1. Ch 15 (Part I): Crustal deformation
Today:
Ch 15 (Part I): Crustal deformation

3. Ch15 (Pt I): Crustal Deformation
2) Mapping geologic structures
3) Folds

4. Chapter 15: Crustal deformation
Examines forces that deform rock & resulting structures
Why do we care?
geological past
oil & natural gas
metal ores
building locations (hazards)

5. Chapter 15: Crustal deformation
Basic geologic structures associated w/ deformation:
1) Folds
2) Faults
3) Joints
4) Rock cleavage
5) Foliation
Chapter 7
Metamorphic Rocks
Been there, done that

6. deformation of rock from the applied stress
Strain
force applied to a rock
deformation of rock from the applied stress

7. 1) Deformation: Stress
Confining pressure: force equal in all directions
Differential stress: force not equal in all directions

8. Confining pressure: force equal in all directions
1) Deformation: Stress
Confining pressure: force equal in all directions
Differential stress: force not equal in all directions
Brittle deformation
rocks crack/fracture
Ductile deformation
rocks flow
Shallow in crust
Deeper down

9. Compressional stresses:
1) Deformation: Stress
Confining pressure: force equal in all directions
Differential stress: force not equal in all directions
Compressional stresses:
shortening

10. Compressional stresses:
1) Deformation: Stress
Confining pressure: force equal in all directions
Differential stress: force not equal in all directions
Compressional stresses:
shortening
Tensional stresses:
elongation
T&L Figure 15.4

11. Compressional stresses:
1) Deformation: Stress
Confining pressure: force equal in all directions
Differential stress: force not equal in all directions
Compressional stresses:
shortening
Tensional stresses:
elongation
Shear stresses:
bending (shearing)
T&L Figure 15.4

12. 2) Mapping geologic structures
Deformational processes create faults folds, joints
rock structures
Visible when rock beds are exposed at surface
out crops

13. 2) Mapping geologic structures
Strike and dip
Strike
Dip
trend relative to north,
measured as an angle
angle of tilt of a bed

17. 3) Folds
series of wavelike bending of once-flat rock layers
many sizes: microscopic to 100’s of meters
compressive stresses: shorten+thicken crust

18. 3) Folds
series of wavelike bending of once-flat rock layers
many sizes: microscopic to 100’s of meters
compressive stresses: shorten+thicken crust

19. 3) Folds Types of folds Other deformations
anticline - arching hill of layers
syncline trough of layers
monocline - one-limbed fold
dome - circular upwarping
basin - circular downwarping
hogbacks - erosion-resistance strata

26. hogbacks
Strata resistant
to erosion