Chapter 10. Deformation By: Dwight Dher Ranis Alaba
Deformation • Definition: the changes of rock masses in different sizes, shape, and position. • Crustal deformation mostly occur along plate margins. Force & Stress. • Force tends to put stationary (not moving) objects in motion or change the motion of moving objects. Ex. When your door is stuck (stationary), you apply force to move it (get it in motion. Cont. on next page
Continuation • Structural Geologists use the term “stress” to describe the forces that deforms a rock. • The magnitude of stress also relates to the area on which the force acts, not just the amount of force applied. • Stress causes irreversible damage/change in sizes and shapes of a rock body. Types of Stress • Differential Stress – stress is applied unequally in different directions • Compression stress – plate collides to shorten and thicken the earth’s crust. Cont. on next page
continuation • Tensional stress – stretches horizontally which causes rock bodies to lengthen and thin vertically. • Shear stress – displacement along fault zone or by ductile flow. Strain • Easiest type of deformation that occurs on along small fault surfaces. • Strain shows the effect of stress from the rocks. • There are also different types of stresses. • Elastic deformation, plastic deformation, brittle deformation.
Types of strains • Elastic deformation – rocks return to its original shape when stress is removed. • plastic stress - folding and flowing of stresses in high temperature and pressure causes rocks to deform permanently. • Brittle deformation -