Coeval boudinage and folding of oblique single layers under coaxial plane strain: Layer rotation around the principal stretching axis (X). (December 2020)

• Record Type: Journal Article
• Authors: Zulauf, J.; Zulauf, G.; Hattingen, E.
• Is Part Of: Journal of structural geology. Volume 141(2020)
• Publication Date: 2020-12
• Subjects: Coeval folding and boudinage -- Plane strain -- Deformation oblique layer -- Analogue modelling; Geology, Structural -- Periodicals; Géomorphologie structurale -- Périodiques; Geology, Structural; Periodicals; 551.805
• DOI: 10.1016/j.jsg.2020.104217
• Languages: English
• ISSNs: 0191-8141

Abstract

Abstract: We carried out scaled analogue modelling to show the influence of varying layer obliquity on the geometry of single-layer folds and boudins, which developed simultaneously under coaxial plane strain. The initial angle ( θ Z(i) ) between the competent layer and the shortening axis ( Z ) was gradually changed by turning the layer around the principal stretching axis ( X ). Although oblique-layer rotation was similar fast like that of a corresponding passive plane, each layer was crossing different strain fields (shortening, reduced shortening, elongation) resulting in coeval boudinage and F1-folding, the latter with fold axes parallel to X . A rise in θ Z(i) led to increase of boudinage and decrease of F1-folding. The amplitude of F1-folds increased with viscosity ratio between layer and matrix but was hardly affected by θ Z(i) . The arc- and wavelength of F1-folds, on the other hand, increased if θ Z(i) > 45°. In cases of low viscosity ratio between layer and matrix, boudins were affected by F2-folds with axes subperpendicular to the layer. Both F1- and F2-folds show increasing interlimb angles at rising θ Z(i) . The structures of the present study are largely not cylindrical and require investigation in three dimensions. They are frequent in high-pressure/low-temperature metamorphic rocks of subduction-zone settings and in salt walls. Highlights: Rotation of single layers around the X-axis led to coeval boudinage and folding. During progressive strain, the competent layer rotates like a passive plane. Boudins are affected by F2-folds with axes perpendicular to the layer. Real 3D structures were produced under bulk coaxial plane strain.