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In structural geology, a fold is a stack of originally planar surfaces, such as sedimentary strata, that are bent or curved ("folded") during permanent deformation. Folds in rocks vary in size from microscopic crinkles to mountain-sized folds. They occur as single isolated folds or in periodic sets (known as fold trains).
C i (equivalent to S 2) – inversion symmetry; C 2 – 2-fold rotational symmetry; C s (equivalent to C 1h and C 1v) – reflection symmetry, also called bilateral symmetry. Patterns on a cylindrical band illustrating the case n = 6 for each of the 7 infinite families of point groups. The symmetry group of each pattern is the indicated group.
A high-index reflective subgroup is the prismatic octahedral symmetry, [4,3,2] (), order 96, subgroup index 4, (Du Val #44 (O/C 2;O/C 2) *, Conway ± 1 / 24 [O×O].2). The truncated cubic prism has this symmetry with Coxeter diagram and the cubic prism is a lower symmetry construction of the tesseract, as .
These axes are arranged as 3-fold axes in a cube, directed along its four space diagonals (the cube has 4 / m 3 2 / m symmetry). These symbols are constructed the following way: First position – symmetrically equivalent directions of the coordinate axes x, y, and z. They are equivalent due to the presence of diagonal 3-fold axes.
In geology, 3D fold evolution is the study of the full three dimensional structure of a fold as it changes in time. A fold is a common three-dimensional geological structure that is associated with strain deformation under stress .
The vergence of a fold can help a geologist determine several characteristics of folding on a larger scale, including the style, position, and geometry of the folding. [ 3 ] By observing vergence in a fold, geologists can record data that can be used to calculate the approximate position and geometry of a larger area, and therefore assist ...
The thin-skinned style of deformation is typical of many fold and thrust belts developed in the foreland of a collisional zone or back arc of a continental volcanic arc. This is particularly the case where a good basal decollement exists, usually in a weaker layer like a shale , evaporite , or a zone of high pore fluid pressure. [ 2 ]
S 2n (for Spiegel, German for mirror) denotes a group with only a 2n-fold rotation-reflection axis. D n (for dihedral, or two-sided) indicates that the group has an n-fold rotation axis plus n twofold axes perpendicular to that axis. D nh has, in addition, a mirror plane perpendicular to the n-fold axis.