Lecture 9 Flashcards
What does structural geology study?
Shape and forces responsible for deformation of Earth’s crust.
What is deformation in geology?
A general term for changes in the original form, size, location, or orientation of a rock body.
Where does most crustal deformation occur?
Along or near plate margins.
What are the three main types of stress affecting rocks? (CTS)
- Compressional stress: Shortens a rock body.
- Tensional stress: Elongates a rock body.
- Shear stress: Causes slippage, like playing cards sliding past each other.
What are the two stages of rock deformation?
- Elastic : Recoverable changes.
- Plastic : Exceeds limit: folding, flowing, or fracturing.
How does temperature affect rock deformation? (IMPORTANT)
- Brittle deformation: Low temp/pressure near surface.
- Ductile deformation: High temp/pressure, allowing rocks to flow.
What is strike in geology?
Compass direction of line produced by intersection of inclined rock layer or fault with horizontal plane.
What is dip in geology?
The angle of inclination of a rock unit or fault measured from a horizontal plane, at 90˚ to the strike.
What are folds in sedimentary strata?
Wave-like undulations formed by compressional stresses that shorten and thicken the crust.
What are the parts of a fold?
- Limbs (Two sides)
- Axis (Line down the crest)
- Axial plane (Divides symmetrically)
- Plunge (Axis inclined at angle)
How does rock type affect rock deformation? (IMPORTANT)
Mineral composition and textures of rock influence deformation style
How does time affect rock deformation? (IMPORTANT)
Small amounts of stress over geologic time cause large changes
What are the types of folds?
- Anticline: Upward-arched layers.
- Syncline: Downward-troughed layers.
- Monocline: Step-like folds.
- Domes: Up-warped, with oldest rocks in the center.
- Basins: Down-warped, with youngest rocks in the center.
What are joints in rocks? (IMPORTANT)
Fractures with no displacement, often occurring in parallel groups.
What are the significance of joints? (IMPORTANT)
Concentrate chemical weathering.
Important for mineral deposits.
Represent construction risks.
What causes of joints types ? (IMPORTANT)
- Columnar joints (igneous)
- Gently curved due to sheeting
- Brittle fracture due to crustal deformation
What are faults?
Fractures in rocks with appreciable displacement, causing earthquakes.
What are dip-slip faults?
Faults with movement parallel to the dip of the fault surface. Examples:
- Normal faults: Hanging wall moves down.
- Reverse/thrust faults: Hanging wall moves up.
What are strike-slip faults?
Horizontal displacement parallel to the strike. Types:
- Right-lateral: Opposite block moves right.
- Left-lateral: Opposite block moves left.
Fault scarps ?
Long low cliffs produced by up and down displacement
Hanging wall ?
Rock above the fault surface
Footwall ?
Rock below the fault surface
Graben ?
Central block bounded by normal faults ; drops as plates separate
Horst ?
Raised blocks between grabensm, also bounded by normal faults.
