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Foliation in geology refers to repetitive layering in metamorphic rocks. [1] Each layer can be as thin as a sheet of paper, or over a meter in thickness. [ 1 ] The word comes from the Latin folium , meaning "leaf", and refers to the sheet-like planar structure. [ 1 ]
A fold axis "is the closest approximation to a straight line that when moved parallel to itself, generates the form of the fold". [2] (Ramsay 1967). A fold that can be generated by a fold axis is called a cylindrical fold. This term has been broadened to include near-cylindrical folds. Often, the fold axis is the same as the hinge line. [3] [4]
Fold mountains form in areas of thrust tectonics, such as where two tectonic plates move towards each other at convergent plate boundary.When plates and the continents riding on them collide or undergo subduction (that is – ride one over another), the accumulated layers of rock may crumple and fold like a tablecloth that is pushed across a table, particularly if there is a mechanically weak ...
Generally the axial plane foliation or cleavage of a fold is created during folding, and the number convention should match. For example, an F 2 fold should have an S 2 axial foliation. Deformations are numbered according to their order of formation with the letter D denoting a deformation event. For example, D 1, D 2, D 3. Folds and foliations ...
The foliations are symmetrically arranged with respect to the axial plane, depending on the composition and competency of a rock. For example, when mixed sandstone and mudstone sequences are folded during very-low to low grade metamorphism, cleavage forms parallel to the fold axial plane, particularly in the clay-rich parts of the sequence. In ...
Illustration of mountains that developed on a fold that thrusted. Mountain formation occurs due to a variety of geological processes associated with large-scale movements of the Earth's crust (tectonic plates). [1] Folding, faulting, volcanic activity, igneous intrusion and metamorphism can all be parts of the orogenic process of mountain ...
Possible modes of formation of monoclines. Monoclines may be formed in several different ways (see diagram) By differential compaction over an underlying structure, particularly a large fault at the edge of a basin due to the greater compactibility of the basin fill, the amplitude of the fold will die out gradually upwards.
A detachment fold can evolve into a forced fold when shortening stress exceeds the maximum strength of rock, and as a result the decollement may propagate upwards towards the anticlinal core and fault the detachment fold. [24] The resultant structure poses characteristics of both detachment fold and fault propagation fold. [27]