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Geology · 300 Level
This is the complete lecture note for GEY 313 GEY-313 Structural Geology, prepared for Geology students at 300 Level. You can read it online below, open it in the full viewer, or download the PDF for offline study. It pairs with the course's video lectures, so you can read and watch together.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Course code: GEY 313 Course title: Structural Geology Units: 3 Units List of series Series 1: Fundamentals of Rock Dynamics and Stress-Strain Relationships Series 2: Faults, Folds, Shears, and Ring Dykes Series 3: Introduction to Crustal Tectonics and Deformational Structures Series 4: Geological Map Study, Problems, and Interpretation Series 5: Stereographic Projection and Structural Mapping Practice 1.1 Dynamics of Rocks - 1.1.1 Definition and scope of rock dynamics - 1.1.2 Physical properties of rocks influencing deformation - 1.1.3 Behaviour of rocks under different environmental conditions 1.2 Stress in Rocks - 1.2.1 Definition of stress - 1.2.2 Types of stress: compressional, tensional, shear - 1.2.3 Measurement and representation of stress in geology 1.3 Strain in Rocks - 1.3.1 Definition of strain - 1.3.2 Types of strain: elastic, plastic, brittle - 1.3.3 Factors controlling strain behaviour 1.4 Stress-Strain Relationships - 1.4.1 Stress-strain curves and their geological significance - 1.4.2 Elastic limit, yield point, and fracture point - 1.4.3 Geological implications of stress-strain behaviour
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS 1.5 Applications in Structural Geology - 1.5.1 Role of stress-strain analysis in understanding faults and folds - 1.5.2 Importance in crustal deformation studies - 1.5.3 Practical examples in geological mapping Introduction Rocks form the very foundation of the earth’s crust, yet they are far from static. They respond to forces acting upon them, sometimes bending gently and at other times breaking abruptly. Understanding how rocks behave under different conditions is essential for interpreting the structures we see in the field, such as folds, faults, and fractures. This Series introduces you to the fundamental principles of rock dynamics and stress-strain relationships, which are central to the study of structural geology and provide the basis for more advanced topics later in the course. The aim of this Series is to equip you with the knowledge and skills to define, explain, and analyse the dynamics of rocks, the nature of stress and strain, and the relationships between them. By the end of this Series, you should be able to evaluate how these concepts apply to geological structures and their interpretation. We shall commence this Series by exploring the dynamics of rocks, focusing on their properties and behaviour under varying conditions. Next, we will examine the concept of stress in rocks, including its types and representation. Following that, we will move on to strain, considering its forms and controlling factors. Subsequently, we will study stress-strain relationships, looking at curves, limits, and their geological implications. Finally, we will wrap up by discussing practical applications of stress-strain analysis in structural geology, particularly in relation to faults, folds, and crustal deformation. Series Learning Outcomes Upon completing this Series, you should be able to: - SLO 1.1 define the concept of rock dynamics and explain the physical properties that influence rock behaviour, - SLO 1.2 describe the nature of stress in rocks and classify its main types, - SLO 1.3 explain the concept of strain in rocks and distinguish between elastic, plastic, and brittle strain behaviours, - SLO 1.4 analyse stress-strain relationships using curves and identify their geological significance, and
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS - SLO 1.5 apply stress-strain principles to evaluate geological structures such as faults, folds, and crustal deformation. 1.1 Dynamics of Rocks 1.1.1 Definition and scope of rock dynamics The study of rock dynamics refers to the examination of how rocks respond to forces and conditions within the earth’s crust. Rock dynamics encompasses the physical behaviour of rocks under stress, including their ability to deform, fracture, or remain stable. This area of study is crucial because it provides the foundation for understanding larger geological structures such as folds, faults, and fractures. When we speak of rock dynamics, we are essentially asking: how do rocks behave when subjected to forces from within the earth? The answer depends on their composition, environment, and the magnitude of the forces applied. Fill in the blank: Rock dynamics is the study of how rocks when subjected to forces within the earth’s crust.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Figure 1.1 Behaviour of rocks under stress. 1.1.2 Physical properties of rocks influencing deformation The physical properties of rocks are the measurable characteristics that determine how rocks respond to stress. These include mineral composition (the types of minerals present and their bonding), texture (the arrangement and size of grains), porosity (the amount of void space), and density (mass per unit volume). For example, rocks with high porosity may deform more easily under stress compared to dense crystalline rocks. Similarly, fine-grained rocks may exhibit different behaviours compared to coarse-grained ones. Fill in the blank: Rocks with high ______ tend to deform more easily under stress compared to dense crystalline rocks.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Rock Property Definition & Examples Influence on Deformation Behavior Composition (Mineralogy) The specific minerals that make up the rock (e.g., Quartz, Calcite, Clays). Strong/Brittle: Minerals with strong covalent/ionic bonds like Quartz and Feldspar resist deformation but fail suddenly (fracture) at low depths. Weak/Ductile: Layers of phyllosilicates (Clays, Micas) or Calcite act as lubricants, allowing for easy folding and flow. Texture The size, shape, and arrangement of grains or crystals (e.g., Clastic vs. Crystalline). Crystalline: Interlocking crystals (Granite) are generally stronger and more brittle. Foliated/Stratified: Planes of weakness (bedding in Shale, foliation in Schist) cause anisotropy, where rocks deform or fail much more easily along those pre-existing surfaces. Porosity The percentage of void space within the rock. Weakening Effect: High porosity (e.g., Sandstone, Vesicular Basalt) significantly reduces a rock's compressive and shear strength. Fluid Influence: Pore spaces often contain water; high fluid pressure reduces "effective stress," triggering brittle failure (faulting) even at great depths. Density The mass per unit volume (governed by mineralogy and porosity). Confining Pressure: Higher density rocks often require greater stress to initiate deformation. Depth Relationship: As density increases with depth (due to compaction and mineral phase changes), rocks transition from brittle behavior to ductile flow. Table 1.1 Selected physical properties of rocks and their influence on deformation. 1.1.3 Behaviour of rocks under different environmental conditions The behaviour of rocks refers to the way they respond to stress depending on environmental factors such as temperature, pressure, and presence of fluids. At low temperatures and pressures, rocks are more likely to break in a brittle manner. At higher temperatures and
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS pressures, they may bend or flow plastically. The presence of fluids often reduces the strength of rocks, making them more susceptible to deformation. This explains why rocks deep within the earth’s crust often show ductile behaviour, forming folds, while those near the surface tend to fracture and form faults. Fill in the blank: At high temperatures and pressures, rocks are more likely to deform in a _____ manner rather than fracturing. Plate 1.1 Comparison of brittle and ductile behaviour of rocks. Pilot questions 1.1 1. Which term refers to the study of how rocks respond to forces within the earth’s crust? 2. Name two physical properties of rocks that influence their deformation. 3. What type of behaviour do rocks exhibit at low temperatures and pressures? 4. How does porosity affect the deformation of rocks?
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS 5. What environmental factor can reduce the strength of rocks and make them more susceptible to deformation? 1.2 Stress in Rocks 1.2.1 Definition of stress In geology, stress is defined as the force applied per unit area within a rock body. It represents the intensity of internal forces acting on rocks due to tectonic movements, gravity, or other geological processes. Stress is a fundamental concept because it determines how rocks deform, whether they bend, break, or flow. Stress is usually expressed in units of pressure, such as pascals, and is considered in terms of direction as well as magnitude. This directional nature makes stress a vector quantity, meaning it has both size and orientation. Fill in the blank: Stress is the force applied per unit within a rock body.
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