Editing Structural geology (section)

==== Plane, fabric, fold and deformation conventions ====
The convention for analysing structural geology is to identify the '''planar structures''', often called ''planar fabrics'' because this implies a [[rock microstructure|textural]] formation, the '''linear structures''' and, from analysis of these, unravel '''deformations'''.

Planar structures are named according to their order of formation, with original sedimentary layering the lowest at S0. Often it is impossible to identify S0 in highly deformed rocks, so numbering may be started at an arbitrary number or given a letter (S<sub>A</sub>, for instance). In cases where there is a [[bedding-plane]] foliation caused by burial metamorphism or [[diagenesis]] this may be enumerated as S0a.

If there are folds, these are numbered as F<sub>1</sub>, F<sub>2</sub>, etc. Generally the axial plane foliation or [[Cleavage (geology)|cleavage]] of a fold is created during folding, and the number convention should match. For example, an F<sub>2</sub> fold should have an S<sub>2</sub> axial foliation.

Deformations are numbered according to their order of formation with the letter D denoting a deformation event. For example, D<sub>1</sub>, D<sub>2</sub>, D<sub>3</sub>. Folds and foliations, because they are formed by deformation events, should correlate with these events. For example, an F<sub>2</sub> fold, with an S<sub>2</sub> axial plane foliation would be the result of a D<sub>2</sub> deformation.

Metamorphic events may span multiple deformations. Sometimes it is useful to identify them similarly to the structural features for which they are responsible, e.g.; M<sub>2</sub>. This may be possible by observing [[porphyroblast]] formation in cleavages of known deformation age, by identifying metamorphic mineral assemblages created by different events, or via [[geochronology]].

Intersection lineations in rocks, as they are the product of the intersection of two planar structures, are named according to the two planar structures from which they are formed. For instance, the intersection lineation of a S<sub>1</sub> cleavage and bedding is the L<sub>1-0</sub> intersection lineation (also known as the cleavage-bedding lineation).

Stretching lineations may be difficult to quantify, especially in highly stretched ductile rocks where minimal foliation information is preserved. Where possible, when correlated with deformations (as few are formed in folds, and many are not strictly associated with planar foliations), they may be identified similar to planar surfaces and folds, e.g.; L<sub>1</sub>, L<sub>2</sub>. For convenience some geologists prefer to annotate them with a subscript S, for example L<sub>s1</sub> to differentiate them from intersection lineations, though this is generally redundant.