Restoration and balance of complex folded and faulted rock volumes: Flexural flattening, jigsaw fitting and decompaction in three dimensions

Techniques of two-dimensional bed length and cross-sectional area restoration are extended into true, three-dimensional (3-D) restorations using the preservation of areas of individual surfaces plus conservation of volume between surfaces. The flexural flattening technique involves the restoration of a complexly folded surface to a horizontal plane while conserving surface area and minimising finite strain. Multiple surfaces showing superimposed non-co-axial folding may be restored using the flexural flattening method applied to successively deeper surfaces. In the process of sequential restoration, volumes between the uppermost flattened surface and underlying surfaces are preserved and therefore the method is volume-balanced. The jigsaw fit of footwall and hangingwall cut-offs of each flattened surface, in map view, provides a unique restoration solution based on a unique translation and/or rotation of the hangingwall block. Flexural flattening and jigsaw fit performed sequentially on successively deeper surfaces in a three-dimensional model may incorporate removal of the uppermost layer and three-dimensional decompaction at each restoration step. The method is applied to a synthetic 3-D growth fault structure which has been produced using multiple discrete slip vectors and bulk simple shear hangingwall deformation.