Vergence (geology)

In structural geology, vergence refers to the direction of the overturned component of an asymmetric fold.

The earliest form of use, and the recognized introduction to the term vergence, came from the German geologist, Hans Stille, in 1924.

In this sense, the term vergence, has implications of movement and, thus, has become controversial in geology, because vergence, in Stille's original definition, only describes geometrical relationships, and many geologists believed it should not be used as a primary tool for describing movement.

As a result of this controversy, the use of the term never reached international agreement, and consequently has been used in distinctly different ways, throughout history.

The main reason this creates confusion is a result of the common definition of fold-facing in geology, which is described as the direction (normal to the axis of a fold and corresponding to the axial plane) that points towards younger beds.

Based on this independence, much of the confusion has been cleared up, and both concepts of vergence and facing are of important use to geologists, especially in the analysis of more complex structures.

These phrases can be used in conjunction with one another to describe the geometric aspects of the shape and direction of the fold.

[4] One of the main applications of vergence in geology is the tool it provides geologists to describe the geometries of folds on a small scale.

[2][3] One of the most important uses of vergence is that it gives geologists a sense of the geometric property of symmetry in folds.

This can result in inaccuracies in determining the geometries of folds, and therefore affect the mapping of larger areas.

In areas of simple deformation, vergence can even be used as a tool to locate hinge zones of major folds, as well as the sense of shear.

[6] Using vergence as a tool to map out larger zones, should be used with caution in more complex areas where there have been multiple deformations.

Overall, vergence provides a very useful tool to geologists in determining the components of larger-scale areas and structures.