THE ROLE OF FLEXURAL SLIP IN THE DEVELOPMENT OF MULTILAYER CHEVRON FOLDS

Chevron folds are characterized by straight limbs and narrow hinge zones. One of the conceptual models to initiate and develop chevron folds involves flexural slip during folding. While some kinematical models show the necessity for slip to initiate during chevron folding, recent numerical modeling studies of visco-elastic effective single layer buckle folding have shown that flexural slip does not result in chevron folds. In this study, several 2D finite element analysis models are run, distinguished by 1) geometry of the initial perturbation (sinusoidal and white noise), 2) varying the wavelength of the initial perturbation (10%, 50%, and 100% of the dominant wavelength) and 3) variation of the friction coefficient (high and low friction coefficient between interlayers). All numerical simulations apply 60% of shortening, in order to achieve inter-limb angles of 60 to 70 degrees.

The results show that for sinusoidal initial perturbations, systematic and symmetric chevron folds are reproduced when 10% of the dominant wavelength is used for the initial perturbation. Using 50% or 100% of the dominant wavelength results in circular and sinusoidal folds, respectively. Low friction coefficient models result in larger amplitudes and sharper inter-limb angles compared to high friction coefficient models. For white noise initial perturbations, isolated and asymmetric chevron folds are developed when the friction coefficient is low. High friction coefficient models reproduce the dominant wavelength without chevron folds and low friction coefficient models result in a different dominant wavelength. In all chevron folds models, slip initiates at the early stages of folding (i.e. 1% to 5% of shortening). This is in contrast with field observation in the Meguma Group, Nova Scotia, Canada where slip is observed to occur during the later folding stages when inter-limb angles reach 60-70 degrees. It is of note that comparing with effective anisotropy models, all effective single layer chevron fold models do not reproduce hinge collapse.