A CLASSIFICATION OF FOLDS : ROLE OF AXIAL ANGLE AND THICKNESS RATIO
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概要
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Geometric parameters/features of folds play a major role in classifying the folds in several ways as well as in making any systematic and comparative study of the various fold types in a structurally deformed terrain. The following parameters of fold geometry enable a simple classification of single-layer, symmetric, natural folds : thickness ratio (R), i.e. the ratio existing between the hinge thickness and the limb thickness ; axial angle (α) which is the angle for a given (outer or inner) trace or arc of a fold as subtended at the apex (hinge), and outer axial angle (α_o) and inner axial angle (α_i) which are the acute angles subtended by the outer and inner arcs respectively at the apex (hinge). Folds which are assumed to have initiated by buckling and have undergone thickening at the hinges are thus considered here as T (thickened) folds. Folds showing uniform layer thickness and with both the outer (α_o) and inner (α_i) axial angles of equal value constitute P (parallel) folds, while those in which the hinge thickness is less than the limb thickness-and therefore the inner axial angle ((α_i) is smaller than the outer one (α_o) - constitute S (supratenuous) folds. Folds which practically do not show any geometric relation between the above parameters constitute F (flow) folds that may form from any of the above (T, P or S) fold types at later/advanced stages of deformation. Each of these four types of folds thus show some definite values/conditions of the above-mentioned geometric parameters : for P-folds, T=1, α_o=α_i ; for T-folds, T>1, α_o<α_i ; for S-folds, T<1, α_o>α_i, while for F-folds, no definite geometric relations amongst the above parameters exist.
- 日本情報地質学会の論文
- 2005-03-25
著者
関連論文
- A CLASSIFICATION OF FOLDS : ROLE OF AXIAL ANGLE AND THICKNESS RATIO
- ROTATION OF LINEAR STRUCTURES IN SHEAR REGIME: IDENTIFICATION OF SOME QUANTITATIVE SHEAR PARAMETERS