Reading

1. Reading • Displacement chapter, in library (not available online). Read 18.0-18.4 plus 18.12. Concept map due Wednesday. • Davis and Reynolds “ Structural Geology of Rocks and Regions” p. 319-370, also on reserve in library • Concept maps not required for D&R chapter

2. Why Study Reverse Faults? • Host the largest, and potentially most destructive earthquakes (subduction zone thrusts). Low dip requires that faults have large surface area in brittle "seismogenic zone" and that this surface area is close to ground surface where we live. • Associated with mountain building and collisional tectonics. Low-angle faults with big displacements have been known since 1800's (Lapworth). • Influence positions of ore deposits (high-angle reverse faults) and hydrocarbons (thrusts).

3. Shaw and Shearer: Blind thrust fault beneath Los Angeles metropolitan area, interpreted from seismic reflection profiles and precise earthquake locations

4. Pittman and Ryan

5. Initiating subduction • Generally will reactivate pre-existing structures, such as rift-related features preserved on passive margins (producing continental arc) or transform faults in mid-ocean ridges (producing island arc)

6. Structural components of convergent margins

7. Other elements of thrust belts • Thrusting may be thin-skinned (involving only sedimentary cover) or thick-skinned (involving basement) • Large overturned folds, or nappes (French word for napkin) may form

8. Accretionary tectonics • First recognized in North American Cordillera • Far-traveled terranes may have docked to continent along either reverse or strike-slip faults

9. X-section through Cordilleran Terranes • Sutures bound accreted terranes • Exotic terranes include arcs, microcontinents, and slivers of colliding continental material

10. Much of what we know about thrust terranes is a gift of erosion • Klippe (pl. klippen), from German word meaning ‘slice’, is the erosional remnant of a hanging wall • Window is an erosional hole through hanging wall, allowing footwall to be viewed • Autochthonous material is in place • Allocthonous material has been transported along faults from location of origin

11. Elements of a fold and thrust belt. Note the asymmetry of both horse geometry and folds that records transport direction (also known as vergence)

12. Break-thrust fold

13. Development and 3D form of a fault-bend fold

14. Fault propagation fold

15. Trishear zones exhibit tighter folds with increased proximity to fault tip (blind thrust)

16. Patterns of detachment folds are less regular than other fault-related folds

17. Extension may also occur locally in association with subduction zones

18. …Or in association with continent-continent collisions, where ‘orogenic collapse’ is one way that mountain systems achieve isostatic equilibrium

19. Mechanical paradox • Thrust movement on low-angle surface with ‘typical’ coefficient of friction of rock requires stresses high enough to break the rock • To understand how this motion takes place, we need to think about concepts of displacement, stress, and fault mechanics

20. Three descriptions of mechanical interactions • Displacement describes the movement of particles with respect to an external reference frame • Deformation can be described by a displacement field • Translation • Rotation • Shape change (distortion) = strain • Stress is force per unit area

21. Components of Deformation

22. Deformation

23. Three categories of displacement • Relative particle motion can be described even if part of the system is fixed in space