COUPLING FORWARD MODELING AND STRUCTURAL RESTORATION TO BETTER UNDERSTAND DEFORMATION MECHANISMS OF FAULT-RELATED FOLDS

Understanding structural deformation through time is important in geosciences to characterize processes of faulting, folding, and other rock strain. Forward modeling methods allow us to examine how rocks may deform. However, forward modeling presents drawbacks such as the assumption of an initial paleo-geometry, which is rarely known, and often proves unable to precisely reproduce aspects of natural structures. Structural restoration is another approach that retro-deforms the present-day geometry using simple geometrical, kinematical, or/and geomechanical rules. While restoration approaches benefit from working with known present-day geometries, they generally suffer from simplified mechanics and the challenges to implement boundary conditions that effectively reproduce nature. In an attempt to help overcome these limitations, we develop a series of mechanical forward models that reflect natural fault-related fold geometries and restore them using these methods.

We use the Distinct Element Method (DEM), a numerical approach that represents a domain with small particles and mechanically deforms it, to build several 3D forward models: four in compression and two in extension. All models have pre-growth and growth strata, and present emergent fault-related folds. For the pre-growth, we test the impact of bed thickness and of flexural slip surfaces. We show that pre-growth thickness can influence fault-related folding styles. Flexural slip leads to fault-propagation fold when the pre-growth is thick, and to an asymmetric detachment fold when it is thin. Extensional models with flexural slip accommodate less deformation by secondary faulting. We induce non-cylindrical structures with a frictional contrast at the base of each model, which acts as a detachment.

We restore our DEM models using two, alternative 3D restoration methods. We test a geometrical and a geomechanical restoration methods and show that the DEM provides good benchmarks to evaluate the efficiency and accuracy of these 3D techniques. Both approaches can restore the DEM models if the deformation remains small. However, we observe important discrepancies around faults with larger restored strains. Thus, we explore ways that restoration methods may be improved using appropriate boundary conditions and other constraints.