Experimental deformation and folding in phyllite and paleostress analysis from triangular plot
Speaker: Yu-sheng Liang
Abstract
A phyllite has been experimentally deformed in various orientations at room temperature and high confining pressure (mainly 5 kb). It glides easily on the foliation in favorable orientations. However, when the foliation is oriented nearly parallel to the direction of compression, folds of similar form are extensively developed, especially when the specimen is constrained in a thick metal jacket. The folds have axial planes of several orientations and include kinks, conjugate folds, and more tightly appressed similar folds. The latter have axial planes approximately perpendicular to the original orientation of the foliation and are shown to evolve from the interaction of oppositely inclined kink bands. Up to about 50 per cent shortening, the deformation proceeds by growth of the kinked regions, within which little further strain occurs, rather than by progressive deformation simultaneously in all regions. All the structures developed bear close resemblance to natural structures, suggesting geometrically similar evolution in spite of different conditions of pressure, temperature, and time. A kink-band can be graphically represented as a point on an equilateral triangle whose vertices define the ,angles between external foliation and kink plane. between internal foliation and kink plane. and between Internal- and external-foliations. The three linear relationships between each of the kink-band angles and the inclination of the £m1 -axis with respect to the unrotated layering can be transformed into II straight line on the triangular plot. Application of this plot in paleostress analysts is demonstrated by several examples.
Reference
Paterson, M.S. and Weiss, L.E. (1966) Experimental deformation and folding in phyllite. Geological Society of America Bulletin 77, 343-374.
Srivastava, D.C. ,Lisle, R.J. ,Imran, M. and Kandpal, R. (1998) The kink-band triangle: a triangular plot for paleostress analysis from kink-bands. Journal of Structural Geology 20,1579-1586.