1. Brittle Deformation (3) Kinematic indicators (1) & normal faults
GLY 326 Structural Geology
Brittle Deformation (3)
Kinematic indicators (1)
&
normal faults
Autumn, of the year that we are in

2. Strike-Slip fault Normal fault Reverse fault
Remember the types of faults???
Strike-Slip fault
Normal fault
Reverse fault

3. Slickensides and Slickenlines
Slickensides: Polished surfaces (neo-minerals coating)
Slickenlines : striations or grooves
18th century slang for “slick side”

5. They often tell the movement of the fault…

6. (asperites)

7. Asperites

11. Normal Faults Caused by tension (pulling apart)
Hanging wall moves down relative to footwall
Horst and Graben topography (i.e. Basin and Range)

14. To draw a normal fault in a map we take the strike of the fault plane (which is roughly the same as the trace)
older
younger
And mark the hanging wall with “teeth”…

15. The real situation:

17. Again 18th century slang:
Graben is german for “ditch” and Horst german for “heap”

18. Horst and Graben Formation
Where?….

19. Mid-Oceanic ridges

20. Examples of active continental Rifts:
Rift margins usually remain elevated, even after oceanic crust begins to develop. Darker browns represent higher elevations in satellite image of Red Sea.

21. Local example of inactive continental Rifts: (aulacogen)

22. Examples of Aulacogens (Unsuccessful Rifts or Failed Rifts)
All are Precambrian except the Oklahoma & Reelfoot Aulacogens which are Early Paleozoic.

23. Metamorphic core complexes
They occur throughout Western North America
Associated with Recent extension

24. Horst and Graben Formation

25. Graben in Iceland

26. Rift Structure
Most of the rift models illustrating rifts show a symmetrical rift with horsts and graben. Lithospheric crust is stretch symmetrically and hot asthenosphere domes up feeding the igneous activity.
This has been called the “pure shear” Model
This model implies planar faults, and fault blocks that do not rotate, just slide down the planar faults.

27. landslides

28. Rift Structure
However most rifts have rotated fault blocks which can only be produced by listric normal faults.

29. Rift Structure
This suggests that many rifts are asymmetric and underlain by large a listric detachment, with smaller listric faults merging into it.

30. Rift Structure
Two examples illustrate these different models of Rifting: The Viking Graben, and the Suez Graben.

31. Rift Structure
Two examples illustrate these different models of Rifting: The Viking Graben, and the Suez Graben.

32. Formation of Rift Systems
All rift systems (as well as any large fault) consists of smaller segments. Faulting is initiated at many points along the potential rift zone, and these small faults grow and eventually join up with others to form the large regional rift system.

33. Formation of Rift Systems
Mismatch : accommodation or transfer zone.
(in plate tectonics: transform fault).

34. Formation of Rift Systems
Accommodation can occur if fault segments have opposing dips!

35. Formation of Rift Systems
Transfer or accommodation zones with significant strike-slip component: transform fault.