1997 Volume 8 Issue 3 Pages 143-148
In structurally deformed areas, fold geometry usually varies from point to point ranging from parallel folds to those with thickened hinges. The latter type of folds (i.e. thickened, or T-folds) are believed to form by the superimposition of homogeneous ductile strain during progressive deformation. The geometry of the various folds thus formed appears to be the result of the cumulative effect of, amongst others, both ductile strain and the rheology of the folded material. Understanding of the role of ductile strain and rheology on fold geometry is rather easier for experimentally deformed folds wherein we can “see”all the stages of fold development. In naturally deformed folds, on the other hand, this is not possible and one has to apply mathematical treatment/analysis of the data on fold geometry. Thus, in order to understand how ductile strain and rheology control the shapes of natural folds, a mathematical treatment of a polynomial equation for natural folds has been done in the paper. Since for a polynomial equation, it is very difficult, at times even practically impossible, to understand the functional relations properly, it would be easier to do so if the polynomial is transformed to some linear form. This has been done in the paper by applying suitable transformations to a polynomialy=1+ABx/x
such that it has been brought down to some simpler derivative/equivalent in a linear form of the type y′=a+px′
The rheological implications of the linear relation, vis-a-vis its polynomial parent, have been interpreted and the role of ductile strain and rheology on the overall shape/geometry of the natural folds during various stages of folding has been discussed.
