Kinematic modelling of extensional fault-propagation folding

Many studies have shown that in extensional basins discrete faulting at depth is commonly linked to more distributed deformation, in particular folding, at higher levels. Such extensional fault-propagation folds are particularly common where there is a distinct mechanical contrast between faulted basement and sedimentary cover. Outcrop and analogue modelling studies indicate that such folds form as upward widening zones of distributed deformation (monoclines) above discrete faults at depth. With increasing displacement (strain) the folds are cut by faults as they propagate upwards into the cover. To date, however, there has been little investigation into the kinematics of linked basement faulting and extensional fault-propagation folding. Here we present a two-dimensional kinematic model of linked basement faulting and fault-propagation folding which is based upon trishear. The model allows investigation of the influence of shear zone geometry and the rate of fault propagation upon the style of folds and the strains associated with them. The evolution of linked basement faulting and folding predicted by the model is compared in detail to that observed in an analogue model. The kinematic model reproduces well many of the features seen both in the analogue model and reported from outcrop and seismic studies.