Types of Folds, Parts, Features, Diagram, Fold Mountains

Types of Folds

A fold is a wave-like undulating structure formed when rocks or a portion of the earth’s crust is folded (deformed by bending) under compressional stress. The folds are composed of several strata (rock layers). The upwardly convex folds are referred to as anticlines. The older strata form the core (centre) of an anticline fold, and the younger strata extend outwards.

Synclines, on the other hand, are downwardly convex folds. The younger strata form the core of a syncline fold, and the older strata extend outwards. When two or more of the Earth’s tectonic plates collide, fold mountains form. (This is why Fold Mountains, formed by sedimentary rocks, are typically found near continent boundaries.)

As a result of compression, rocks and debris are distorted and folded into rocky outcrops, hills, mountains, and entire mountain ranges.

They form at plate boundaries that converge, also known as continental collision zones or compression zones. At a compression zone, tectonic activity forces crustal compression at the leading edge of crust formation. As a result, the majority of fold mountains are found on or near the margins of continental plate boundaries.

Read More: Geomorphic Processes

Folds Meaning

The crustal rocks are subjected to the compressional force generated by the horizontal movement of the plates. The rocks under this force form wavy undulations called folds.

Parts of a Folds

The following are the parts of the fold:

Read More: Plate Tectonics Theory

Types of Folds

The Type of Folds formed depends on various factors such as the nature of the rock, the intensity of the compressional force, etc. Different folds have been recognized based on structure, appearance, and geometry. They are as follows:

1. Symmetrical

These are folds where the axial plane is vertical and both limbs incline uniformly. They are formed when compressive forces regularly act with moderate intensity.

2. Asymmetrical Folds

They are folds where the axial plane is inclined and the limbs of the anticline dip in opposite directions. One limb is longer with a moderate inclination, while the other is shorter with a steep inclination.

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3. Overturned Fold

It is a type of fold where the axial plane is inclined and both limbs dip in the same direction but at different angles.

4. Isoclinal Folds

These are folds where two limbs dip at equal angles in the same direction. They are formed when the compressional forces are so strong that the limbs become parallel.

5. Recumbent Fold

Recumbent folds are characterised by a horizontal axial plane. They are formed when compressive forces are so strong that the limbs become parallel and horizontal. Such recumbent folds are widely found in the Alps.

Read More: Continental Drift Theory

6. Chevron

These are folds with sharp and angular crests and troughs.

7. Fan Fold

When the limbs of a fold are overturned to such an extent that it looks like a fan, it is called a fan fold.

8. Open Fold

Folds, where the angle between two limbs is usually greater than 90 degrees but less than 180 degrees, are called open folds. The rock beds have the same thickness throughout the fold in such folds. They are formed due to moderate compressional force.

9. Closed Fold

Folds, where the angle between two limbs is less than 90 degrees, are called closed folds. The rock beds are thinner at the limbs and thicker at the crests and troughs. They are formed by intensive compressional force.

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10. Nappe

These folds result from complex folding mechanisms due to intense horizontal movement and high compressional forces. They are formed from recumbent folds. The crest of recumbent folds is weak and has cracks. When there is further intense compressional force, one limb of the fold slides forward and overrides the other. Such features are called Nappes. Several nappies are found in the Alps mountains.

11. Anticlinorium

An anticlinorium is formed when there is a series of minor anticlines and synclines within one extensive anticline.

12. Synclinorium

A synclinorium is formed when there is a series of minor anticlines and synclines within one extensive syncline.

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Types of Folds Diagram

Here is a Diagram for Different Types of Folds:

Read More: Types of Rocks

Fold Mountains

When two or more of the Earth’s tectonic plates collide, fold mountains form. This is why Fold Mountains, formed by sedimentary rocks, are typically found near continent boundaries. As a result of compression, rocks and debris are distorted and folded into rocky outcrops, hills, mountains, and entire mountain ranges.

They form at plate boundaries that converge, also known as continental collision zones or compression zones. At a compression zone, tectonic activity forces crustal compression at the leading edge of crust formation. As a result, the majority of fold mountains are found on or near the margins of continental plate boundaries.

Rocks near the continental crust’s edge are frequently weaker and less stable than rocks near the continent’s centre. As a result, they are more prone to folding and warping.

The majority of fold mountains are composed of sedimentary and metamorphic rock formed under high pressure and low temperatures. Many fold mountains form when an underlying layer of ductile minerals, such as salt, is present.

Read More: Important Mountain Passes in India

Types of Folds UPSC

A uniform framework for comprehending mountain-building processes, volcanic eruptions, earthquakes, the evolution of the Earth’s surface, and reconstructing the planet’s former continents and oceans was provided by the plate tectonics theory, which deals with the dynamics of the lithosphere, the outer shell of the planet. A UPSC aspirant should be well aware of the topic of how various changes happen inside and over the surface of the earth. The details in the article would help candidates prepare for UPSC 2023.

Other Indian Geography Topics

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