Geometry, description, and properties of rocks Flashcards
1
Q
The branch of geology that deals with:
* Form, arrangement and internal architecture of rocks
* Description, representation, and analysis of structures from the small to moderate scale
* Reconstruction of the motions of rocks
A
Structural Geology
2
Q
____________ provides information about the conditions during regional deformation using structures
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Structural geology
3
Q
- Aims at unraveling the geological context in which deformation occurs.
- Study of the origin and geologic evolution (history of motion and deformation) of large areas (regional to global) of the Earth’s lithosphere (e.g., origin of continents; building of mountain belts; formation of ocean floor)
- this operates at scales ranging from 100 m to 1000 km, and focusses on processes such as continental rifting and basins formation, subduction, collisional processes and mountain building processes etc.
A
Tectonics
4
Q
- Both are concerned with the reconstruction of the motions that shape the outer layers of earth
- Both deal with motion and deformation in the Earth’s crust and upper mantle
- Tectonic events at all scales produce deformation structures
- These two disciplines are closely related and interdependent
A
Tectonics vs. Structural Geology
5
Q
________ is the first stage to any regional geophysical and geochemical surveys aiming at identifying new mineralized provinces. At the mine camp scale, structural geology guide the mining process.
A
Structural geology
6
Q
- ____________ is at the core of geotechnical site assessment for bridges, dams, tunnels, nuclear reactors, waste disposals etc. Because of the obvious relationship between faults and earthquake , structural geology is that core of earthquake prevention and earthquake seismology.
- No geological, geochemical or geophysical study can be done without the input of this.
A
Structural geology
7
Q
Main Principle and Concepts
A
- Original Horizontality
- Uniformitarianism
- Superposition
- Law of Crosscutting Relationships
8
Q
- was proposed by the Danish geological pioneer Nicholas Steno (1638–1686).
- This principle states that layers of sediment are originally deposited horizontally under the action of gravity.
A
Original Horizontality
9
Q
- The principle is important to the analysis of folded and tilted.
- From these observations is derived the conclusion that the Earth has not been static and that great forces have been at work over long periods of time, further leading to the conclusions of the science of plate tectonics; that movement and collisions of large plates of the Earth’s crust is the cause of folded strata.
A
Original Horizontality
10
Q
- This concept, outlined in the very earliest years of geology by James Hutton is the fundamental to the subject.
- It maintains that the process which are occurring presently are the same as those which operated in the past, and that the results of these processes are the same.
A
Uniformitarianism
11
Q
- The earliest of all geological concepts and states that in a series of rock strata, the upper members of the series were formed after the lower members.
- According to the Law of ________, layer 1 was the first layer deposited, and thus the oldest layer. The last layer deposited was layer 12, and thus it is the youngest layer.
A
Superposition
12
Q
- Movements of Earth’s crust can lift up rock layers that were buried and expose them to erosion. Then, if sediments are deposited, new rock layers form in place of the eroded layers. The missing rock layers create a break in the geologic record in the same way that pages missing from a book create a break in a story.
- A break in the geologic record is called an ________. This shows that deposition stopped for a period of time, and rock may have been removed by erosion before deposition resumed.
A
unconformity
13
Q
There are three types of unconformities.
A
- nonconformity.
- angular unconformity .
- disconformity
14
Q
An unconformity in which stratified (layers) of rock rests upon unstratified rock is called a
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nonconformity
15
Q
The boundary between a set of tilted layers and a set of horizontal layers is called an .
A
angular unconformity
16
Q
The boundary between horizontal layers of old sedimentary rock and younger, overlying layers that are deposited on an eroded surface is called a
A
disconformity
17
Q
According to the Law of Superposition, all rocks beneath an unconformity are ____ than the rocks above the unconformity.
A
older
18
Q
- When rock layers have been disturbed by faults (a break or crack in Earth’s crust) or intrusions (a mass of igneous rock that forms when magma is injected into rock and then cools and solidifies), determining relative age may be difficult. In such cases, scientists may apply this.
- is that a fault or intrusion is always younger than all the rocks it cuts through above and below the unconformity.
A
The Law of Crosscutting Relationships
19
Q
________ is study of shapes, arrangements and relationships among rocks and stresses that deform them
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structural geology
20
Q
– is the force applied to a plane divided by the area of the plane and it is what causes rocks to deform
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Stress
21
Q
3 Types of Stress
A
- Compression:pushed together (shortening or flattening)
- Tension:pulled apart (stretching or elongation)
- Shear stress:moved horizontally past each other (smearing)
22
Q
– the result of stress applied to a body, causing deformation of its shape and/or a change in volume
A
Strain
23
Q
When this volume of rock, or some part of it, is forced to change its location or position, it undergoes ____________;
A
translation
24
Q
When this volume of rock, or some part of it, is forced to change its orientation, ____________;
A
rotation
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When this volume of rock, or some part of it, is forced to **change size**, ________;
dilation
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26
When this volume of rock, or some part of it, is forced to **change shape**, __________
distortion
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Types of Rock Deformation (4)
* translation
* rotation
* distortion
* dilation
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____________ of rocks is rather easy to recognize, **analogous to hitting concrete with sledge hammer.** Conditions of stress result in **fracturing or rupturing of rocks**
brittle deformation
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____________ is applied **slowly under constant pressure**, rocks **return to original size and shape** after stress is removed.
elastic stress
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**a set of conditions** must be met before rocks will deform **plastically relative heat, constant pressure, and time.**
Plastic/ductile deformation:
30
* When rocks undergo **permanent plastic/ductile deformation,** a ________ develops.
* When rock undergo **brittle deformation**, a ________ develops.
FOLD; FAULT
31
Factors that affect deformation of rock (4)
1. **Lithostatic Pressure** - weight of overlying rock
2. **Heat** - causes atomic bonds to weaken
3. **Time** - allows stress to be applied slowly or quickly
4. **Composition** - controls rock response to stress(minerals)
32
* Rocks under **high temperature and pressure** tend to undergo ________________ when subjected to a tectonic stress.
deformation without breaking
(plastic/ductile deformation)
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* Rocks under **low temperature and pressure** tend to ____________ when subjected to stress.
fracture (brittle deformation)
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Causes of Rock Displacement/Deformation (4)
1. Tectonic Plate Movement
2. Subduction
3. Volcanic Activity
4. Intrusive Igneous Activity
35
– any of the **internally rigid crustal blocks** of the lithosphere which moves horizontally
Tectonic plate
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– the process of which **one crustal blocks descends beneath another** such as the descent of Pacific Plate beneath the Andean Plate along Andean Trench
Subduction
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“ **Primary Structures: ** structures that are produced during formation of rock body.” (4)
* Depositional contact
* Unconformable contact
* Cross bedding
* Vesicles in basalt
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**“Secondary Structures**: structures produced after the rock body that they affect. (4)
– Fault contacts
– Folds
– Joints and shear fractures
– Tectonite fabric (cleavage, foliation and/or lineation)
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* Are produced when **rocks break or bend due to applied stresses within the earth.**
* Are **dynamically-produced patterns or arrangements** of rock or sediment that result from, and give information about, forces within the Earth.
*
Geologic Structure
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**Types of Geologic Structure** (3)
1. **Folds**
2. **Faults**
3. **Joints**
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– permanent **wavelike deformations** in layered rock or sediments
Folds
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– ** a fracture in bedrock** along which rocks on one side have **moved relative** to other side
Faults
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– a fracture on a rock **without noticeable movement/displacement**
Joints
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**Importance of the Study of Geologic Structure**
* In **engineering geology** , structural geology which is concerned with the **physical and mechanical properties of natural rocks. **
* Structural fabrics and defects such as faults, folds, joints, etc. are internal weaknesses of rocks which may affect ________________
stability of human engineered structure like dams, road cuts,
45
**Importance of the Study of Geologic Structure**
To the **environmental geologist**, hydrogeologist and hydrologist, structure sites of groundwater flow and penetration which may affect for instance,
seepage of toxic substances from waste dumps or seepage of salty water into quifers.
46
* Formed when beds or fabric are **deformed into curved or bent geometries on virtually any scale.**
* they are **wavelike bends in layered rock** . It represents rock strained in a **ductile** manner, usually under **compression** . this process results in **shortening and thickening of crust.**
Folds
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Parts of a Fold (5)
1. Axial Plane
2. Hinge Line or Axis
3. Limbs or Flanks
4. Trough
5. Crest
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(part of the fold)
that **divides it into its two limbs. **
Axial Plane
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(part of the fold)
* This Is the line formed by the **intersection of the axial plane with folded surface.**
* This is where folds curve.
Hinge Line or Axis
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(part of the fold)
The **sides of a fold or the outer parts of the fold** as it moves away from the axis of the fold
Limbs or Flanks
51
(part of the fold)
Is the line occupying the **lowest part of the fold**, or more precisely the line connecting the **lowest part of the same bed**
Trough
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(part of the fold)
Is the line occupying the **highest part of the fold,** or more precisely the line connecting the **highest part of the same bed**
Crest
53
Type of Folds (3)
Anticline, syncline, monoline
54
**Upfolded forms**, results in older rocks becoming enclosed within younger strata
| Type of Fold
Anticline
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**downfolded forms**, results in younger rocks becoming enclosed within older strata.
| Type of Fold
Syncline
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Is a **bend in the strata** resulting in a local steepening in the dip of the strata which is **almost flat lying on both sides away from the bend** – there is only one direction of dip
| Type of fold
monocline
56
Specific Type of Anticlines and Synclines (6)
1. Open/ Symmetrical
2. Isoclinal
3. Overturned
4. Asymmetrical
5. Recumbent
6. Plunging
57
both limbs of the fold dipping at **same angle away from fold axis**
| Specific type of anticline and syncline
OPEN/SYMMETRICAL
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both limbs of any fold are **parallel to each other, regardless of the dip of the axial plane**
| specific type of anticline and syncline
ISOCLINAL
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one limb of fold has been **tilted beyond vertical; axial plane is tilted**
| specific type of anticline and syncline
OVERTURNED
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**One limb** of the fold **dips more steeply** than the other
| specific type of anticline and syncline
Asymmetrical
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**limbs dip in same directio**n; the axial plane is essentially **horizontal**
| specific type of anticline and syncline
RECUMBENT
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The tilting of the fold **towards the front or back end**
| specific type of anticline and syncline
PLUNGING
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* An **up-arched** series of strata with beds on all sides **dipping away from the center** throughout 360 degrees -- rocks become progressively **younger away from the center of the structure**
DOMES
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A **down-arched** series of strata with beds on **all sides dipping towards the center** throughout 360 degrees -- rocks become progressively **older away from the center of the structure**
BASIN
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* Fracture along which **no appreciable movements** has taken place
* Accommodate stress during tensional and shear stresses associated with crustal movements.
* often occur in **very low-stress regimes, with broad, gentle warping of earth’s crust.**
* **don’t show evidence of slippage** whereas faults do.
* are arguably the **most common geologic structure** and can form in a variety of ways.
Fracture: Joint
66
Causes of Joints (6)
1. **Unloading or sheeting effects**
2. Stresses in **cooling magma**
3. **Tectonic stresses** causing fracturing essentially contemporaneously with the tectonic activity
4. **Residual stress** due to events that happened long **before fracturing**
5. Contraction due to **shrinkage** because of **cooling or desictcation**
6. **Surficial movemens** such as downhill movements of rocks or mountain glaciers
67
Classification of Joints
1. Geometrical
2. Genetic
68
Geochemical Classification
1. Strike Joints
2. Diagonal Joints
3. Bedding Joints
69
– are those that **strike parallel to the strike of the bedding of a sedimentary rock**
| Geochemical Classification
1. Strike Joints
70
– are those striking in a direction that lies **between the strike and direction of the dip** of the associated rocks
| Geochemical Classification
Diagonal Joints
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– are **parallel** to the bedding of the associated rocks
| Geochemical Classification
Bedding Joints
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Genetic Classification
* Shear Fracture
* Tension Fracture
73
– they are **parallel to the axial planes of folds **and **forms t right angle** to the axis of compression when load is released
| genetic classification
Release Joints
74
– they are **perpendicular to the axes of folds** resulting from slight elongation parallel to the axes of the folds
| genetic classification
Extension Joints
75
* Is a structure with ** major displacement of rock material along a crack in a rock**
* Are **brittle fractures** along which sliding has taken place
* Are ruptures along which the **opposite walls** have past each other. The essential feature is the **“Differential Movement”** parallel to the surface of the structure
Fracture: Faults
76
Parts of a Fault (7)
1. Hanging wall
2. Footwall
3. Fault-plane
4. Fault line, fault
5. strike of the fault
6. dip of the fault
7. hade
77
**Classification of Fault:**
Faults like joints may be classified on the **basis of their geometry or their genesis**. The bases of five different geometrical classifications are:
1. **Rake of the net slip**
2. **Attitude** of fault relative to the attitude of the adjacent rocks
3. The **pattern** of faults
4. The **angle** at which the fault slip
5. The **apparent movement** of fault
78
– is the **total displacement**; it is the distance measured on the fault surface between two formerly adjacent points situated on opposite walls of the fault
Net Slip
79
Geometric Classification (3)
1. Strike-slip fault
2. dip-slip fault
3. oblique fault
80
* Is one in which the **net slip is parallel to the strike of the fault. **
* In this fault, movement is primarily **horizontal**.
| geometric classification
Strike-slip Fault
81
* Is one in which the **net slip up or down the dip of the fault.**
* in this faults, **movement is parallel to the dip** of the fault plane and typically shows a **strong component of vertical motion.**
| geometric classification
2. Dip-slip Fault
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* A fault which has a **major dip slip and strike slip component**
| geometric classification
3. Oblique Fault
83
Genetic Classification: Dip-slip
Normal fault and reverse fault
84
Genetic Classification: strike-slip fault
left-lateral and right lateral
85
faults in which crustal block above the fault plane **(hanging wall) moves up relative to crustal block below the fault plane (foot wall).**
-this faults develop in response to **compressional stress.**
Reverse Faults
86
faults in which crustal block above the fault plane **(hanging wall) move down relative to crustal block below the fault plane (foot wall).**
-this faults develop in response to **tensile stress.**
Normal Faults
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* this fault with **very low angle, or very gently inclined (<45 deg) ** fault plane. Associated with strong, horizontally oriented, compressional stresses.
Reverse Faults: Thrust Fault
88
are **low-angle faults** which the **net slip is large, generally in miles**
Overthrust fault
89
* movement along fault is **horizontal along the fault** (similar to notion of transform faults in plate tectonics), i.e. offset is parallel to the trend or strike of the fault plane.
* Forms during **shearing stress**
* are **vertical with no hanging wall or footwall**
* **Neither** shortening or extension occurs
* offset surface features such as **streams and valleys**
Strike-slip faults-
90
is the block **above** the fault
| Parts of a Fault
Hanging Wall
91
is the block below the fault
| Parts of a Fault
Footwall
92
is a **planar** fault surface
| Parts of a Fault
Fault Plane
93
is the **intersection** of the fault with the surface of the earth
| Parts of a Fault
Fault-line, Fault Trace or Fault Outcrop
94
is the **trend of a horizontal line** in the plane of the fault
| Parts of a Fault
Strike of the fault
95
is the **angle** between the **horizontal surface and the plane** of the fault
| Parts of a Fault
Dip of the fault
96
is a an **angle equals 90 deg**. Less than the angle of dip. It is also defines as the **angle between the fault plane and a vertical plane** that strikes parallel to the fault.
| Parts of a Fault
Hade
97
Effects of geologic structures in engineering structures
1. Effects of Folding
2. Effects of Faulting
3. Effects of Jointing
4. Effects of Unconformities
98
Effects of Folding
* Change in attitude
* Shattering of rocks (weak in strength parameters, porous and pervious and nature)
* Strained nature
99
* Folded rocks are greatly strained. Their removal for tunneling can cause rock explosions.
* Along crests of folds, the rocks are in tension, therefore highly unstable.
* Along the troughs, rocks are highly compressed, hence tough, and offer greater resistance to excavation for tunneling
* Tunneling can be done along the limbs
(Effects of folding)
Location of tunnels:
100
* Better rock quality available
* Fractures associated with crests and troughs are absent along the limbs
* Seepage problems along the crests and troughs can be avoided
(Effects of folding)
Quarrying should be done along the limbs:
101
* Folds often furnish excellent conditions to trap groundwater
* Fractures present in folded strata act as channels for groundwater movement
(Effects of folding)
Groundwater occurrence:
102
* Ground stability depends on the mutual relation of the dip of the beds and the slope of the cutting.
* If the surface slope and the dip are in opposite directions, the ground is stable
* If the surface slope and dip collide, the ground is unstable.
(Effects of folding)
Haul roads along hill slopes
103
* Suitable cap rocks are also an essential requirement
* Crests of folds offer convenient places for the occurrence of ore deposits
(Effects of folding)
Oil and gas deposits are often associated with anticlines
104
* Fracture and shattering of rocks along fault zones
* Serves as pathways for water, causes leakage
* Fault zones lubricated with water are potential sites for further movements
* Faults bring together different rocks, hence homogeneity is lost
* Fault zones are highly undesirable for construction of roads, due to the possibility of landslides.
* However, fault zones are often rich in minerals, and favor different processes that eventually lead to mineral formation.
Effects of Faulting
105
* Sources of weakness in rocks, pathways for seepage of water
* Jointed rocks, lubricated by the presence of water, are susceptible to motion
* Joints are usually treated by grouting
* Only a well-jointed and porous rock can become a good aquifer or an oil and gas reservoir
* Joints and landslides:
*
Effects of Jointing
106
* Allow for the percolation of water
* Unconformity indicates a break in the sequence of rocks, and hence, their engineering properties
* Exhaustive studies have to be done to analyze the mechanical properties of rocks in the vicinity of an unconformity.
*
Effects of Unconformities
