Structural Geology Flashcards
What provides the energy for rock deformation?
The earth’s energy which is converted to mechanical energy
Define lithosphere.
The solid outer part of the earth, including the upper mantle and crust
What do tectonic forces do to rocks in the lithosphere/
Squeeze, stretch, bend, and break them
Define stress.
Applied force and pressure
What is the difference between uniform and differential stress?
Uniform stress is a condition in which the stress is equal in every direction.
Differential stress is stress not equal in every direction – leading to deformation.
Define strain.
The change in length, shape, or volume of a rock.
Strain describes the deformation of a rock
What are the 3 stages of deformation a rock undergoes when stress is applied? (in order)
Elastic deformation -> ductile deformation -> fracture
Describe elastic deformation of a rock.
A state in which all strain is reversible when/if stress is released.
Describe ductile deformation.
Strain is irreversible, the rock will remain deformed after stress is released
Describe fracture of a rock.
When stress exceeds the limit of elastic and ductile deformation a rock breaks
What is ductile deformation also known as?
Plastic deformation
What conditions are more likely to produce ductile deformation?
High temperatures, low strain rates, high confining pressures.
What conditions are more likely to cause brittle deformation?
Low temperatures, high strain rates, low pressures
What causes fracture on a microscopic level?
If the stress exceeds the strength of the bond between atoms, either the atoms move to another place in the crystal lattice to relieve stress OR the bonds break and fracture occurs.
What are tilted rocks evidence of? Why?
Deformation, because rocks are laid down horizontally
What is a fault?
A fracture along which visible displacement has occurred.
What is a joint?
A fracture along which no observable movement has occurred
What is the difference between a fault and a joint?
Fault - observable movement on fracture
Joint - No observable movement
What features are faults classified based on?
Dip of the fault, relative movement either side (hanging wall vs foot wall)
Describe a normal fault.
Tensional stress pulls the two sides of the fault apart.
It will have a hanging wall on one side and a footwall on the other
What is difference between a hanging wall and a footwall on a normal fault?
The footwall will be vertically higher at the fault with the hanging wall dipped lower
Is a normal fault the result of ‘pushing’ or ‘pulling’?
The two sides are ‘pulled’ away from eachother’
Describe a reverse fault.
The two sides of the fault are subject to compressional stress
What is the difference between a hanging wall and a footwall for a reverse fault/
Footwall is lower, hanging is higher
What is the simple difference between a normal fault and a reverse fault?
Normal = tensional stress
Reverse = Compressional stress
- Hanging and footwalls opposite ways round.
Describe a strike-slip fault. When are these hard to identify?
Horizontal movement.
- Hard to see in cross sections
What is an oblique slip fault?
A combination of vertical and horizontal movements
Describe a thrust fault. Where are these common?
A very low angle reverse fault, less than 15°
- Common in mountain chains
What is a fold an example of?
A ductile deformation
What does dip of a fold measure?
The angle in degrees between a horizontal plane and the inclined one
What is the strike of a fold?
The compass direction of the horizontal line formed by where the inclined plane enters/meets the horizontal one
What is the difference between anticlines and synclines?
Anticlines have the older rocks at the core, whereas synclines have the younger rocks at the core
What makes an anticline/syncline isoclinal?
Parallel limbs
What makes an anticline/syncline open?
Its symmetrical and both limbs dip equally from the vertical
What makes an anticline/syncline overturned?
When both limbs tilt in the same direction but one has a steeper angle
What makes an anticline/syncline recumbent?
When the limbs are near horizontal
