Abstract
Folds are spectacular geological structures that are seen in layered rock on many different scales. To mark 30 years of the Journal of Structural Geology, we review the information that can be gained from studies of folds in theory, experiment and nature. We first review theoretical considerations and modeling, from classical approaches to current developments. The subject is dominated by single-layer fold theory, with the assumption of perfect layer-parallel shortening, but we also review multilayer fold theory and modeling, and folding of layers that are oblique to principal stresses and strains. This work demonstrates that viscosity ratio, degree of non-linearity of the flow law, anisotropy, and the thickness and spacing distribution of layers of different competence are all important in determining the nature and strength of the folding instability. Theory and modeling provide the basis for obtaining rheological information from natural folds, through analysis of wavelength/thickness ratios of single layer folds, and fold shapes. They also provide a basis for estimating the bulk strain from folded layers. Information about folding mechanisms can be obtained by analysis of cleavage and fabric patterns in folded rocks, and the history of deformation can be revealed by understanding how asymmetry can develop in folds, by how folds develop in shear zones, and how folds develop in more complex three-dimensional deformations.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 2042-2071 |
| Number of pages | 30 |
| Journal | Journal of Structural Geology |
| Volume | 32 |
| Issue number | 12 |
| DOIs | |
| State | Published - Dec 2010 |
Bibliographical note
Funding Information:We thank Cees Passchier for inviting us to contribute a review paper to mark JSG’s 30th anniversary. It brought us together to write about one of our favorite topics, a happy reminder both of our research begun long ago at Imperial College, London, and of our shared time as former editors of JSG. We would like to thank John Ramsay for inspiring us to appreciate the beauty of folds, and Ray Fletcher for providing keen comments, interest and the sharing of ideas. PJH acknowledges earlier support from the National Science Foundation and support in various forms from the University of Minnesota. SHT acknowledges support for research from the NERC as a Senior Research Fellow and from the University of Manchester, and thanks Jack Treagus for his constant interest and encouragement over the years. Finally, we thank Neil Mancktelow and Sudipta Sengupta for their review comments that have been invaluable in helping us revise the paper.
Keywords
- Deformation history
- Folding
- Folds