Structural Geology: Deformation and Mountain Building

1. Structural Geology: Deformation and Mountain Building

2. Inner core: Solid iron Outer core: Liquid iron, convecting(magnetic field) Mantle (Asthenosphere): Solid iron-magnesium silicate, plastic, convecting Crust (Lithosphere):Rigid, thin 5-30km Tectonic Stresses Large Scale Strain of the Crust - Geologic Structures Crust: Rigid, Thin Mantle: Plastic, Convecting

3. Tectonic Stresses resulting from Internal Energy (heat driving convection) Strains (deforms) the Mantle and Crust Bends Rocks ductile strain (Folds) Breaks Rock brittle strain (Joints) Moves large blocks Faults Releases energyEarthquakes Tectonics and Structural Geology

5. Folds and Faults (Palmdale, Ca)

6. Kaynasli, Turkey

7. Divergent (Tensional) | Convergent (Compressional) | Transform (Shear) e.g., Pacific NW Stresses at Plate Boundaries

8. Geological Structures • Different stresses result in various forms of strain (geologic structures) • Folds (compressive stresses may cause ductile strain) • Faults (Any type of stress may cause brittle strain. The type of fault depends on the type of stress)

9. Geological Structures • Fault: a discontinuity surface across which there has been shear displacement • Hangingwall: the wall and body of rock above an inclined fault • Footwall: the wall and body of rock beneath an inclined fault

10. Geological Structures • Normal Fault: hanging wall moved downwards compared to the footwall • Reverse Fault: hanging wall moved upwards compared to the footwall • Thrust fault: low angle reverse fault

11. Geological Structures • Strike Slip Fault: displacement parallel to the fault plane. • Can be left or right handed!

12. Stikes and Dips are used to identify geologic structures

13. Strike and Dip • Define and map the orientation of planar features • Bedding planes (sedimentary rocks) • Foliation • Joints • Faults • Dikes • Sills • Ore Veins Fig. 10-4, p. 221

14. Strike and Dip Strike and Dip Map Symbol • Strike: The line of intersection between the plane and a horizontal surface • Dip: Angle that the plane makes with that horizontal plane Fig. 10-4, p. 221

15. Anticline (fold)

16. Syncline (fold)

18. Plunging Anticline

19. Fold Terminology • Hinge: the greatest curvature of a folded surface • Axial plane: a planar surface defined by the successive positions of fold hinges • Plunge Axis Axis

20. Plunging Anticline, Colorado

21. Domes and Basins

23. Brittle Strain  Joints • When shallow crust is strained rocks tend to exhibit brittle strain

24. Sheet Joints

25. Defining Fault Orientation • Strike of fault plane parallels the • fault trace • fault scarp • Direction of Dip of the fault plane indicates the Hanging wall block

26. Fault: • Movement occurring along a discontinuity • Brittle strain and subsequent movement as a result of stress • Fault terminology

27. Fault: When movement occurs along a discontinuity Fault type depends on the type of stress Faults

28. Normal Faults

29. Normal Faults, Horsts and Grabens

30. Horsts and Grabens • Older Rocks are exposed along the ridges formed by the horsts • Younger rocks lie beneath the grabens • Sediment fills in the linear valleys Horst Horst Graben Graben

31. Nevada • “Washboard topography” is the result of Horsts and Grabens • A.k.a, Basin and Range • E.g., Humbolt Range • E.g., Death Valley (Graben)

32. Horst and Graben, Nevada Horst Graben Humboldt Range, Northern Nevada

33. Horst and Graben, Nevada Horst Graben Humboldt Range, Northern Nevada

34. Reverse and Thrust Faults • Compressive stress causes the hanging wall to move upward relative to the foot wall  Reverse Fault • At convergent plate boundaries ancient rocks can be thrust over younger rocks  Thrust Fault

35. Thrust Fault: Glacier NP, Montana Old Younger

36. Strike Slip Faults • Physiographic Features