page_title: Vergence (geology)
section_title: Understanding Vergence in Folds
hierarchical_section_title: Vergence (geology) / Understanding Vergence in Folds
caption_attribution_description: English: A small rock fold, taken on a rocky beach on Holy Island, Wales.
context_page_description: In structural geology, vergence refers to the direction of the overturned component of an asymmetric fold. In simpler terms, vergence can be described as the horizontal direction in which the upper-component of rotation is directed. Vergence can be observed and recorded in folds to help a geologist determine characteristics of larger fold areas. Vergence is used to provide an overall characterization, in the symmetry of folds, and can be used to observe changes in small-scale structures in relation to the axis of a large fold. The vergence of a fold lies parallel to the surrounding surfaces of a fold, so if these surrounding surfaces are not horizontal in nature, the vergence of the fold will be inclined. For a fold, the direction, as well as the extent to which vergence occurs, can be calculated from the strike and dip of the axial surfaces, along with that of the enveloping surfaces. These calculations can be very useful for geologists in determining the overall elements of larger areas.
context_section_description: One of the main uses of vergence is to give an idea to the overall geometry of a fold by describing the symmetry or asymmetry of a fold. To better understand the importance of this use, it is important to understand the different classifications of folds, based on their geometry. The most commonly used terms to describe and classify folds, based on their geometry, are the terms antiforms and synforms, as well as anticlines and synclines. Although these terms sound similar, they mean very different things in reference to the geometry of a fold.
  When the limbs of a fold converge upward, the fold is referred to as an antiform. Conversely, when the limbs of a fold converge downward, the fold is known as a synform. Not to be confused with these terms (antiform and synform), the terms anticline and syncline are used in description of the stratigraphic significance of the fold. These phrases can be used in conjunction with one another to describe the geometric aspects of the shape and direction of the fold.
  In addition, folds can be referred to as either symmetrical or asymmetrical. When a group of folds, whose axial planes are found to be perpendicular to the plane representing the enveloping surface of the folds (plane drawn tangential to the folds), the folds are considered symmetrical. When this is not the case, the folds are considered asymmetrical, and the asymmetry of these folds will vary systematically across the axial surfaces of the folds. Vergence can be used to, not only give an overall idea of the symmetry (or asymmetry) of a fold, but in the common case of asymmetric folds, it can be used to record the previously mentioned systematic variation of asymmetry of folds. This is very important to the use of vergence in the field for geologists when determining the micro-to-macro components of an area.
caption: Small-scale rock folding
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