The dynamics of fold-thrust tectonic wedge: An insight from impeccable simulation of Physical Sandbox Experiment with Finite Element Model.

Abstract

The deformation associated with the evolution of fold-thrust tectonic (FTT) wedge has been in the focus of research due to their association with hydrocarbons resources. Analogue sandbox modelling has been proven to be useful in characterizing FTT wedge. However, it is less convenient to interpret the influence of complex boundary conditions and material rheological parameters and to derive the stress distribution pattern from the analogue models. Nonetheless, these challenges can be accomplished competently by means of an exact numerical equivalence of those analogue models. Therefore, we undertook a numerical replication of the analogue sand-box with an absolute identical set up. This makes the attempt unique from earlier approaches, where lengths, rheology, and/or cohesive strengths were likely varied for converging the solutions in codes. Here, propagation parallel profile of sandbox experiments is numerically modelled in a 2-dimensional (2D) space with a plain strain assumption. For simplicity, the models are devoid of complex geological phenomena such as isostasy, pore fluid pressure and surficial processes. The present model enforces an elastoplastic constitutive relationship having exactly same rheology as our sand-box model. The model comprises cover material resting over a rigid decollement with frictional interaction. The cover material is subjected to asymmetrical push from one end as in physical experiment. With the identical rheology, dimensions, and geometry our numerical model successfully produced comparable results with our physical sandbox models. The measured kinematic attributes of the wedge such as taper angle, wedge width, thrust spacing, displacement along thrust from our numerical model are found in good agreement both qualitatively and quantitively with their analogue counterparts. The dynamics of deformation has also been investigated by extracting the magnitudes of stresses from each node of the numerical mesh of the present models.  From the dynamic analysis, the spatial distribution of stresses revealed that within a deforming wedge all the stress parameters are maxed periodically at a certain distance away from the pushing end boundary. The position of maximum stress is found consistent with the zone localized failure. Monitoring the periodic peaks of stress approximate the location of failure, in return leading to measure the thrust spacing. Furthermore, empirical relationships for stress distribution within a collisional wedge have been successfully developed from the observed stress distribution patterns. With the help of these relationships, mathematical expressions were developed for predicting 2D curvature of a thrust plane within a tectonic wedge.