Ptygmatic folds

Ptygmatic folds (from πτύσσω, to buckle in ancient Greek) involve an irregularly folded, isolated “layer”, typically a quartzo-feldspathic vein in a much more ductile schistose or gneissic matrix. They occur in high-grade rocks, mostly migmatites as trains of rounded and near-parallel, commonly concentric folds in which the amplitude is large (>10) and the wavelength small with respect to the almost constant layer/vein thickness (meander-like pattern). They have a lobate, tortuous to squiggled appearance (for example, limbs fold back on themselves and the interlimb angle is negative) and tend to be polyclinal; however, they have no axial plane foliation

J.-P. Burg.

You can also see in the photo below that the folds have multiple wavelengths: a short wavelength (couple cm) on top of a larger (couple meters). There is a second, thinner vein with shorter small wavelength and larger long wavelength (bottom left corner).

The image is a mosaic of several high resolution images. I must figure out how to publish an HD image. Location: Broken Hill, NSW


About the author

The material or views expressed on this Blog are those of the author and do not represent those of the University.  Please report any offensive or improper use of this Blog to
Skip to toolbar