UNIVERSITY OF MYSORE
DEPARTMENT OF STUDIES IN
EARTH SCIENCE
SUBJECT: BASICS OF EARTH SCIENCE
TOPIC: ROCK DEFORMATION
PRESENTED TO:
DARSHAN
FACULTY
UNIVERSITY OF
MYSORE
ROCK DEFORMATION
Structural Geology
ROCK DEFORMATION:
A process of changing or transformation of rocks
due to stress and heat.
Within the Earth rocks are continually being
subjected to forces that tend to bend them, twist
them, or fracture them. When rocks bend, twist
or fracture we say that they deform (change
shape or size). The forces that cause deformation
of rock are referred to as stresses (Force/unit
area). So, to understand rock deformation we
must first explore these forces or stresses.
If stress is not equal from all
directions then we say that
the stress is a differential
stress.
Three kinds of differential stress
occur.
1. Tensional stress (or extensional
stress), which stretches rock;
2. Compressional stress, which
squeezes rock; and
3. Shear stress, which result in
slippage and translation.
STAGES OF DEFORMATION:
When a rock is subjected to increasing
stress it passes through 3 successive stages
of deformation.
• Elastic Deformation - wherein the strain
is reversible.
• Ductile Deformation - wherein the strain
is irreversible.
• Fracture - irreversible strain wherein the
material breaks.
We can divide materials into two classes that
depend on their relative behavior under stress.
• Brittle materials have a small or large region of elastic behavior
but only a small region of ductile behavior before they fracture.
• Ductile materials have a small region of elastic behavior and a
large region of ductile behavior before they fracture.
How a material behaves will depend on
several factors. Among them are:
• Temperature - At high temperature molecules and their bonds can stretch and move, thus materials will
behave in more ductile manner. At low temperature, materials are brittle.
• Confining Pressure - At high confining pressure materials are less likely to fracture because the pressure
of the surroundings tends to hinder the formation of fractures. At low confining stress, material will be
brittle and tend to fracture sooner.
• Strain rate - At high strain rates material tends to fracture. At low strain rates more time is available for
individual atoms to move and therefore ductile behavior is favored
• Composition - Some minerals, like quartz, olivine, and feldspars are very brittle. Others, like clay
minerals, micas, and calcite are more ductile. This is due to the chemical bond types that hold them
together.
TYPES OF DEFORMATION:
1.FOLDS
2.FAULTS
3.JOINTS
FOLDS:
Flat lying sedimentary & volcanic rocks are often
bent into a series of wave-like undulations.
TYPES OF FOLDS:
1. Anticline: linear, strata normally dip away from axial
center, oldest strata in center.
2. Syncline: linear, strata normally dip toward axial center,
youngest strata in center.
3. Antiform: linear, strata dip away from axial center, age
unknown, or inverted.
TYPES OF FOLDS:
FAULTS:
A fault is a fracture or zone of fractures between
two blocks of rock. Faults allow the blocks to move
relative to each other.
TYPES OF FAULTS:
• Normal (extensional) faults
• Reverse or thrust (compressional) faults
• Strike-slip (shearing) faults.
TYPES OF FAULTS:
JOINTS:
Joint, in geology, a brittle-fracture surface in rocks along which
little or no displacement has occurred. Present in nearly all
surface rocks, joints extend in various directions, generally
more toward the vertical than to the horizontal.
TYPES OF JOINTS:
• Non systematic joints
• Systematic joints
• Columnar jointing
THANK YOU ALL.
PRESENTED BY:
BHOOMIKA.R
1ST M.COM ‘B’
(Open Elective Student)
UNIVERSITY OF MYSORE.
