Title: Folds and the strain ellipsoid: a general model
Abstract: A new general model is proposed to account for non-orthogonal relationships of fold axes and axial surfaces to the axes of the finite strain ellipsoid. Descriptions in the literature of such relationships, e.g. plunge variations and transecting cleavage, are reviewed and the development of the model is outlined. The model is described, in which plane strain (k′ = 1) or slight flattening strain (k′ = 0.71) or slight constrictional strain (k′ = 1.85) are imposed on a suite of layers with oblique orientations to the bulk strain axes (X >Y >Z). Folds will initiate perpendicular to the direction of shortening in the layer and develop as non-material lines moving through the layer by angular migration. At geologically realistic finite strains the folds will be transected by XY (cleavage). In slight flattening strain, folds are likely to be cylindroidal with axes not measurably oblique to XY. In slight constrictional strain, en-echelon periclines are predicted, with marked transection by cleavage: in some examples the interference of two directions of folding will give rise to severe plunge variations and even downward-facing. Although strain markers frequently indicate finite strains in the flattening field, this may result from the superimposition of slightly constrictional tectonic strain on compactional flattening.
Publication Year: 1981
Publication Date: 1981-01-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 119
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