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Structural Analysis of Orogenic Belts |
Department of Geology, Trinity College, Dublin 2, Ireland
Department of Electronic Engineering, Trinity College, Dublin 2, Ireland
The construction of sections is essential to the analysis of rock bodies. Qualitative sketch sections and block diagrams help to unravel stratigraphy within complex polyphase structures. They also provide a method of summarizing information. Present methods of constructing quantitative sections, being only applicable to parallel folds, are of limited value.
A new method of constructing quantitative sections is described. In this the rate of change of fold shape with depth is measured, rather than assumed as previously. On profile sections of folds, this rate can be described by constructing stratification isogonal lines joining points of constant dip. Their orientation can be used to classify folds. In cylindrical folds, such isogonal lines lie upon stratification isogonal surfaces, the location of which can be found from structural maps, either by graphic construction, or by using a digitizer and an electronic computer. This information is used to construct, on any section plane, stratification isogonal lines which sub-divide the section into dip zones, and provide control for constructing sections to the depth of topographic or structural relief.
Applications of the method to recognizing faults and palaeoslopes, and to classifying folds and constructing sections in areas of noncylindrical and polyphase deformation, are described.
These methods make fuller use of structural data and provide quantitative descriptions of folds. This could lead to the definition of structural facies and to a better understanding of displacements within the continental crust.
