KINK DEFORMATION AND MINERALIZING PROCESSES

Kink or crenulation deformation is a poorly understood structural process that affects rocks in many structural regimes. Three characteristics unite this style of deformation across a disparate range of geological settings and ages. These are: 1) kink deformation most commonly occurs late or last in the deformation history of the host rocks; 2) kink folds and associated crenulation cleavage commonly occur at unexpected stress orientations with respect to inferred stress fields that have produced previous folds and faults in the host rocks; and 3) kink deformation can occur during the waning stages of mineralizing hydrothermal activity, and thereby may contribute to mineralizing processes. Importantly, the contribution of kink deformation-related mineralization to otherwise mineralized rock may offer an economic contribution that is overlooked in comparison to visually more significant veins and disseminations.

The formation of kink folds and associated crenulation cleavage appears to form at depths ranging from near surface to the brittle-ductile transition zone. Regardless of depth, kink folds are best developed where σ1 is parallel to rock layers. Sigma 2 and 3 are inferred to be nearly equal to one another and slightly less than σ1 thus producing a near isotropic stress regime. Conversely, where σ sigma 1 is perpendicular to rock layers, it is unlikely that kink folds will be developed. Kink folds occur at a range of scales and intensities. Where kink folds are open or large, they can be confused with folds of other deformation episodes.

Hydrothermal fluid flow and mineralization can occur along fractures orthogonal to kink axial planes and in kink axial plane fractures. Fluid flow along axial planar crenulation cleavage surfaces is rare, but deformation of pre-existing alteration and ore minerals is common. Fluid pumping may occur during relaxation of the confining stresses that produce kink deformation. Assessment of the role kink fold structures may play with mineralizing processes can be important to the economic evaluation of an ore deposit.