation rate (Vsed) at the footwall of the faults
and the uplift rate (Vupl) of their hanging wall. The latter is then more or
less uplifted depending on the dip of the thrusts. As a result, the overall
structure has either a fault-bend fold or a fault-propagation fold geometry.
Those rules are verified when the ratio R (Vsed/Vupl) changes in
space or through time. In addition, the rheological profile of the models
also affects the geometry and evolution of compressive growth structures.
Their structural style, as well as the synsedimentary splitting and
steepening of the associated thrusts, varies according to the occurrence
and strength of the brittle and ductile layers.
According to this modelling study, the ratio R (Vsed/Vupl) and its
changes in space and time, along with the rheology of the deformed
materials, are key parameters to better understand the geometrical and
kinematical complexities of natural growth thrusts and folds and to improve
their interpretation.