Influence of pre-existing salt diapirs on 3D folding patterns

Abstract

The 3D detachment folding instability gives rise to a wide variety of fold shapes (e.g. from dome shape structures to long en-echelon or straight anticlines) as a result of interactions between growing fold segments. The 3D growth of these folds, as well as the wavelength and lateral propagation of folds, is controlled by the physical parameters of a detachment layer and its overburden. However, the existence of initial heterogeneities, such as pre-existing salt plugs within the sedimentary cover, might affect fold development as well.We use numerical modeling to investigate how the fold pattern is affected by pre-existing salt structures. High-resolution 3D folding simulations (with and without pre-existing salt structures) were performed, in which we varied the shape, height and spacing of pre-existing diapirs. In a first geometric setup, we employed a multilayer setup and synthetic diapir distributions in order to study the influence of diapir spacing on fold spacing and patterns. In a second geometric setup, we use a diapir distribution that fits the observed exposed diapir distribution in the southeastern Zagros.Results show that the presence of diapirs does not considerably change the wavelength of the folds, which is in all cases close to the dominant folding wavelength that develops in the absence of diapirs. Yet, the presence of pre-existing structures speeds up the folding instability in those locations and also affects folding patterns as the diapirs localize the initial deformation by accommodating folding above them, which results in the diapirs being located in the core of the folds. If diapir spacing is much smaller than the dominant folding wavelength, diapirs are located in different structural positions such as fold synclines or flanks.