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Transcurrent Tectonics: Structures in the Fault Zones.
On strike-slips faults, stretching lineations have a small pitch angle, i.e. the direction of shearing is sub-parallel to the strike of the fault.
When the sheared domain is layered, or when a mylonitic foliation has developed, strike-slip motion can lead to the formation of drag folds. At an early stage folds develop with vertical axis. As deformation proceeds those axes tend to re-orient themselves to parallel the shear direction (the X axis of the finite strain ellipsoid). When shearing is intense sheath folds may develop (cf picture on the bottom right corner is a section perpendicular to the fold "a" axis). The folding of the mylonitic foliation is very common and should be interpreted in terms of progressive deformation as the finite flattening plane is dragged into the shear zone.
The picture on the right displays sheath folds (Norway) .