Geometrical classification of multilayered folds |
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| Institution: | 1. Marine Conservation Society, Ross-on-Wye, Herefordshire, UK;2. Laurence Mee Centre for Society and the Sea, Scottish Association for Marine Science (SAMS), University of the Highlands and Islands, Oban, Scotland, UK;3. Centre for Mountain Studies, Perth College, University of the Highlands and Islands, Scotland, UK;4. Community Voice Consulting, Warrenton, NC, USA;5. Sussex Inshore Fisheries and Conservation Authority, Shoreham, West Sussex, UK;1. Korea Polar Research Institute, Incheon 21990 South Korea;2. Department of Ocean Sciences, Inha University, Incheon 22212 South Korea;3. Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden;4. Korea Institute of Ocean Science and Technology, Ansan 15627 South Korea;5. School of Earth and Environmental Sciences, Seoul National University, Seoul 08826 South Korea;1. Department of Geography, Memorial University, St John''s, NL, Canada;2. Marine Affairs Program, Dalhousie University, Halifax, Nova Scotia, Canada;1. University of Exeter, Exeter, United Kingdom;2. Instituto Universitário de Lisboa (ISCTE-IUL), Cis-IUL, Lisboa, Portugal |
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| Abstract: | A new classification scheme based on the degree of fluctuation in the geometry of different layers of a multilayered fold is suggested. The classification scheme uses the degree of fluctuation in geometry in terms of the standard deviation (σn) of the thickness parameters tα′ (orthogonal thickness parameter) and Tα′ (axial plane parallel thickness parameter) for n number of layers, and dip angle α. The degree of fluctuation in the geometry of a multilayered fold can be represented by σn(tα′) or σn(Tα′) versus α plots on a Cartesian plane. In the proposed classification scheme, multilayered folds have been divided into two broad categories, namely `isodeviatoric' and `anisodeviatoric'. Isodeviatoric folds have a constant fluctuation in the geometry of different layers recorded in terms of σn(tα′) or σn(Tα′) for α>10°. A special type of isodeviatoric fold is recognised as `analogous fold' in which each layer exhibits identical geometry σn(tα′) or σn(Tα′)=0]. Plots of isodeviatoric folds lie parallel to the abscissa (α) and those of analogous folds lie along the abscissa in the σn(tα′) or σn(Tα′) (ordinate) versus α (abscissa) diagram. Analogous folds have been divided into ten varieties (1A1, 1A2, 1A3, 1B, 1C, 2, 3A, 3B, 3C and composite-analogous types). The anisodeviatoric folds do not exhibit constant fluctuation (deviation) in the geometry of different constitutive layers. Such folds have been subdivided into `peri-analogous', `sub-analogous', `sub-non-analogous', `non-analogous' and `strongly non-analogous' types. This classification scheme is applied to folds developed in low-grade metasedimentary rocks of the Mahakoshal Group and low- to medium-grade rocks of the Chhotanagpur Granite Gneiss Complex in central India. |
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