NIT RAIPUR APPLIED GEOLOGY

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BRITTLE DEFORMATION
ITS MECHANISM AND KINEMATICS
SUBMITTED BY:
NAME: GAURAB DEB
ROLL NO: 22225007
SUB: GEOLOGCAL FIELD TRAINING
CLASS: MTECH 2nd SEMESTER

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CONTENTS
 INTRODUCTION
 MECHANISM
 KINEMATICS
 SOME EXAMPLES, FROM SONAKHAN REGION

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INTRODUCTION
 Brittle deformation is a type of deformation that occurs in rocks and other materials
when they are subjected to stress beyond their strength limit, which result in the
formation of cracks and fractures
 The process is characterized by an irreversible failure of the material, without any
significant plastic deformation.
 Brittle deformation mainly occurs along discrete planes in the rocks, instead of
involving the whole rock body.
 Examples: Faults, Fractures, etc.

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Mechanism of Brittle Deformation
 The mechanism of brittle deformation is controlled by the behavior of the
material’s microstructures , which includes the arrangement of grains, mineral
phases, etc.
 When an external force is applied to a material, the stress is transmitted through
the microstructures, causing the weakest points to fail first, and subsequently leading
to the formation of cracks and fractures.
The brittle deformation process occurs/proceed in three stages:
Elastic Deformation
Yield Point
Fracture Point

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Mechanism : Elastic Deformation
 It is the first stage of deformation; where the materials deforms under stress, but
can returns to its original shape when the stress is removed.
In this stage, the deformation is reversible and does not cause any permanent
changes in the rock body.
 Elastic deformation causes the chemical bonds of the substance to undergo
stretching and bending.
 Here, atoms do not slip pass on each other.
 Examples: stretching a rubber band.

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MECHANISM: YIELD POINT
 As the stress on the material increases; it reaches a point where it exceeds the
strength limit of the material, leading to the onset of plastic deformation.
 This point is also known as point of Elastic limit.
 Here the materials begins to deform permanently, causing some of the grains to
rotate and slip past each other.
 This stage of deformation is irreversible and causes permanent changes in the
material.
 Example: If a steel rod is subjected to increasing levels of stress, it will begin to
elongated elastically unit it reaches its elastic limit.

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 Here the deformation is of plastic behavior , and it gives a change in the
morphology/shape of the rock mass.
 Example: Folds.

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MECHANISM: FRACTURE POINT
 The stress on the material exceeds its ultimate strength, resulting in the formation
of cracks in the rock mass.
 The point at which failure occurs in a rock mass is known as the failure point.
 The failure point is a critical parameter in the design and engineering of structures
and materials.
 Example: Formation of faults in a rock.

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KINEMATICS OF BRITTLE DEFORMATION
 The kinematics of brittle deformation refers to the study of geometric
changes that occur in a rock or other material when it undergoes brittle
deformation. This involves the analysis of the deformation patterns, the
geometry of the fractures and faults, and the displacement of rock masses.
 Understanding the kinematics of brittle deformation is important in the
interpretation of geological structures and the prediction of the behavior of
rock masses under stress.
 The kinematics of brittle deformation can be studied at different scales,
ranging from the microscopic scale of individual grains and crystals, to the
macroscopic scale of entire rock masses

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MICROSCOPIC SCALE
 The kinematics of brittle deformation is characterized by the formation and
propagation of micro cracks through the material.
 These cracks are initiated at weak points in the material, such as grain boundaries
or mineral interfaces, and propagate through the material as the applied stress
increases.
 The orientation and spacing of these micro cracks depend on the orientation and
strength of the applied stress, and the nature of the microstructure.
fig: presence of joints within a granitic rock, in
a microscopic scale (PPL)

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MESOSCOPIC SCALE
 The mesoscopic scale, the kinematics of brittle deformation is characterized by the
formation of fractures and faults within the rock mass.
 These fractures are typically planar or linear features, and their orientation and
geometry depend on the orientation and nature of the applied stress, as well as the
mechanical properties of the rock mass.
 The displacement of rock masses along fractures and faults can also be studied
using kinematic analysis techniques, such as the measurement of fault slip rates and
the analysis of fault surface morphology.

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Thank You