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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).
Topographic map showing detachment folds in the eastern Sichuan Basin, China.. A detachment fold, in geology, occurs as layer parallel thrusting along a decollement (or detachment) develops without upward propagation of a fault; the accommodation of the strain produced by continued displacement along the underlying thrust results in the folding of the overlying rock units.
In his original use of the term, however, he did, in fact, use the up-dip direction of the fold. 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.
For economic geology such as petroleum and mineral development, as well as research, modeling of structural geology is becoming increasingly important. 2D and 3D models of structural systems such as anticlines, synclines, fold and thrust belts, and other features can help better understand the evolution of a structure through time.
In a fold-thrust belt, the décollement is the lowest detachment [1] (see Fig 1.) and forms in the foreland basin of a subduction zone. [1] A fold-thrust belt may contain other detachments above the décollement—an imbricate fan of thrust faults and duplexes as well as other detachment horizons. In compressional settings, the layer directly ...
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. [1] By mild reactivation of an earlier extensional fault during a phase of inversion causing folding in the overlying sequence. [2]
Chevron folds with flat-lying axial planes, Millook Haven, North Cornwall, UK. Chevron folds are a structural feature characterized by repeated well behaved folded beds with straight limbs and sharp hinges. Well developed, these folds develop repeated set of v-shaped beds. [1] They develop in response to regional or local compressive stress.
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 ...