1. Announcements: Final Exam Monday, Dec. 16, 11-1 this room

2. Recap of Monday's whirlwind tour: 1) Archean to Middle Proterozoic growth and deformation of the N.A. craton 2) Late Proterozoic – Cambrian rifting of the W. NA margin 3) Paleozoic passive margin sedimentation 4) ~350 Ma Antler orogen to west 5) 300-250 Ma Ancestral Rockies to east 6) Permo-Triassic Sonoma orogeny to west

3. Bigger picture: formation of the Cordilleras due to long- lived oceanic subduction

4. The Sevier orogeny: E-directed thrusting behind a magmatic arc– "retro-arc" fold-thrust belt and associated foreland basin system

5. What's going on at this time (~60 myr ago?) Eastward sweep in magmatism Basement-involved deformation "Laramide" orogeny

6. Magmatism starts sweeping back to west – 45 Myr ago More "Laramide" deformation

7. More westward sweep in magmatism- Major change in style of deformation!

8. Rifting and development of Cordilleran metamorphic core complexes related to major crustal extension

9. Basin and Range Extension Eruption of Columbia River basalts Magmatism back to west

10. Growth of Basin and Range Province

11. Today!

12. Relating plate tectonics to continental deformation

13. Concept of "Suspect" terranes- possibly far- traveled and torn off of other continents, rafted across large tracts of oceans and finally accreted to W. N.A. Crustal "immigration"

14. Review for: Final Exam Monday, Dec. 16, 11-1 this room Format: Short essay questions (~1 paragraph), SKETCHES!, some short answer questions

15.  c = critical shear stress required for failure  0 = cohesive strength tan  = coefficient of internal friction  N = normal stress Recall Coulomb's Law of Failure In compression, what is the observed angle between the fracture surface and  1 (  )? ~30 degrees!

16. Anderson's theory of faulting

17. Summary Thrust systems: 1. Accommodate significant crustal shortening 2. Basal detachment; decoupling within the crust 3. Faults have ramp and flat geometries 4. Fault place older/higher grade rocks over younger/lower grade rocks 5. Faults cut up-section 6. Faults generally propagate (get younger) toward the foreland 7. Younger and structurally deeper faults rotate older faults to steeper angles

18. Colorado Plateau monoclines may be related to thick-skinned deformation- basement- involved thrusting

19. Fault-bend folds

20. Fault-propagation folds

21. monoclines as "drape" folds

22. Mechanical "paradox" of large thrust sheets

23. Possible explanation- water pressure plays a big role  c = tan  (*  N ), where tan  is the coefficient of sliding friction and *  N =  N – fluid pressure

24. Critical Taper Thrusts belts are wedge shaped- characterized by a topographic slope (  ) and a decollement dip (  ) Only at some critical angle (  +  ), will the thrust belt propagate

25. Sequence of events:

27. summary of strike-slip-related deformation

28. Tectonic significance of strike-slip faults (1) oceanic transform faults (2) trench-trench transform faults (Alpine fault) (3) trench-ridge transform fault (San Andreas) (4) Oblique convergence (Denali fault) (5) transfer fault between thrust systems (Altyn Tagh?) (6) continental extrusion (Altyn Tagh?)

29. Cleavage: closely spaced, aligned, planar surfaces; associated with folds- impart a splitting property to the rock- often cuts bedding

30. continuous cleavage under a microscope, showing domainal nature

31. Origin of cleavage + passive folds Pressure solution (dominant!!)

32. In brittle regime: joints, tensile fractures, shear fractures (faults!), pressure solution (cleavage development)- deformation mechanisms depend on pressure! What about deformation in the deeper crust?

33. Flattening of strong layers surrounded by weak layers may cause strong layers to "neck" and form boudins.

34. Mylonitic foliation: Forms due to grain-size reduction by a mix of brittle and plastic deformation in shear zones brittle deformation of feldspar porphyroclasts plastic deformation of quartz "ribbons" and mica

35. Stretching lineation

36. Deformation mechanisms: Processes that permit rocks to deform at the microscopic and atomic scale

37. How much and when were rocks buried to depth? When were rocks deformed? When were rocks metamorphosed? When were rocks brought up from depth (exhumed)? How fast? How did this all happen? To get at displacement on BIG structures- need to know depths/temperatures from which rocks were brought up- thermobarometry To get at timing- need geochronology and thermochronology

38. Thermobarometry: Quantitative determination of temperature (T) and pressure (P) using equilibrium reactions

39. THERMOCHRONOLOGY: determining the time when a rock was at a certain temperature

40. (1) aseismic movements that occur in between earthquakes

41. Real-time action; Real-time measurement- what can we learn from seismology about structural geology?? 1) Location and depth of faulting (brittle-ductile transition) 2) fault plane solutions- orientation of fault and sense of slip- geometry and kinematics 3) Energy release- size of fault, rupture characteristics- unidirectional, bidirectional, chaotic?

42. What we are learning from GPS 1) Plate tectonic assumptions OK- but only to first order- Within plate deformation can be huge 2) How continents deform during orogenesis- diffuse? plate like? 3) What parts of faults are slipping vs. what parts are "locked" up- important for EQ predictions 4) unprecedented knowledge of recent movements on Earth

43. Landers Earthquake What can we learn from InSAR?

44. Study the earthquake cycle- recurrence intervals of major events through neotectonic studies 1) study deformed historic sites of known ages (Great Wall of China) 2) Paleoseismology 3) offset geomorphologic surfaces + surface dating

45. Continental deformation- what we are learning from Tibet

46. Active deformation in Tibet- normal and strike-slip faulting- WHY?