Plastic deformation of rocks and rock-forming minerals. When a rock or mineral is subjected to stress, stress is proportional to strain as long as the elastic limit has not been exceeded. This relationship is known as Hooke's law. Many rocks in orogenic belts show evidence of having been deformed plastically. In this video lesson, you will learn about how rock can be deformed from stress and the effect this has on the rock. You will identify different types of deformation. Deformation of Rocks. Rock Deformation. ▫ Large scale deformation of the. Earth's crust = Plate Tectonics. ▫ Smaller scale deformation = structural geology.


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Here, rocks are squeezed together, like a car caught in the middle of a long pile-up on the highway. Shear stress is when rock slips in a horizontal direction.

Stress and Strain - Rock Deformation

With shear stress, the rock is being pulled in opposite directions but on different ends. To understand this, try putting your palms together and then rubbing them back and forth.

Now imagine that there is a rock in the middle and you can see how one end goes forward while the other end gets pulled backward. Stages of Rock Deformation As rocks are stressed, they go deformation of rocks stages of deformation.

At first, the rock is strained enough that its shape or size may change, but the change is reversible.

This is the first stage, called elastic deformation. Think of this 'elastic' change like the elastic in your waistband.

Geological Society - Deformation of Rocks

If you pull it and then let it go, the stretch is reversible deformation of rocks it can go back to its original shape. Rock beneath the Earth's surface experiences equal pressure exerted on it from all directions because of the weight of the overlying rock. It is like the hydrostatic stress water pressure that a person feels pressing all around their body when diving down deep in water.


In many cases, rock may experience an additional, unequal stress due to tectonic forces. The limbs intersect at the tightest part of the fold, called the hinge.

A line connecting all points on the hinge is called the fold axis. An imaginary plane that includes the fold axis and divides the fold deformation of rocks symmetrically as possible is called the axial plane of the fold.

We recognize several different kinds of folds.

Deformation of Rocks

Monoclines are the simplest types of folds. Monoclines occur when horizontal strata are bent upward so deformation of rocks the two limbs of the fold are still horizontal.

Anticlines are folds where the originally horizontal strata has been folded upward, and the two limbs of the fold dip away from the hinge of the fold.

  • Deformation of Rock
  • Rock Deformation: Causes and Types - Video & Lesson Transcript |
  • Stress and Strain - Rock Deformation

Synclines are folds where the originally horizontal strata have been folded downward, and the two limbs of the fold dip inward toward the hinge of the fold.

Synclines and anticlines usually occur together such that the limb of a syncline is also the limb of an anticline. In the diagrams above, the fold axes are horizontal, but if the fold axis is not horizontal the fold is called a plunging fold and the angle that the fold axis makes with a horizontal line is called the plunge of the fold.

Note that if a plunging fold intersects a horizontal surface, we will see the pattern of the fold on the surface see also figures Domes and Basins are formed as a result of vertical crustal motion. Domes look like an overturned bowl and deformation of rocks from crustal upwarping.

Rock Deformation: Causes and Types

Basins look like a bowl and result from subsidence see figure Folds are described by the severity of folding.

Further classification of folds include: If the two limbs of the fold dip away from the axis with the same angle, the fold is said to be a symmetrical fold. If the limbs dip at different angles, the folds are said to be asymmetrical folds.

If the compressional stresses that cause the folding are intense, the fold can close up and have limbs that are parallel to each other. Such a fold is called an isoclinal fold iso means same, deformation of rocks cline means angle, so isoclinal means the limbs have the same angle.